Contents:
Notes on the Troubleshooting and Repair of Small Gasoline Engines and Rotary Lawn Mowers
Copyright (c) 1994, 1995, 1996, 1997, 1998
All Rights Reserved
Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied:
Can you see above the weeds? --------------------------- Most problems with gasoline powered rotary lawn mowers as well as other small engines have simple and inexpensive solutions. For example: * A mower that is hard to start, runs roughly, or dies at the first opportunity may just need a new spark plug or to have its carburetor cleaned. * A mower that won't start after its blade hits an obstruction may just need one or two 25 cent locking keys replaced. This document addresses some of the most common ailments and provides detailed instructions for their diagnosis and cure. In addition, it provides detailed maintenance guidelines to prolong the life and happiness of your lawn mower(s) and other yard equipment. For electric lawn mower and other electric yard tool problems, refer to the document: "Notes on the Troubleshooting and Repair of Small Household Appliances and Power Tools" which includes chapters on basic electrical theory (relax, no rocket science) and electric motor testing and repair information. We will deal with problems the weekend gardener is likely to run into (sometimes, literally!) as well as semi-detailed overhaul instructions. One or more of the books listed in the section: "References" can be used to supplement this document and can provide much more detailed troubleshooting and repair procedures. Even if you don't know the difference between a carburetor and a crankshaft, you may still be able to do some of your own work. (Hint: if you drop one of these on your foot, the crankshaft will hurt a lot more!) We begin with an introduction to small engine technology and have more-or-less separate chapters on basic maintenance, intermediate troubleshooting and repairs, and more extensive overhaul procedures. Note: this "Lawn Mower FAQ" is in the early stages of construction. I welcome comments, additions, hints, corrections, funny or other stories, etc. As the title implies, it is oriented toward the gasoline engine powered rotary lawn mower. However, much of the general information applies to a wide range of yard and shop equipment powered by small 2 and 4 stroke gasoline engines.
Despite all the dire warnings (don't forget that the lawyers need to make a living!) it is possible to use, store, maintain, and repair gasoline powered equipment safely. Mostly, the necessary precautions are just common sense - for example, don't smoke around gasoline (well, don't smoke at all but that is not a part of the charter of this document!). The following represent the basic precautions to take when performing maintenance or service procedures on gasoline powered equipment and dealing with gasoline in general: * NEVER work on a gasoline powered engine indoors unless it has been totally drained of gas and given time for the residue to evaporate. Gasoline, in particular, is extremely explosive. It is not the liquid but the vapors - at a wide range of concentrations. The various solvents used for cleaning carburetors and degreasing engine parts are also very flammable. The vapors are also not exactly beneficial to good health. * ALWAYS store gasoline in an approved gasoline can. These will be red in color. They are not the same as (blue) kerosene cans! The round metal or thick plastic type sturdier than the rectangular thin (sheet metal) cans which may collapse in cold weather. NEVER NEVER store gasoline in glass or plastic bottles. NEVER store gasoline indoors or anywhere else that any vapors can build up or in a location near an open flame (gas or oil heater, etc.). * ALWAYS stop the engine before refilling the fuel tank. If possible, add gasoline when the engine is cold - a splash on the hot cylinder could catch fire. Rinse off spills with water or wait till they evaporate before starting the engine. * NEVER attempt to run a gasoline engine indoors. In addition to the general fire and explosion hazard, internal combustion engines produce significant amounts of carbon monoxide - a colorless, odorless, deadly gas. * NEVER ever smoke while working on gasoline powered equipment even if you are willing to kill yourself slowly by smoking. * DISPOSE of used engine oil in a safe manner - don't just dump it down the drain or in the trash. Your local service station or recycling center may accept engine oil or recommend a place for its environmentally friendly disposal. Used engine oil is also a carcinogen. Therefore, avoid excessive skin contact during servicing procedures. * AVOID going near the spark plug wire when the engine is running or even if you are just pulling on the starter cord. The high voltage is not really particularly dangerous since the available current is extremely small but it will not be pleasant and the reflex reaction may make you do something you will regret. * ALWAYS disconnect the spark plug wire and tie it safely away from the spark plug terminal (several inches minimum) when doing any work on the engine's moving parts. You don't want any chance of the engine starting on its own. An even better alternative is to remove the spark plug entirely. Even an engine that normally takes 10 pulls to start can do funny things that might lead to unpleasant accidents. Despite the fact that it will not start now no matter what you do, the underlying problem could actually be a flooded carburetor or something else which may correct itself while you are working. Never take chances. Note: Modern mowers have at least two systems for stopping blade rotation fairly quickly and keeping it stopped if the dead-man bar is released. These will be either an engine kill and blade brake (on most inexpensive mowers) or a blade brake/clutch which keeps the engine running but stops the blade (on high-end machines). * Under no circumstances should the dead-man bar be tied down unless the spark plug wire is removed and safely tied away from the spark plug terminal. Even removing the gas tank isn't necessarily enough to prevent accidental starting. Many types of carburetors contain a reservoir (float chamber) which may still hold sufficient gas for several minutes of operation. * Older mowers (or other yard equipment) may have no blade brake and only a momentary contact for stopping the engine by shorting the spark plug terminal to the frame. These mowers are on a hair trigger and just rotating the blade can start them up when you least expect it.
While you probably did not purchase your lawn mower specifically for the joys of repairing it, there is always a chance that despite all your precautions, the blade will strike a rock that just happened to grow out of the ground when you weren't looking. Therefore, it makes sense to be prepared. Basic servicing of small engines doesn't require a $500 tool caddy. However, some basic hand tools and other items will be needed. * A good quality set of socket wrenches is essential. For small engine work, a 3/8" ratchet and a set of sockets from 1/4" to 1" as well as a special spark plug socket (usually a deep 13/16" type - check for your particular engine(s)) will suffice. A basic set from Sears (Craftsman) should be fine and will come with a lifetime replacement warranty as well! If you have never invested in a socket set, now is the time. Forget about those $4 specials, however, as they are generally worse than useless. A word to the wise: you really must have a socket set to do any kind of work on small engines. Slip joint pliers or worse - ViseGrips - just will not do! While box-end (closed) wrenches may be used for certain bolts, some simply are not accessible without a properly sized socket (like cylinder head bolts). * A variety of good quality screwdrivers - both straight and philips. * Needlenose and utility pliers. * Wire cutters and strippers. * Ball-peen hammer or other metal hammer. * Rubber mallet. * Funnel, drain pan, plastic milk jug for used oil. These can be discards from the kitchen. * Old rags, cotton swabs, paper towels, etc. for cleaning. An old but soft paint brush for getting dust and dirt our of various places. * Wood blocks for propping things up or securing the blade or flywheel when loosening or tightening. Other drift (scraps) of wood and soft metal. * Torque wrench. An adequate model that will work with your 3/8" sockets can be purchased for around $10. Setting the torque - tightness - on certain engine bolts is critical to proper operation and long life. * Feeler gauge - a set of precise thickness strips or wires for setting spark plug and point gaps. A .020" and .030" should suffice for basic maintenance. * Flywheel puller - build or buy. See the section: "Flywheel removal" and inspection". If purchased, it must be one designed for your model engine, not just something you picked up in the hardware store marked 'flywheel puller'! Briggs and Stratton, Tecumseh, and others sell tools specifically for their engines. This is the easiest way to remove the flywheel. * Carburetor cleaner - this comes in a spray can. It is also probably as flammable as gasoline, toxic, and will eat plastics and painted surfaces. Therefore, use only in a well ventilated area or outdoors and take appropriate precautions. * A tube of thread-lock comes in handy as well as some anti-seize compound like graphite grease for the muffler/exhaust bolts and spark plug.
Many people who have never used a gasoline engine powered piece of yard equipment are intimidated by all the warnings with respect to the explosive nature of gasoline. They then opt for an electric lawn mower instead of gas. For many, this is the correct choice. There are a different set of precautions to follow but they are fewer and seemingly less of a threat. Electric equipment is in some ways more environmentally friendly generating no pollution (though the electricity had to generated somehow). Once the equipment is unplugged, there is nothing to worry about with no gasoline to store. Little maintenance is needed and there is never any issue of disposing of used engine oil - since there is no engine oil. Electric equipment is also usually - though not always - somewhat quieter. The main disadvantage of line powered electric equipment is that it is tethered to an electric outlet by the power cord. This can become quite a nuisance after a short while. Battery powered equipment has tended to less powerful and more finicky to deal with than similar equipment powered from a line cord. And, electric mowers tend to be less powerful than similar equipment using a small gasoline engine. Where your yard is relatively small (say, less than 50 feet to an electric outlet from the farthest point), a corded mower may be a good choice. It will be less expensive than typical battery powered mowers and most gasoline powered mowers, and vitually maintenance-free. Just make sure you use a proper outdoor heavy duty extension cord - probably one size LARGER (lower AWG wire size number) than what the manufacturer recommends. This will assure minimal loss of voltage due to its resistance - and every bit of power you have available will help! A somewhat lighter duty outdoor cord can be used for the first few feet if that makes maneuvering the mower easier. The main thing to watch out for is accidentally cutting the cord by running over it. Mowing in a back-and-forth pattern while moving away from the outlet helps. If you do cut the cord - don't panic. At most, you will need to shorten it a couple of feet and install a new socket on the end of what is left AFTER pulling the plug! If the outlet is now dead, at most you have tripped the circuit breaker or GFCI, or blown the fuse. Of course if you make a habit of this, your cord could get to be quite short :-). Battery powered yard equipment and power tools have improved greatly over the years. Some of the newer models are quite capable of cutting a modest size yard (e.g., 1/4 acre, manufacturers specifications may still be a bit optimistic) on one charge with ample power for moderately thick grass. But, there is quite a bit of variability in cutting performance and battery life so shopping around, consulting Consumer Reports, and making sure you get a return option if you are not satisfied are all well worth the effort - to save effort in the long run. It is interesting, however, that quite capable battery powered tractors for example, have been around for a long long time. See the section: "Comments on electric mowers" for more information. Having said all that, the fact of the matter is that the vast majority of lawn mowers used for modest or larger lots are gasoline powered. Of course, if you have a postage stamp size or even a small suburban lot, a manual reel mower may be your best choice - and you get some good exercise as part of the deal as well. Also see the comments in the Chapter "Items of Interest" on electric and manual mowers.
Depending on the size of your lot, glowing conditions, and your energy
level, one or more of the following options will fit you like a glove:
* Reel mowers - manual type are still available and suitable for small lots.
Safe, non-polluting, quiet, low maintenance, and low cost substitute for
aerobic workout.
* Rotary mowers (gasoline powered) - Most common type, convenient, relatively
low maintenance, some pollution, generally noisy.
* Rotary mowers (electric, AC line or battery powered). Convenient, low
maintenance, non-polluting, usually quieter than gasoline powered mowers,
limited by cord length or battery charge.
* Teenage kid - low maintenance but variable performance and possible
reliability problems.
* Landscaping service - expensive but consistent and may occasionally mow your
valuable flower bed as weeds by mistake.
* Cow, goat, or other herbivore - mowing performance quite variable, fencing
required, excellent source of fresh fertilizer. The extended warranty is
essential! :-)
The first two of these are described in more detail is subsequent sections.
Large mowers (those which carry you) may be of either the rotary or reel type,
usually gasoline or diesel powered but some electrics have been produced. For
information on riding mowers, lawn tractors, garden tractors and estate
tractors (also known as compact diesel tractors), see the Small Tractor FAQ.
Consumer Reports regularly provides reviews and ratings of most common types
of lawn mowers. These articles are a good place to start as they include
a great deal of the basic information needed to decide on the lawn mower type
best suited for your property. They compare a selection of typical models
based on features, safety, price, and their tests of performance and operator
convenience. If you do not subscribe to Consumer Reports, your local library
will likely have access to several years of back issues.
* Self propelled lawn mowers (gas, electric), June 1996, page 44.
* Lawn Mowers (gas, electric, manual), June 1995, page 394.
* Riding Mowers and lawn tractors, June 93, page 388.
For even more advice, see Consumer Reports Books' Yard and Garden Equipment
Buying Guide. It is sold at bookstores and newsstands and is also available
directly from Consumer Reports Books using the order form in the back of every
issue of Consumer Reports.
These may be manual or engine powered. A spinning set of sharp spiral cutting blades working against a fixed 'bedknife' snips off grass like a scissors. In principle, reel mowers can produce an exceptionally consistent manicured lawn. However, small reel mowers may have serious cutting height limitations and also result in a wavy uneven appearance. * The common (some would say old fashioned) manually operated push reel mower is simple in construction, easy to operate (if you have the energy), safe, quiet, compact to store, and modern ones in particular are quite light in weight. However, blade sharpening is something best left to an expert. If your lot is small and/or you like the exercise, a manual reel mower may be for you. * Small engine powered reel mowers do exist but I do not know if they are still readily available. I have seen them at garage and estate sales. While I have never seen an electric powered reel mower, this would seem to make a lot of sense for battery operation as the power requirement of a reel mower are much less than for a rotary type. * Professional landscapers often use large engine powered versions of these machines which may have multiple cutting heads and are self propelled, ride-on, or pulled behind a tractor. See the Reel Mower FAQ for additional information on this type of beast.
These may be gasoline or electric (AC line or battery) powered. A spinning blade or blades whirls at the selected cutting height and lops off the tops of you grass by side impact. This is most definitely brutal treatment of your poor defenseless grass! The length of the cutting blade determines how much of a swath is cut on each pass - typically 18 to 24 inches for a walk-behind mower; up to 36 inches or more for a riding mower. Mowers with large swath widths may use two or more smaller blades instead. The uniformity, consistency, and just general appearance of a lawn mowed with a rotary lawn mower is not quite up to the standards of that of a professional reel mower. You will never get the perfect manicured look though some models may come close. However, the simplicity, lower cost, and need for less and more easily performed maintenance will generally overcome the desire for perfection unless your lawn is featured regularly in "Better Homes and Gardens" magazine. Gasoline powered rotary lawn mowers are by far the most common type used by homeowners and many professional landscapers as well. Most walk-behind mowers use a manual recoil (pull) starter though electric start is available on more sophisticated (and more expensive) models and generally standard on riding mowers and lawn tractors. The main disadvantages of a gasoline powered mower are the need to deal with the handling and storage of gasoline and routine engine maintenance at the end of the mowing season to assure easy starting next season and to prolong engine life. However, most of this is pretty straightforward. See the section: "General preventive maintenance". Small gasoline engines also do contribute to air pollution but new mowers must meet more stringent EPA requirements as of September, 1996. Electric rotary mowers are also available in both plug-in and cordless (battery powered) versions. However, since gas mowers are generally more powerful and not limited by the length of a power cord or charge of a battery, they continue to dominate the market. Electric mowers are, of course, non-polluting but the electricity had to be generated somehow.
All rotary mowers manufactured within the past 15 years or so must have a dead-man control to stop the blade quickly (within a couple of seconds) if the handle is released or the operator falls off of the seat of a riding mower or lawn tractor. While not foolproof, this feature greatly reduces the chances of serious injuries due to accidental slipping or falling - or attempting to make adjustments while the blade is spinning. WARNING: Never defeat the dead-man control for any reason unless there is no chance of the mower starting. * For gasoline powered mowers, this means that the spark plug wire had been pulled and tied a safe distance (a few inches minimum) away from the spark plug terminal or the spark plug has been removed entirely. Even draining or detaching the fuel tank is no guarantee that the engine will not start as the carburetor often contains a few minutes of fuel reserve. * For electric powered mowers, this means that the wall plug has been pulled or the battery disconnected and the wire tied or taped to prevent any accidental contact. Always restore the dead-man control to normal operation before attempting to start the mower.
In addition to options with respect to gasoline or electric power, rotary
mowers can be classified based on such things as: walk-behind vs. ride-on,
to bag or not to bag, and rear or side discharge or mulcher:
* Walk-behind mowers may be either of the push type - you provide the
power to move the mower; the engine or motor spins the blade - or
self propelled where the engine (usually only for gasoline types)
drives the front wheels via a fixed or multiple speed transmission.
Typical engine power is from 3 to 6 HP with the trend nowadays toward
the higher end of this range especially for self propelled models.
* Side discharge mowers eject the grass clippings from the right side
(usually) to the rear. These are probably the most common type in
use today due to their low cost. Some perfectly serviceable new mowers
of this type sell for $100 or less. Optional grass catcher bags permit
some of these to be converted to side-baggers if desired but the bags tend
to be much smaller and thus less convenient than those for rear bagging
mowers to prevent them from becoming side-heavy when the bag fills up.
* Rear baggers eject the grass clippings into a bag mounted behind the
mower. Bags tend to fill quite quickly - especially if you keep putting
off your mowing assignment - and need to be emptied or changed frequently.
The weight of the grass clippings in the bag also contributes to the
mass of the mower - which you have to push if it is not self propelled.
WARNING: Rear baggers should never be operated without a bag unless the
opening is fully blocked or the proper deflector is installed. Grass
cutting performance will then be similar to that of a mulching or (side)
discharge type mower respectively but since this is a compromise, the
resulting appearance of the cut lawn may suffer.
* Mulching mowers do not discharge the clippings but continue to chop them
up under-deck until they are small enough to cease being sucked up by the
airflow. The best will result in almost no detectable evidence of grass
clippings though the worst may leave big clumps behind. The appearance of
the lawn from a mulcher may be as good or very nearly as good as that from
a bagger but this is not assured. Some mowers - both discharge and bagging
types - can be converted to mulching mowers by using a special cover to
block the discharge port and possibly a different mulching blade.
Side discharge and bagging mowers can often be converted to mulching with
the use of a mulching kit which includes a means of blocking the discharge
port and possibly a special mulching blade. However, performance of one
of these may not be as good as that of a mulching mower since the airflow
requirements differ and these are largely determined by the design of the
deck.
* Riding mowers are basically larger versions of the self propelled bagging
mower with a seat for the operator, steering wheel, and more controls for
cutting rate and forward speeds. The engine is typically in the 8 to 10
HP range and is mounted in the rear beneath or behind the seat.
* Lawn tractors may be even more sophisticated than riding mowers with
larger blades and additional options for non-lawn mowing tasks. The
engine is higher power - 12 to 18 HP or more - and is mounted up front
under a hood as in a real tractor.
WARNING: Most lawn mowing accidents result from reckless or careless use
of riding mowers and lawn tractors, not walk-behind mowers. These are not
as stable as an automobile especially when their large bags are full of
heavy, wet, grass clippings and may tip over on inclines that would not
be a problem with someone in control of a walk-behind lawn mower. They
are best and safest for use on large flat open lots. A walk-behind mower -
perhaps even a manual reel mower - should be used for sloping or irregular
areas and for mowing or trimming around obstructions like trees, shrubbery,
landscaping timbers, posts, fences, planters, boulders, and so forth.
If this is a new purchase, you should have a users manual - READ IT!!! Above all, understand the very important SAFETY information. If there is some 'simple assembly required', take your time and follow the instructions step-by-step. Despite the apparent efforts of the designers of the mower and the manual writers to make everything as obscure as possible, it will probably go together without undo difficulty if you use the proper tools. With some, all you need to do is unfold the handle taking care not to pinch any control cables - oops - and you are ready to go to work. Happy times are here again!! IMPORTANT: For 4 stroke engines, make sure there is oil in the engine!!! Learn how to check it and fill it to the proper level if there is none or it is low. See the section: "Checking the oil". WARNING: Running an engine without oil can ruin it in a few minutes and your warranty will not likely cover such stupidity. Since the lawn mower may be shipped without any oil, it is your responsibility to check this and then add the proper amount of the correct type of oil to the crankcase!!! For 2 stroke engines, special oil (not the usual 10W-30/40 type motor oil, nor WD40 or 3-In-One!) must be mixed with the gasoline in the correct proportions IN THE GAS CAN - not the fuel tank of the mower! See your users manual! Forgetting to use the proper mixture can ruin a 2 stroke engine in a matter of minutes and your warranty will not likely cover such stupidity. Adding the oil to the fuel tank is not recommended because thorough mixing cannot be assured. If you have yard equipment with both 2 stroke and 4 stroke engines, clearly label the two gas cans to indicate which equipment each is used in.
Use only fresh unleaded gas. Regular octane rating (87) is fine - small engines operate at relatively low compression ratios so knocking should not be a problem. There is likely no benefit to using anything higher. Gas that is over a month old may have lost some of its more volatile fractions resulting in hard starting, possible varnish formation, and other undesirable effects. At the end of the season, dump the unused (unmixed) gas into your car (preferably when its fuel tank is at least half full so your old gas gets mixed with fresh gas). This way you won't be tempted to use it at the start of the next season. For 4 stroke engines, gasoline is used as-is since there is a separate oil supply. For 2 stroke engines, you must mix the proper amount of the correct 2 stroke engine oil (outboard motor oil or whatever is recommended by your engine's manufacturer). Fill your '2 stroke mixture' gas can with about half the amount of gas you are preparing and add the proper amount of 2 stroke engine oil. Put on the top and slosh this around to thoroughly mix the oil in with the gas. Then add the remaining gas to the total amount for which your oil measurement was made. How do you tell if a lawn mower you just inherited has a 2 stroke or 4 stroke engine? The vast majority are 4 stroke - look for an 'oil filler cap'. On many, this is clearly marked with words like 'oil' or 'oil fill' or with a suitably ambiguous icon. Removing it will reveal a dipstick. (Note that unlike the engine in your automobile, this is both the test and filler location.) However, on more basic models, it may be near the base of the engine and be unmarked. In addition, there will generally be markings as to the need for the gas/oil mixture somewhere on the cover. The only major manufacturer of lawn mowers I know of that has used 2 stroke engines in recent designs extensively is Lawnboy. If you are unsure of the correct mixture ratio - they typically range from 16:1 to 32:1 gasoline:oil by volume - 16:1 is probably a safe choice. The worst that can happen is that the spark plug may be more likely to foul (and you will pollute more than necessary) but at least you won't risk damaging the internal parts from lack of oil. It is of course best to determine and use the recommended mixture ratio.
Your nearest auto service station will sell you small quantities of gasoline. As noted in the section: "Safety guidelines", you must use an approved gasoline safety can which will be red in color. These come in sizes from 1 to 5 gallons or more and may be made of plastic or metal. A convenient size is 2 to 2-1/2 gallons. The fuel tank on a typical walk-behind mower will be between 1/4 and 1/2 gallon. Warning: When filling your gas can, place it on the ground a few feet from your vehicle - never fill it inside the trunk or truck-bed. See the section: "Where to fill gas can?". However, a gallon of gas goes a long way with a walk-behind lawn mower. I don't have exact numbers but a gallon will probably do an acre or more of mowing (assuming you aren't chopping foot high grass!). (From: Faron Faulk (faronf@microsoft.com)). "Not to nitpick, our lot is .82 acre and I can mow it with 1 mower tank full of gas. So, for my mower (a Lawnboy 2 cycle) I can probably do at least 4 acres with a gallon of gas (since i can get 5 or more fillups with one gallon). 5 gallons of gas has lasted me most of the summer (including weedeating)" If you must transport gasoline in a vehicle, make sure the container is secured in an upright position and tightly capped (both the filler spout and vent openings). Provide adequate ventilation so there can be no possibility of fume buildup in the trunk or passenger compartment.
Always remove the gas can from vehicle before filling it. In addition to common sense 'what ifs' with respect to spills and fume buildup, there may be an added risk do the the buildup of static electricity: Also see the section: "Chevron technical bulletin on explosion risk when filling a metal gas can". (From: Joyce (joduren@ix.netcom.com) Please be careful about filling the gas can. I saw something on one of those PBS How to do it shows (or was it in the newspaper?) that said that people are filling their plastic gas cans with them still in their trunks or hatchbacks. They said this is dangerous because the can isn't grounded or something and a static electricity spark could make the thing to explode.
"Isn't there a gasoline additive you can add to the gas which will keep it 'fresh' for up to 24 months? I've seen it at Home Depot, though have never used it. I think a tube was less than $1.00." (From: Floyd Reed (floyda@ix.netcom.com)). Being an old small engine mechanic from way back, I suggest that you don't use any additives to keep your gasoline 'fresh'. Dispose of old gasoline (end of season) by dumping it in the (nearly full) fuel tank of your car, then refill your gas can at the beginning of the mowing season. It should last you the season. With this method, you spend no extra on additives (that are no good for an engine), you don't waste 'old' gasoline, and you don't dump raw gasoline into the environment. (From: Dan Weise (dan_yz@cin.net)). I have found the commercial product Stabil the best thing since sliced bread. It prevents the gasoline in the gas tank from gumming up. I'm too busy to run around emptying gas tanks in the fall. Instead, I shoot in a squirt of Stabil, run the engine for 5 minutes, shut the gas valve off (unless it's a suction carb mounted on the gas tank) and the engines start next spring. That was *not* the case before Stabil. I can't count the number of times I've disassembled a carb and sprayed Gumout trying to unclog the main jet or the idle jet. Or had the float stick down and flood everything in sight. All because of gummy gasoline. I've used Stabil for about 10 years with great success. I also use that Slick 50 teflon stuff, but have no idea whether it does any good or not. But for the investment in an engine, I can't see that it hurts. The intermittent duty of many engines makes them more vulnerable to oil run-off than vehicles that are used daily.
Note: while written with gasoline powered rotary mowers in mind, most of these comments apply to electric models as well. * Reread the section: "Safety guidelines" particularly with respect to the storage and handling of gasoline. * Make sure you understand the operation of your mower. In particular, how to stop it! On most modern inexpensive mowers, the engine should stop as soon as a dead-man safety bar is released. This is supposed to both kill the ignition to the engine and apply a brake to the blade (usually to the flywheel). On more sophisticated machines, releasing the bar disengages the blade but does not stop the engine - do you know how to stop the engine? * Check, and if necessary, set the cutting height. (I will leave it to the gardeners to determine optimal height. Around 2 to 2-1/2 inches is probably acceptable unless you are mowing a putting green.) This is usually accomplished either with levers on each of the wheels or by removing and reinstalling each of the wheels into one of several holes. A few mowers use a single control for all wheels - very convenient. Always make sure all (4) wheels are set at the same height. * Check the oil and if necessary. top it off. * Remove any obstacles or debris in your path - rocks, stones, wood blocks, branches, etc. These are a safety hazard and killers for your lawn mower. If the blade hits something small, it can become a high speed projectile traveling at up to several hundred feet per second - this is a substantial fraction of the muzzle velocity of a handgun. If the blade tip contacts something larger, the engine will stop and serious damage may be the result. See the section: "Why you really don't want to attempt to move an immovable object". In some cases, obstructions like tree roots cannot be moved. In this case, you will either have to mow around them or raise the cutting height of the blade to clear. * Make sure all protective devices are in place on the mower. Rear baggers must have a bag or proper cover installed (many are automatic). Side baggers must have a bag or deflector installed. Change bags only with the blade stopped - and preferably the engine stopped as well. * Wear proper clothing and sturdy fully enclosed shoes with non-slip soles. Avoid mowing when the ground is wet and slippery. * Wear proper eye protection - plastic eyeglasses or safety glasses - to to protect your eyeballs from flying debris. * Use some kind of hearing protection - ear plugs or muffs. Even just a wad of cotton or tissue will greatly reduce the noise level to your ears. * Keep curious kids and pets a safe distance away. * Avoid mowing a highly sloping area in the up and down direction as the mower can slip or you can slip. Even with the safety blade brake, it takes a couple of seconds for those knife edges to come to a stop. If you must mow such an area, do it from side-to-side and be careful of side-bagging mowers that may tend to tip over particularly when their bag is filled with grass clippings. Better yet - only plant rocks on highly sloping areas!
Most mowers and other small pieces of gas powered yard equipment use a self retracting recoil type starter. You pull on a handle attached to a cord wound around a one-way clutch affair. Pulling on it rotates the engine's crankshaft and the clutch allows the engine to run without pulling you back into the mower! If yours has an electric starter, then you don't need to tug on anything - plug it in and push a button or turn a key. Of course, finding an outlet at the far end of a large yard may prove to be a challenge. With larger equipment like riding mowers, power is usually provided by an on-board rechargeable battery. In either case, there will be some kind of backup recoil or rope starter should the electric start be unusable or inconvenient. For the following, we will assume you pull a self-retracting starter rope. With an electric starter, replace the words: 'pull...times' with 'crank for several seconds'. Move the mower or other equipment to the place where it will be used - no sense in dragging a chugging lawn mower through the neighborhood. Position it on a solid level surface. Make sure there are no loose stones, twigs, branches, logs, etc. underneath to get sucked up and thrown about once you succeed in getting the engine started (if you ever do). When attempting to pull on the starter cord, it may be helpful to put one foot on the mower deck to brace it. Whether this is needed will depend on the design of your mower and in what direction the cord exits from the starter. You or the starter motor supplies the power to get it started. However, at the low speed of starting, special modifications may be required to the fuel system for the engine to catch. These may take one of the following forms: * Primer - a rubber bulb or pushbutton squirts a little extra gas into the intake pipe. Your engine manual will detail the procedure and number of 'pushes' required under various conditions - typically between 1 and 12. Too few and nothing will happen. Too many and you will flood the engine (excess gasoline will prevent it from starting). A typical starting procedure for an engine with a primer might be: - Set the throttle control (if any) to the START or HIGH position. - Push the primer 5 times. - Pull the starter cord once or twice (if it doesn't start on the first one). - If it still doesn't start, prime 2 more times. - Pull the starter cord again. - Set the throttle control to the desired speed once it starts. * Automatic primer - a chamber in the carburetor which fills with the engine stopped and provides an additional squirt of gas when starting. Automatic choke - temperature and engine vacuum control the fuel-air mixture. A typical starting procedure for an engine with an automatic primer or automatic choke might be: - Set the throttle control to the START or HIGH position. - Pull the starter cord once or twice (if it doesn't start on the first one). - Set the throttle control to the desired speed. * Choke plate - a control on the carburetor which partially closes off the air intake and forces additional suction to increase the amount of fuel drawn into the cylinder. Normally, the choke is closed when starting cold and gradually opened in the few seconds after the engine starts. It is left fully open once the engine is running and may not need to be closed when starting warm. A typical starting procedure for an engine with a choke might be: - Close the choke (usually on carburetor). - Set the throttle control (if any) to the START or HIGH position. - Pull the starter cord once or twice (if it doesn't start on the first one). - If it still doesn't start, open the choke half way. - Pull the starter several more times until it starts (hopefully). - Gradually open the choke to keep the engine running smoothly. - Set the throttle control to the desired speed. If the appropriate procedure is not successful, the engine may be flooded. You can give it 15 minutes or so for the gas to evaporate and try again or, if there is an IDLE or LOW speed position, open any choke and pull the rope several times in this position which should clear out the excess gas. Then repeat the recommended starting procedure. If none of this works, you may have a starting problem and should refer to the section: "Lawn mower will not start". Probably, you forgot to fill the gas tank!
On most inexpensive lawn mowers manufactured within the last 10 or 15 years, releasing a dead-man bar on the handle both kills the engine and applies a brake to the blade (well, actually the flywheel of the engine). In this case, there is nothing to think about - just release the handle and it will stop within a second or two. These are quite reliable. The usual problem is that you forget to engage the dead-man bar and attempt to start the mower despite the basic fact that this is quite impossible! More expensive equipment will have a blade brake clutch meaning that while there is still a dead-man bar but instead of killing the engine when released, it disengages the blade (clutch) and brings it to a rapid stop (brake). This is more convenient especially with a balky engine. There will then be a separate engine stop switch - possibly combined with a speed/throttle control. Equipment with an electric starter may have an ignition switch just like an automobile and there will be three positions: STOP, RUN, START. Some older equipment just has a stop contact that grounds the spark plug. Pressing on a lever connects the spark plug terminal to the engine chassis and kills the spark. While this is fairly reliable, it may be a momentary contact meaning that the engine may be on a hair trigger and even rotating the blade a fraction of a turn may cause the engine to take off again. Thus, disconnecting the spark plug wire or removing the spark plug is even more critical when working on this sort of equipment.
What should you do if the engine stop switch has no effect? Probably the safest and surest is to use a wooden stick to pop the spark plug connector off of the spark plug terminal. This **will** stop the engine. The most likely cause of such misbehavior is a stop wire that has become disconnected or has broken. This is easily remedied.
Here is what you should do at the end of the mowing season: * Change the oil. If you do nothing else in this list, at least change the oil. Old dirty oil will shorten the life of your engine and affect its starting and running performance eventually. * Drain the fuel tank and discard this gas. Put any fresh (unmixed) gas remaining in your gas supply can into your car so you won't be tempted to use it next season. Then run the mower until it stops from lack of gas. (This will use up the gas still remaining in the carburetor. This is particularly important for float type carburetors). This will take at most a couple of minutes. Also see the section: "Additional comments on winterizing - draining vs. use of fuel stabilizer" for more info. * Inspect the air filter (and fuel filter if present). If dirty or clogged, clean or replace as appropriate. * Remove and inspect the spark plug. The curved electrode and tip should be smooth and light gray or brown in appearance. If they have deteriorated or are damaged in any way, replace the spark plug. Engine repair books usually recommend replacing the plug in any case - they are inexpensive, under $2. Use the proper small engine spark plug - not one you found in the corner of your toolbox or removed from your automobile! A bad spark plug is a major cause of a hard-to-start engine. Check the spark plug gap (new or used) with a feeler gauge - it should be .030" for most small engines. Carefully bend the curved electrode to adjust - do not file the center electrode! * Squirt a teaspoon or so of fresh engine oil into the spark plug hole so that it coats all sides of the cylinder. WD40 will work as well since its purpose is protection and not lubrication. Then crank the engine a couple of times to distribute it. The oil will protect the cast iron cylinder liner and piston rings from rust during the off-season. * If you reinstall the old plug, it is generally good practice to replace the metal washer. Install the spark plug finger tight and then tighten another 1/2 to 3/4 turn or to 15 to 30 ft-lbs with a torque wrench using the proper deep (spark plug) socket. * Clean above and below deck to remove dirt, leaves, and other debris. Pay particular attention to the area around the cylinder under the shroud (blower housing). Remove any leaves or other debris that might impede the all important air flow. * While underneath, inspect the blade for serious damage that would require resharpening or replacement. It doesn't have to be honed like a scalpel but there should not be too many deep nicks and it should not wobble noticeably or be bent or have bent or distorted tips. * If you have a battery for electric start, make sure the water reservoir (if not the maintenance-free type) is topped off, the terminals are clean and tight, and that it is fully charged. * Put a light coating of oil on any exposed unpainted steel parts. Check any front wheel drive components - chains, idlers, pulleys, and clean and lubricate if necessary. Dribble a few drops of light oil into any throttle, choke, safety interlock, or other cables. * Store the mower in a dry location supported off of the floor on wood blocks if there is any chance of flooding. Then, when it comes time to start mowing again (yes, I know, you can't wait), all you should have to do is add fresh gas (don't use last season's). The mower should start on the first (well, maybe, second) pull. There may be some white/blue smoke for a few seconds from it burning off the oil coating on the cylinder walls but this should quickly disappear. Here is another recommendation: (From: Bill Harnell (bharne@adss.on.ca)). Change the oil at the *end* of the season. No need to leave the acid charged oil in the crankcase over the winter to corrode the engine. Then add a couple of teaspoons or so of Stabilit to the gas tank. Run the engine for approximately 5 minutes and while you're at it, inject some fogging oil through the carburetor to thoroughly coat all of the interior surfaces. Directions are provided on the fogging oil container. Wipe the frame and handle with an oily cloth and oil all pivot points lightly. Clean the crud from under the deck - you do that frequently all summer - right? Remove all the grass clippings from around the flywheel and the cylinder fins. Then store it in the shed or garage. It will start on the first or second pull every spring. BTW, you should be able to get both Stabilit and fogging oil at any reputable engine service center.
The proper amount of oil is critical to the happiness of your engine. Too little and it may overheat, cause excessive wear, and in extreme cases (but not unusual), cause engine parts to seize and fail - very expensive. Make it a habit to check the oil regularly. Doing this after about every 5 hours of operation is generally recommended. More frequent checks - such as before each time you mow - are fine as well. A typical small engine in reasonably good condition does not use up a lot of oil but checking oil is easy and will not hurt. Oil should be checked when the engine is cold or after waiting 10 minutes for it to drain back into the oil sump after running the engine. * Place the mower on a level area. * If there is a dipstick - remove it, wipe it with a rag, and then reinsert it as directed on the information sticker or on the stick itself - usually threaded fully back in place and then removed to read. If the level is below or near the empty mark, slowly add the proper new oil to bring it up to just below the full mark. * If there is just a filler plug near the base of the engine, the correct level is just below the top - almost to overflowing. If lower than 1/4" or so below the lip, add new oil to top it off. (There may be exceptions to this but filling to near the top should be safe if you do not have your lawn mower engine manual handy.) If the oil level is high - you just bought the lawn mower or were careless in filling it last time - drain enough oil to bring the level back down to the full mark. Too much oil can result in problems as well - oil spraying out of various orifices or getting into other places where it should not be like the combustion chamber. If you find the oil level over the full mark or higher than it was before, gas may be leaking into the oil due to a flooded carburetor - a stuck inlet needle or bad float. If this is the case, the oil will need to be changed once the underlying cause of the leakage is determined. (This is only likely with float type carburetors such as those used on the Tecumseh engines used in a variety of Sears/Craftsman models equipment. If the oil is very low and you have been performing regular maintenance, there may be a leak or your engine may need a ring job. Excessive oil under the deck - on the shaft or blade adapter - would indicate a bad bearing or oil seal. Noticeable blue smoke while running would indicate that excessive oil is getting by the rings into the combustion chamber. Typical oil capacity is just over 1/2 quart (usually about 1-1/4 pints).
For the common 4 stroke engines such as Briggs & Stratton or Tecumseh, you don't need to buy specially high priced engine oil. The type likely used in your automobile will work fine and will be much less expensive. Although small engine manufacturers may recommend SAE 30 oil, they usually also state that 10W-30 or 10W-40 are acceptable substitutes - and these are what your car probably uses. New oil should have at least the SG rating though if you have some SF in your garage, that will be fine also (for your lawn mower, not your car!). However, there are situations like equipment that must run in extremely cold weather (probably not a problem with grass mowing!) where specific alternative oil recommendations should be followed. The capacity of a typical small engine is just over a 1/2 quart. This will probably cost you about 50 cents - a very worthwhile investment! However, some people do swear by synthetic oil. I remember it worked pretty well on my bicycle as well :-): (From: Daniel Pope (dpope@l-a-net.net)). Synthetic Motor Oil in the crankcase and Marvel oil in the gas is the only way to go! I have a $1,900 MTD tractor style mower with B&S engine (L head twin). It has over 800 hours and 9 years on it and I mean rough hours (bahaya grass and hot weather). The engine does not use a drop of oil (changed every 30 hours) and the compression is the same as when new. These other guys can have there $5,000 fancy mowers. I'll use that money to buy a truck.
If you don't do anything else to prolong the life and happiness of your small engines (and your automobile, for that matter) it should be an oil change at the recommended interval. Oil loses its lubrication and cooling effectiveness with use and this will gradually take its toll on your precision engine parts. Even a simple lawn mower engine is machined to very precise tolerances and any contamination will increase wear. Ultimately, its performance - starting and running - will suffer and its life will be shortened. Since there is typically no oil filter, all the grit, metal particles, and other undesirable stuff continues to circulate with the oil to find its way in between precision engine parts. For small engines, the oil change interval is usually specified to be about 25 hours of use. More frequent oil changes may be desirable if the equipment is operated in an extremely dusty environment. A typical mowing season for a modest size lot is around this amount of time so an oil change once a season is probably satisfactory. I recommend this be done at the end of the season so that the old contaminated oil does not sit in the crankcase during the winter months and you will not (conveniently) forget to do this at the beginning of next season when you are eager to get at that straggly lawn.
The oil change procedure is a lot simpler than for an automobile as everything is readily accessible and there is no oil filter to worry about. * You will need a funnel, low wide container or drain pan for the used oil, and a container like a plastic milk jug for temporary storage if the used oil for disposal. * Spread adequate newspaper on the ground to collect any drippings. * Run the mower for about 2 to 3 minutes to allow the oil to circulate and warm up so that it is less viscous and will flow more easily. Stop the mower. * If the fuel tank is less than about 1/3 full, then you will probably not have any problems, otherwise you will have to drain some gas or remove the fuel tank so that gas does not spill out of the breather hole in the cap. * If there is an oil drain plug, you can use this to drain the oil. However, it is usually more convenient to just turn the mower on its side, carburetor side up. This is usually acceptable for the short time that will be involved. Immediately check for any oil leakage - if there is any, we will need to avoid tipping the mower as much - look for the drain plug. * Wipe around the oil filler cap with a clean cloth or paper towel to remove the dirt and grime that has likely collected there. The oil filler will either be on or near the bottom of the engine or at the top of the shroud (Eager 1 type). If it is not right at the bottom, there will be a dipstick attached to it. * Place your wide mouthed drain pan under the oil filler cap and remove the cap. The oil will flow into your pan. Let it continue until the dripping stops - probably 10 minutes or so. * Set the mower upright on a level surface. Wipe any drips on the engine and deck up with a clean rag or paper towel. * Use the recommended oil for your engine. SAE30 is usually specificed by the engine manufacturer but they will usually state that 10W-30 or 10W-40 (SG rating) are acceptable substitutes. These 'multi-weight' oils are widely available and inexpensive. Typical small engine oil capacity is just over 1/2 quart. Start low and incrementally add oil until just below full on the dipstick or at the top of the oil fill hole if there is no dipstick. DO NOT overfill. Give it time for the relatively viscous oil to find its way into the crankcase. Tipping the mower back and forth a bit will help this process. * Replace the filler cap. Wipe up any additional drips. * Start and run the engine for a couple of minutes. Wait a few minutes, then recheck the level. Top it off if needed. * Transfer the used oil from your drain pan to the storage container and dispose of it in an environmentally safe manner.
The blade in a rotary lawn mower doesn't need to be sharp as a carving knife or scalpel but serious dents and nicks will result in a less than perfect lawn (to say the least!). In addition, a seriously unbalanced blade can result in excessive vibration and eventually, possible internal damage as well. First, drain the gas or remove the gas tank. If you will be filing steel, you get sparks. Sparks are not the greatest thing to have around gasoline vapor. Enough said. Disconnect the spark plug wire and tie it safely away from the spark plug or remove the spark plug entirely. Turn the mower on its side. CAUTION: Immediately check for oil leaks at the oil filler pipe or elsewhere. If there are any, you will need to work on the mower just propped up by 45 degrees or so. Or, use this as a good excuse to perform an oil change and drain the oil (even if the engine is cold, most of the oil will drain out but it will take a little longer). Just don't forget to refill the crankcase with fresh oil once you have completed work on the blade! Check that the blade isn't bent. Locate a reference point on one side and note the height of the blade tip at that location. Rotate the blade 180 degrees and check the height of the opposite blade tip. There should be no significant difference - say no more than 1/8" or so. If it is greater, the blade is bent or the crankshaft is bent. Either will require further investigation as running the mower under such conditions will probably result in excessive vibration and can be dangerous. Assuming this is fine, inspect the blade: Slight nicks and dents can be cleaned up with a file while the blade is still installed on the mower. Unless you have run into a curb, this is probably all that is needed on an occasional basis. Removing this small amount of metal will also not unbalance the blade enough to worry about. Refer to the section: "Non-violent blade removal" if it needs to come off the mower. If the damage is severe, consider replacing the blade entirely - they are not that expensive (usually under $10). Otherwise, you can use a file, a bench grinding wheel, or a grinding wheel mounted in an electric drill (there are special attachments for this specific application). Since the rotating blade also contributes to the proper air flow, you do not want to upset the shape. Grind in such a way that the original blade angle is preserved. It doesn't need (or want) to be razor sharp. A 1/64" edge is fine. Anything finer will quickly be dulled by little bits of stone and dirt in any case. Safety is not the main concern here - if any part of your anatomy contacts the whirling blade, you **will** be in trouble no matter how dull or sharp the blade might be! Attempt to remove approximately equal amounts of metal from both ends and in roughly similar areas if possible. If there are a few large nicks, it isn't necessary to remove them completely - your lawn (and neighbors) will never know the difference. Check the balance by positioning the blade at the center hole location on a pencil or other rod - you don't need a fancy blade balancer but can use one if you like. If it tips one way or the other, remove more material from the heavy side a little at a time. Replace the blade along with all its mounting hardware. Make sure you get all parts in the same relationship as they had originally. The blade must have its sharpened edges pointing downward. Don't forget the install the key if it is separate and DO NOT substitute a hard steel key for the soft metal one that should be used. See the section: "Why soft metal keys must be used". If the locking key or blade adapter key appear damaged, replace it.
For just some minor touch up, there is no real need to remove the blade. For major grinding and balancing, removal will be needed. Removal will also be required to inspect for a damaged or sheared blade lock key and to replace it if necessary. In either case: disconnect the spark plug wire and tie it safely away from the spark plug terminal (several inches minimum) or remove the spark plug entirely to prevent accidental starting. If the nut holding the blade on is just on very tight, use a block of wood to prevent the blade from turning. Use a good quality socket wrench or box-end wrench of the correct size - an adjustable or even open-end wrench may not be enough. The nut usually unscrews counter-clockwise. However, check this out first! A careful inspection of the threads on the end of the crankshaft will reveal the direction. Or, determine the direction of rotation which will be designed to tighten, not loosen the blade. Most, if not all, single blade mowers rotate the blades clockwise as viewed from above which will therefore use a normal right-hand thread nut. CAUTION: Make sure that if the wrench slips, your flesh will not contact the blade or other sharp sheet metal - liberal use of rags or newspapers is a good idea. Arrange your position and the mower so you are pulling towards you - this is a more stable controllable arrangement. (From: Graduate student of school of hard knocks.) "I'd wish I'd read this a few years ago. I used an open-end wrench and it 'flexed' off of the bolt. Needless to say, my next week wasn't a lot of fun with 10 stitches in my hand." Use some penetrating oil (e.g., liquid wrench or WD40) on the nut and threads if there are signs of rust or corrosion. Allow it to soak in for a few minutes before attempting to remove the nut. You will prevail. A hammer or other more violent approaches should not be needed. Once the nut is loose, unscrew it the rest of the way by hand and remove any washers or mounting plate and note their exact position and orientation. The blade and adapter should come off easily. Some penetrating oil (e.g., WD40) may help if it is difficult to remove. If your adapter/blade doesn't pop off after removing the nut or bolt, it may be mounted using a taper like the flywheel. This is somewhat unusual on a walk-behind lawn mower but might be present on a larger machine like a lawn tractor. A wheel puller is best for dealing with this situation but first see if it isn't just gummed up or rusted in position - try the WD40. Inspect the key or locking tab for damage. You may have: * A rectangular blade adapter with a welded-on soft metal ring with a tab protruding into a slot in the crankshaft. * A blade adapter that locks to the crankshaft with a rectangular or D-shaped (Woodruff) soft metal key. If the adapter's tab is broken off or the key is sheared or damaged, then replacement of the entire blade adapter or just the key (depending on your mower's design) will be needed upon reassembly. For now, if you will be sharpening the blade, replace all the hardware in the correct positions (except the blade) and finger tighten the nut so you won't lose anything. WARNING: Do not install a hard steel key in place of the recommended blade lock key as you will lose the protection that the soft metal provides and the next incident may be the last... See the section: "Why soft metal keys must be used". Once you have reground the blade or obtained a replacement, reassemble in reverse order and then tighten the nut to the proper torque. (From: Gib Gahan (gahan@esinet.net)). Another way to remove a stubborn blade is to take it to your friendly garage or tire changer and have them put an impact wrench on it. Saves knuckles, tempers, etc. Just don't put the blade back on without a touch of oil or anti-seize compound and of course, don't use an impact wrench!
If your engine is relatively new (made within the last 10 years or so) and has only one speed, then there may be no adjustments (like the one discussed in the section: "Cleaning Craftsman (Tecumseh) carburetors". It will either work or it won't - in which case it needs cleaning or parts replaced. Or your overhaul was less than 100% effective. You can tell if your carburetor is of this type as there will be no adjusting screws on the carburetor. For Craftsman types, there will be a solid hex nut on the bottom holding the float bowl in place. There may or may not be a primer button. For adjustable types, it is best to refer to your engine manual. However, here is the general procedure. Some of the specific numbers may differ for your engine, however. In all cases, before touching any adjustments, make sure you air filter is in place, and clean (or new). Fill the fuel tank about half full with fresh gasoline. There are three adjustments on a typical carburetor: * Main mixture - Bottom of Craftsman (Tecumseh) float carburetors. * Idle mixture - Side into body of Craftsman (Tecumseh) float carburetors. * Idle speed - Sets relaxed position of throttle plate. Initially, carefully and gently turn the two mixture controls in until they just seat. CAUTION: do not force them - you are not trying to tighten anything - as you will damage the needles and seats which will require replacement of the needles or entire carburetor. Then back them out 1 to 1-1/2 turns. Set the idle speed screw 1 to 2 turns beyond where it contacts the throttle plate. Refer to your engine manual for specific recommendations! These settings should allow the engine to start and run, though perhaps not entirely smoothly or with great enthusiasm. * Start the engine and allow it to reach normal operating temperature - a couple of minutes. Make sure any choke is off once it is started and running stably. This will also flush any old deteriorated gasoline from the carburetor! * With the engine throttle control set for the maximum recommended rpm, very slowly rotate the main mixture screw counterclockwise (loosen) until the speed begins to drop off due to too rich a mixture. Then, rotate the screw very slowly clockwise (tighten) until the engine begins to cut out. Very slowly means a fraction of a turn at a time - then wait a few seconds for the adjustment to have an effect. Note the number of turns between these two positions and set the screw in the middle of this range. * Repeat this procedure with the engine throttle control set to the idle or slow speed position but using the idle mixture screw instead. * If there is a high speed adjustment - possibly on the throttle control itself or the throttle control bracket, it is best to set it using a tachometer. However, it is possible to to a very good job by comparing the speed by ear to an identical type engine that is set correctly. See the section: "Setting engine speed". WARNING: if in doubt, set it low. It is better to end up with a scraggly lawn than bodily injury or a blown engine! * Set the idle speed adjustment just high enough that the engine idles smoothly and isn't about to cut out. A tachometer can be used to set it to specifications but there is no risk is just adjusting it to idle smoothly. * Test the engine under load. It should respond to load pickup immediately. An engine that dies is set too lean. An engine that runs roughly when picking up load is set too rich. Make a small adjustment (i.e., 1/8th turn) and test again.
Many inexpensive mowers don't even have a speed adjustment screw. Spring tension and the linkage to the governor set speed - period. Note that actual speed is rarely that critical for engine driven equipment as long as it is within safe limits. See the comments below on string trimmer speed settings. However, what options do you have where there is a need to set the precise engine speed? * Use a tachometer designed for small engines. If you do a lot of small engine work, this may be a worthwhile investment. For most of us, it would gather dust. * Use a tachometer designed for automotive engines. You may already have one of these if you do your own tune-ups. Sure, right, that went out of style about the same time as emissions controls! OK, maybe your father did his own tune-ups :-). Since an automobile engine spark plug fires on every other revolution of the crankshaft rather than every revolution as with most single cylinder 2 and 4 stroke engines, it will probably be necessary to multiply the reading by a factor of 2. (Even though there is a power stroke every other revolution for the 4 stroke engine, the ignition system is usually active on every revolution. However, there are a few exceptions to this rule.) * If you have electronic test equipment such as almost any oscilloscope or frequency counter, it is a simple matter to couple its input to the spark plug wire on its insulation (not to the plug itself!). Then, the speed is equal to the pulse rate for most single cylinder 2 stroke and 4 stroke engines. * Compare it by ear to another engine of the same type (2 stroke or 4 stroke) that is correctly set (i.e., you didn't muck with it!). This is actually a remarkably accurate way of setting the speed. For equipment where a shaft with a known speed ratio to the engine crankshaft is available (i.e., a power take-off or trimmer head), an optical stroboscope of one form or another may be used. You will just need to paint or tape some stripes on the rotating part to put under strobe illumination: * A fluorescent lamp powered by a magnetic ballast (not an electronic ballast) flickers at 120 Hz (in the U.S., 100 Hz in countries with 50 Hz power) and may be all you need to accurately set speed. For example, for something like a string trimmer which has a direct coupled hub, strobe disks with 2, and 3, and 4 radial lines will appear stationary under fluorescent illumination for 3,600, 2,400, and 1,800 RPM respectively. There can be ambiguity but if you are already in the ball park, this sort of approach may be all you need. * Use a stroboscope which is calibrated in RPM or Hz. You may be able to borrow one from a high school physics lab or Disco! * (From: Philippe Habib (phabib@netcom.com)). Go to a hobby shop that sells radio controlled airplanes. Plunk down $30 or so and get an optical tach. Paint 2 strips on the (crankshaft) hub of your equipment to simulate a propeller, and you're done. (From: J. Matthew Good (jmg14213@ix.netcom.com)). You shouldn't need a tachometer on a trimmer. Two stroke engines in the size and power range of line trimmers can't overspeed as they don't have the power with a line head installed. Just set the carburetor up so that it 'two-fours' at wide open throttle and you should be all set. If it needed to be adjusted with a tachometer, it would have some kind of governor on it.
The following chart lists a variety of common problems and nearly all possible
causes. Diagnostic procedures will then be needed to determine which actually
apply. The 'possible causes' are listed in *approximate* order of likelihood.
Most of these problems are covered in more detail elsewhere in this document.
While this chart lists many problems, it is does not cover everything that can
go wrong. However, it can be a starting point for guiding your thinking in
the proper direction. Even if not listed here, your particular problem may
still be dealt with elsewhere in this document.
(Portions of the following from: Chilten, Small Engine Repair 2-12 HP, (1)).
Problem: Engine will not start or is hard to start.
Possible causes:
1. Fuel tank is empty or shutoff valve is closed, or fuel line or
fuel tank cap vent is clogged.
2. There is water in the fuel.
3. Carburetor is overchoked.
4. Carburetor is improperly adjusted or needs service.
5. Ignition system or its wiring is defective or ignition switch is off.
6. Deadman or other cutoff switch is open or defective.
7. Spark plug is fouled, improperly gapped, or damaged.
8. Engine compression is poor.
Problem: Engine starts easily but dies after a few seconds.
Possible causes:
1. Fuel tank is empty or shutoff valve is closed, or fuel line or
fuel tank cap vent is clogged.
2. Carburetor is overchoked.
3. Carburetor is improperly adjusted or needs service.
Problem: Engine misses under load.
Possible causes:
1. Spark plug is fouled, improperly gapped, or damaged.
2. Breaker points are pitted or improperly gapped, breaker arm is
sluggish, or condenser is bad.
3. Carburetor needs adjustment or service.
4. Fuel line, fuel filter, or fuel tank cap vent is clogged, or fuel
shutoff valve partially closed.
5. Valves not adjusted properly or valve springs weak.
6. Exhaust ports blocked (2 stroke).
Problem: Engine knocks.
Possible causes:
1. Magneto is not timed properly.
2. Carburetor is set too lean.
3. Engine has overheated.
4. Carbon buildup in combustion chamber.
5. Flywheel is loose.
6. Connecting rod is loose or worn.
7. Cylinder is excessively worn.
Problem: Engine vibrates excessively.
Possible causes:
1. Engine is not mounted securely.
2. Blade or other driven equipment is unbalanced.
3. Crankshaft is bent.
4. Counterbalance shaft is not timed correctly.
Problem: Engine lacks power (possibly after warmup).
Possible causes:
1. Choke is partially closed.
2. Carburetor needs adjustment or service.
3. Ignition is not timed correctly.
4. Air filter is clogged.
5. There is a lack of lubrication.
6. Valves are not sealing properly.
7. Piston rings are not sealing properly.
8. Head loose or head gasket blown or damaged.
9. Exhaust ports blocked (2 stroke).
Problem: Engine operates erratically, surges, and runs unevenly.
Possible causes:
1. Fuel line or fuel tank cap vent is clogged.
2. There is water in the fuel.
3. Fuel pump is defective.
4. Governor is not set properly, sticking, or binding.
5. Carburetor needs adjustment or service.
Problem: Engine overheats.
Possible causes:
1. Magneto is not timed properly.
2. Carburetor set too lean.
3. Air intake or cooling fins are clogged.
4. Shroud or blower housing missing.
5. Excessive load.
6. Insufficient or excessive oil.
7. Improper oil viscosity (4 stroke) or mixture (2 stroke)
8. Valve clearance is too small.
9. Excessive carbon buildup in combustion chamber.
Problem: Crankcase breather passing oil.
Possible causes:
1. Too much oil in crankcase.
2. Engine speed is excessive.
3. Oil fill cap or gasket is damaged or missing.
4. Breather mechanism is dirty or defective.
5. Piston ring gaps are aligned.
6. Piston rings are worn.
Problem: Engine backfires.
Possible causes:
1. Carburetor set too lean.
2. Magneto is not timed correctly.
3. Valves are sticking.
This is probably the most common problem you are likely to encounter. The cause is very often the same - lack of maintenance. Note that the assumption here is that it cranks - the crankshaft and blade rotates in a normal manner but the engine never catches. Some larger (Briggs and Stratton) engines may have a low-oil cutoff switch which will stop the engine if the oil level is inadequate. However, this is not likely on a push mower. * In the case of a recoil starter, you are able to pull on the cord and the crankshaft with the blade rotates and it feels normal but the engine does not start. If it feels like nothing is engaging, than the starter mechanism or clutch may be broken. Of course, if the cord breaks, then the problem is obvious! * In the case of an electric starter, the engine cranks but never catches. If there is no response to the button or key, then the outlet may not be live, the battery may be weak or dead, or there could be a bad connection or bad starter motor. If the motor spins but doesn't engage the engine, the overrunning clutch or gear could be broken. If you are unable to pull the cord (or the auxiliary starter on one with electric start), there may be a clump of grass stuck between the blade and the deck or there could be serious internal damage, especially if you just encountered an immovable object. See the section: "Lawn mower will not start after the blade hit an obstruction". However, you didn't forget to engage the dead-man bar, did you? On most inexpensive mowers this safety interlock is needed to both enable the ignition system and release the blade brake.
Think: FAST - Fuel, Air, Spark, Timing. Diagnosing a balky engine is not difficult but a step-by-step methodical procedure will make it a lot less traumatic. Despite all the warnings, serious problems rarely develop on their own. Most likely, there is a simple, easily remedied cause.
Obviously, the engine won't run without gas! * Is there some in the fuel tank? If it is near the bottom, add enough so that there is no doubt about there being enough to reach the outlet pipe regardless of any slant on which the lawn mower is located. * Make sure any shutoff valve is open. * Check for a clogged fuel filter, if there is one. There may be a sediment catching screen at the bottom of the tank as well. * If you engine uses a primer bulb, does it feel like it is doing something? There is a distinctly different feel when it is actually squirting a little gas into the intake pipe. * If you are using gas from last season, discard it and start fresh. While old gas will usually work in an engine in good condition, this is not always the case, especially with one that has seen better days. The more volatile fractions evaporate leaving behind higher flash point gas. Why add another unknown factor to the puzzle? * There may be water in the gas. If the carburetor has a drain plug, operate it to rid it of the bottom layer which would have the water. If there is no drain, repeated pulling on the starter cord should eventually clear any reasonable amount of water. Once you have exhausted these obvious problems, determine if gas is reaching the cylinder as follows: Perform the normal starting sequence and then, assuming it shows no signs of wanting to start, immediately remove the spark plug. If fuel is reaching the cylinder, the spark plug should be damp with gas and there should be a very distinct odor of gas from the spark plug hole. If there is none, then there could still be a blockage in the fuel line or the carburetor may need cleaning. A flooded engine, most likely due to extended unsuccessful attempts at starting or a defective carburetor (float valve stuck open or gas-logged float) will result in inability to start as well and a distinct odor of gas. You might find raw gas coming our of various orifices - air filter as well as exhaust. (Note that in severe cases, enough gas gets mixed in with the oil to significantly increase the level in the crankcase and reduce the effectiveness of the oil. This will require an oil change.
The optimal air:fuel ratio is around 14:1. This must be lower for a cold engine and thus a choke plate or other means to increase the richness of the mixture is usually provided. A choke plate restricts air intake forcing more gas to be sucked into the cylinder. A primer bulb effectively squirts gas into the intake pipe to augment the normal carburetor action. Some carburetors have no choke and no primer but incorporate an small gas reservoir which fills when the engine is off and provides some extra when starting. To much air results in a mixture that is too lean, burns too quickly, and can result in engine damage over extended periods of operation. * Check that any choke is not stuck in the open position and not doing its job. * The carburetor may need adjustment or cleaning. Too little air results in a mixture that is too rich - there will be loss of power and possibly black smoke from the exhaust. This could be due to several factors: * Check the air filter. For testing, it can usually be removed to see if the engine will start. However, do not run it for an extended period of time without a properly functioning air filter in place. Some are designed to be washed and reused while others must have their elements replaced. * Check that any choke is not stuck closed. Though needed to start cold, if the choke remains closed, the engine will not restart and will quickly stop (truly choke!) due to an overly rich mixture. * A defective carburetor may also cause the mixture to be too rich or too lean.
All common lawn mower engines require a precisely timed spark to ignite the air-fuel mixture in the cylinder. The existence of a spark can easily be tested as follows: WARNING: make sure there is no gas in the vicinity when performing the following test! Remove the spark plug wire and insert the blade tip of an appropriately sized and well insulated (plastic) screwdriver inside the boot or clip in place of the spark plug. While holding the *insulated* part of the screwdriver, position the metal part of the blade about 1/8th inch from the block or frame. An alternative technique is to use an old, but good, spark plug whose gap has been increased to about 1/8 inch or one specially made for exactly this purpose. In this case, simply connect the spark plug wire to the test plug and hold its threaded part against the cylinder head or other part of the chassis (away from the gas tank!!). Note: Just positioning the spark plug wire a short distance from the spark plug terminal is not recommended as the results of this test will then depend on the condition of the spark plug as well since the spark will have to jump two gaps. Have a buddy crank the engine at normal starting speed so that you will be able to hold the screwdriver or test plug steady and be close enough to see any spark clearly. Shield the gap from the sun or bright light if necessary. You should see a nice healthy spark jump the gap several times on each pull (actually, once per rotation of the crankshaft/blade on both 2 and 4 stroke engines). Note: 4 stroke engines ignite the air-fuel mixture on every other rotation of the crankshaft. The extra sparks fire harmlessly into the exhaust gasses and are wasted. Can you believe it?! CAUTION: if you are not well enough insulated, *you* will jump several times per rotation of the crankshaft/blade if the ignition system is functioning properly! Hey, that *is* a valid test! If this test confirms the spark, it is still possible that the spark plug is fouled or bad. See the section: "Checking the spark plug". If there is no spark, then there is a problem with your ignition system.
If your mower is less than 15 years old, there is an excellent chance that
if uses an electronic ignition system. These are very reliable as there
are no points or condenser to go bad and no need for routine tune-ups.
However, a number of other problems can result in lack of spark:
Make sure stop switch/stop wire is in appropriate position - confirm with a
multimeter, check that flywheel is being spun by starter and that flywheel key
is intact to assure proper timing, check condition of points/condenser and
setting (if applicable), test magnet (on flywheel) for strength, check the gap
between flywheel and magneto core. If these are all fine, test or replace
the magneto.
In more detail:
1. Check for a faulty or misadjusted STOP switch. This may be activated
by releasing the dead-man bar or by a throttle control lever (STOP, RUN,
START). Inspect the cable, linkage, and wiring for damage or for
something that may have come loose.
2. Check that your starter is actually spinning the flywheel. If the
flywheel is not rotating properly when you pull the cord or turn the
electric start key, then there is a problem with the starter, not the
ignition system. Or, the flywheel is not tight due to a sheared flywheel
key or improperly torqued flywheel nut.
3. Check for a flywheel that is loose and not seating properly on the taper.
This could result in no spark if the air gap between the flywheel magnet
and magneto core is then incorrect. However, due to the close spacing,
you would probably feel and hear serious scraping in this case.
Items (2) and (3) are likely if your just attempted to move a curb with
your mower blade (or if someone inadequately tightened the flywheel nut
during some previous maintenance).
4. Check for bad connections or defective wiring including faulty or
water logged insulation. If you just gave the mower a shower, wait
ample time for it to dry out. High humidity may result in more
problems if the insulation is not in good condition as well.
5. Check for a weak (or missing) flywheel magnet. Both of these faults
are extremely unlikely unless you have been hammering and whacking the
crankshaft and flywheel in an effort to remove the flywheel. (This is
not recommended - see the section: "Flywheel removal".)
6a. Electronic ignition - There is likely a single potted module which includes
the circuitry and ignition coil. If anything goes wrong with this module,
replacement is the only option. Once the wiring and resistance of the
secondary has been checked, there are really no addition tests that can be
performed on an electronic ignition module without special equipment. A
defective ignition module will have to be replaced.
6b. Breaker point ignition - Possibilities are bad, dirty, corroded, or loose
points or points that are grossly out of adjustment, a bad condenser, or a
bad magneto coil. See the section: "Maintenance of point-type ignition systems".
See the section: "Testing the magneto".
First, check that the dead-man bar is properly disengaging the stop switch
when pulled and/or throttle control is properly disengaging the stop switch
when in the start or run position.
For anything beyond this, disassembly will be needed to identify and replace
any defective parts.
If the no-spark condition happened after after the blade hit an obstruction,
(1) or (2) are likely. See the section: "Lawn mower will not start after the blade hit an obstruction".
Use the proper socket to remove the spark plug and inspect it for damage and general appearance: * Light gray or brown and smooth - this is the normal appearance. The mixture is correct and there likely no major problems with the engine. * Excessive black carbon - the mixture may be too rich or the spark plug may be the wrong type for your engine. * Damage to the electrodes - the mixture may be too lean, timing may be set incorrectly, or the spark plug may be the wrong type for your engine. The best thing to do at this point is just replace it with a new spark plug and worry about the old one later. Actually, nearly every small engine maintenance book will recommend changing the spark plug every season anyhow.
The magneto, like the ignition coil on an automobile, contains two windings: * A primary with a few turns of heavy wire. * A high voltage secondary with thousands of turns of super fine wire. In an automobile, the battery supplies the primary current; in a magneto, the magnet on the flywheel moving past the core at high speed acts as a generator and induces current in the primary. As the magnets spin past the pole pieces of the magneto core, the points are closed and current builds up in the low voltage winding (and flux builds up in the core). At or slightly before Top Dead Center (TDC), the current (and flux) should be maximum and at this instant the points open. The flux then collapses (and the condensor (capacitor) across the points acts as a snubber allowing the current to bypass the open points and preventing arcing at the point contacts). This rapid decrease in flux results in coupling of the stored energy to the turn high voltage winding and results in up to 10,000 V or more at the spark plug. (For EE types, this is somewhat similar in basic operation to the flyback converter in a switchmode power supply except that the moving magnet supplies the input power instead of the rectified AC line and the points act as the switch instead of a power transistor.) The secondary will always be accessible for testing but the primary of an electronic ignition may be not be due to the electronic components: * Secondary: 3 K ohms (maybe a little higher but not open). Much lower would indicate a shorted winding. * Primary (if non-electronic and accessible): very low - guessing less than an ohm. Wires can break due to corrosion or vibration. This would result in an open winding - infinite resistance. Shorts can develop between adjacent windings or to the core. This may be detectable as reduced resistance but without knowing exactly what it should be, there is no way of knowing if a slight discrepency represents a problem or just slight variations in design or manufacturing. A more complete test would involve checking the 'Q' or doing what is called a 'ring' test and even more for an electronic ignition. This requires special equipment. Therefore, it is best to swap in a known good unit. They are not that expensive.
For power to be developed, the ignition of the compressed air/fuel mixture must take place at exactly the correct instant - just before the piston reaches Top Dead Center (TDC) on the compression stroke. With automotive engines, there are mechanisms to advance the spark at higher revs but simple lawn mower engines do not have this complication, at least. Timing is set on older mowers with point type ignition systems by adjusting the point gap and generally only changes due to wear. However, these changes are gradual and unless the points come loose for some reason, will not likely suddenly prevent the mower from starting. On newer electronic ignition systems, there is basically no adjustment as the position of the electronic ignition coil/module fully determines ignition timing and this is fixed. However, timing can be grossly messed up if the flywheel key gets sheared and the flywheel then rotates a fraction of a turn on its mount on the crankshaft. This is very likely to happen should the blade strike a rigid object causing the mower to stop instantly. In this case one or both of the blade lock key and flywheel key have sheared to (hopefully) protect the very expensive internal parts from damage. There are likely not going to be any timing marks for that old timing light you have sitting gathering dust somewhere. The only test really is to inspect the flywheel keyway to determine if damage has occurred. See the section: "Lawn mower will not start after the blade hit an obstruction" as this is the most likely cause of a sheared flywheel key.
The following description applies to most small rotary lawn mowers with direct driven blades. The vast majority of these use either Tecumseh (as found a variety of Sears/Craftsman equipment) or Briggs & Stratton engines. However, similar comments apply to others as well including Lawnboy two stroke engines and the more modern Honda and other overhead valve type of engines. The assumption is that the engine started and ran normally prior to the incident. Now, no matter how many times you yank the starter rope or run the electric starter, it will not start at all, bucks, kicks back, backfires, or fails to develop enough power to keep going on its own. If the blade struck a solid boulder while the engine was set on 'high', more severe damage is possible as even with soft metal keys locking the blade and flywheel to the crankshaft, the inertia of the rotating blade is acting sideways against the crankshaft in addition to suddenly stopping its rotation. This can result in a bent crankshaft. The end of the crankshaft with the blade adapter could be bent without affecting the bearings or internal parts. This would need to be tested for as well. Not that such an occurrence is that much better - the crankshaft would still have to be replaced but at least the bearings in the crankcase will not be damaged. If the starter will not turn the crankshaft (assuming you remembered in your haste to engage the safety bar) - it is seized or will only rotate part of a revolution before hitting against something solid inside - then you probably have serious internal damage that will require a complete strip down and replacement of some (expensive) parts. If it turns but much more tightly than you recall (assuming you do have the safety bar engaged!) then the crankshaft may be bent - again very expensive. Repair may not be worth it. However, in most cases, what has happened is that either or both of the blade lock key and/or flywheel key have sheared to protect the crankshaft from serious (and terminal) damage. If the blade lock key broke, the blade will no longer turn rigidly with the crankshaft and provide the inertia required by many small engines with undersized flywheels. If the flywheel key broke, the ignition timing will likely be totally wrong and the result may be no ignition, backfiring, kickback, or weak or total loss of power. To diagnose, proceed as follows: First, pull off the spark plug wire and tie it securely away from the spark plug terminal (several inches minimum) or remove the spark plug entirely so that there is no chance of the engine accidentally starting. Even though it will not start now no matter what you do, the underlying problem could actually be a flooded carburetor or something else which may correct itself while you are working. Never take chances. Drain the gas or remove the fuel tank. This will prevent gasoline from spilling out the gas cap vent hole or flooding the engine through the carburetor since you will need to tip the mower to get underneath. Set the mower on its side (carburetor side up). CAUTION: Immediately check for oil leaks at the oil filler pipe or elsewhere. The mower can usually be set on its side for a few minutes without harm but if these occur - you will have to work with it tipped less than 45 degrees or so - propped on wood blocks. Or, use this as a good excuse to perform an oil change and drain the oil (even if the engine is cold, most of the oil will drain out - it will just take a little longer). Just don't forget to refill the crankcase with fresh oil once you have completed your work! Using an old rag and/or proper work gloves, grasp the blade and attempt to rotate the blade and crankshaft. CAUTION, despite your lack of maintenance, the blade may be sharp!). The blade and crankshaft should rotate together. If there is slippage, the key has broken and will require replacement of just the key or the entire blade adapter plate depending on design. If it appears to be intact, then you can assume the flywheel key has broken. The blade key may be broken as well but it is not likely the reason for your failure to start. You should remove the blade to determine this for sure before restoring the mower to service in any case. See the section: "Non-violent blade removal". To inspect the flywheel key, some disassembly is required.
Remove the shroud (blower cover) if you have not done so already. This is
usually fastened with 4 screws and hopefully does not involve any head
bolts - if so, you will need to tighten them to the proper torque using a
torque wrench once you have remedied the problem. You may need to remove
the fuel tank (if you have not done this already) and other trim pieces as
well.
You should now see the top of the flywheel. In most cases, a large nut
fastens the flywheel to the crankshaft. (However, in some designs, part
of the starter mechanism is actually used and this is supposed to require
a special wrench to remove. However, using a piece of wood as a buffer
and tapping the ears in a counterclockwise direction will work also. Refer
to your engine manual for details.) Use the proper socket to loosen this
nut (counterclockwise). It may be necessary to brace the flywheel securely
to gain enough leverage. Make sure this is done against something that can
stand the force. Once loose, remove it by hand and then remove any washers
or other parts that are under it. Make a note of how these were positioned
including which side is up on some cupped washers.
You should now see the keyway. The slots on the crankshaft and flywheel
should be aligned. There are two common types of keys:
* A rectangular or D shaped piece of soft metal that locks the flywheel
and shaft. You should be able to see if the two identically sized slots
are still aligned.
* A piece of soft metal with an L-shaped cross section. The slot on the
crankshaft is narrower than the slot on the flywheel and is slightly offset
(thus, the L). Again, it should be obvious if the two slots are still
aligned.
You may even find that the flywheel is relatively loose on the crankshaft
if rotating the blade while holding the flywheel stationary is possible.
Either the blade key or the flywheel key or both are broken in this case.
You will have to remove the flywheel to replace the key if it is broken or
damaged.
If the flywheel is loose at this point, then the following will not be
needed as it can be lifted off.
There are several approaches to flywheel removal:
* The best way by far is to use a special puller designed for your particular
engine. Briggs & Stratton and Tecumseh flywheels usually have 2 or 3 holes
placed around the center of the flywheel which are used with special puller
blocks. These have self tapping bolts which you thread into the holes and
then tighten down nuts to pop the flywheel off of the crankshaft. I have
made my own blocks for this purpose from scrap steel. If you have a drill
press, it is not difficult. Alternatively, you can purchase these from the
engine manufacturer. The use of a puller really does reduce the use of 4
letter expletives and virtually eliminates the chance of damage to the
flywheel or crankshaft by the alternative techniques.
___ ___
|___| |___|<-------- Self tapping bolts or pretap holes.
| | | |
_|-|_ _|-|_
| |-| | | |-| |<------- Tighten nuts to release flywheel.
___|_|-|_|__________|_|-|_|___
| |-| |-| |<--- Plate or block - 1/4" or thicker steel
|_____|-|______________|-|_____|
|-| .-.----.-. |-|
|-| | :----: |<-|-|---------- Flywheel nut - loosen slightly.
|-| |_:----:_| |-|
______|-|___ :----: ___|-|______
//////:-:///|:----:|///:-://////
//////:-:///|:----:|///:-:////// <-- Flywheel comes with predrilled holes.
//////'-'///|:----:|///'-'////// (taper not shown - ASCII limitations!)
//////| |///|:----:|///| |//////
Bolts are screwed into holes in flywheel. Then, plate bears against the
flywheel nut (slightly loosened) and the nuts are tightened alternately
until the flywheel pops off.
WARNING: do not use an ordinary gear, clutch, pulley, bearing, or other
puller unless this is specifically mentioned as a recommended technique
in your engine manual. The flywheel could be damaged - possibly not
immediately obvious - but the result could be catastrophic failure once
the engine is put back into service.
* A 'knock-off tool' is a special closed-end nut that you thread onto the
crankshaft in place of the normal flywheel nut. You then are supposed to
pry under the flywheel with a pair of large screwdrivers while tapping
the knock-off tool with a soft hammer. Aside from the fact that as
described, this requires 3 hands, this may or may not work easily.
Depending on conditions, the flywheel may pop off at the first tap or
may stubbornly refuse to budge no matter how much you whack. If not done
properly, it is possible to bend the crankshaft - very expensive. Some
people also worry that the shock will damage internal parts or even
partially demagnetize the magnet on the flywheel. Thus, my preference
for the puller unless the first couple of taps releases the flywheel.
* Many engine books will simply recommend threading the flywheel nut back
on flush with the end of the shaft and tapping this with a hammer as
above (with the 3 hands). The risk here is that the threads may be
damaged in addition to the possibility of bending the shaft or causing
other damage. Use a piece of soft metal - aluminum, brass, or lead - to
protect the end of the shaft and nut. In any case, only use this approach
as a last resort.
Once the flywheel is off, inspect the keyway on the crankshaft and flywheel for damage. Serious damage will require replacement of the affected parts. Slight burrs can be removed with a small file. If there are any cracks in the flywheel radiating from the hole, the flywheel MUST be replaced as this is a serious safety risk - the flywheel could literally explode when run at full speed. However, don't be concerned by surface flash - lines that look like fine cracks resulting from the molding process. To confirm that these are not cracks, there will be no visible penetration inside the shaft hole and fine sanding will quickly remove all traces of this flash. Assuming there is no serious damage, a new flywheel key should be all you need - about 25 or 30 cents. To confirm that this is all you need, replace the flywheel without the key but line up the two slots as they would be if a key were present. Tighten securely (but it doesn't need to be to the full torque as this is just a test). This should permit the mower to start and run normally but I would not recommend using the mower to actually cut grass until you replace the flywheel key. To install the new one, insert the key into the slot in the flywheel first and then slip the entire affair onto the crankshaft (I like to use a bit of WD40 for protection as well). The flywheel should seat securely with no detectable free play - it should be on straight and not rock back and forth at all. If this is not the case, the key may be in upside-down or there may be something or some particles of dirt or metal blocking it. Replace the washers, dirt screen, etc., and then hand thread the flywheel nut as far as it will go. Tighten to the specified torque (typically, 30-33 ft-lbs). Note: There may be a cupped washer between the nut/screen and flywheel. This must be installed cupped-side facing the flywheel or else you will be probably be replacing the flywheel key again very soon :-(. WARNING: Do not install a hard steel key in place of the recommended flywheel key as you will lose the protection that the soft metal provides and the next incident may be the last... See the section: "Why soft metal keys must be used". Then, replace the shroud, fuel tank, etc. If head bolts had to be removed, it is probably a good idea to slightly loosen all of the head bolts and then retorque them to the proper value in the recommended sequence for your engine.
Normally, the soft metal keys lock the blade and flywheel to the crankshaft. However, should the blade strike an obstacle and stop suddenly, one or both key(s) will shear and reduce the likelihood that the very expensive crankshaft or other parts will be damaged. The reason is that the substantial inertia of the crankshaft and that of the flywheel will tend to try to keep them rotating. Something has to give and you want it to be the 25 cent key and not the $75 crankshaft! However, this isn't foolproof as explained in the section: "Why you really don't want to attempt to move an immovable object".
For the most part, smoking is just as bad for a small engine as it is for
you. Excessive smoke from the engine may be an indication of of problems
with the carburetor, rings, or gasoline:
- Black smoke is a symptom of an overly rich fuel-air mixture. This could
be caused by a choke that is partially closed, a faulty carburetor, or
the need for a carburetor adjustment. Make sure the choke if fully open.
See the sections on carburetor adjustment and carburetor cleaning.
- White or black smoke may also result from yard debris, oil, or other
contaminants on the exterior of the cylinder as the temperature after
a few minutes of operation will reach several hundred degrees F even
with proper cooling. Stop the engine and let it cool for a few minutes.
Then, check around the cylinder, cylinder head, and under the shroud for
grass clippings, leaves, oil or other spills, dead rodents, etc.
* 2 stroke engines will always produce some fine white/blue smoke since
the lubricating oil in the fuel mixture is being burnt along with the
gasoline.
- Excessive white/blue smoke could indicate an incorrect ratio of gasoline
to oil or a mixture which has been sitting around for a while - the more
volatile gasoline evaporates leaving behind the oil. It could also be
an indication of contaminated fuel.
* 4 stroke engines should produce virtually no smoke while running. At
first startup of the season, there may be a few seconds of white/blue
smoke resulting from the oil squirted into the cylinder at the end of
last season (you did the preventive maintenance, right?) burning off
as well as white smoke/steam from accumulated moisture. If you tip the
mower on its side routinely (to clean out grass clippings, for example), oil
may seep into the cylinder resulting in white/blue smoke at startup as well.
- White or blue smoke while running may be an indication of an excessively
worn cylinder or rings or a clogged or inoperative breather. Or, you may
be using the fuel mixture for your 2 stroke weed whacker by mistake!
While some may describe the engine of an antique automobile as 'purring', this will not likely apply to most gasoline powered lawn mowers. It would seem that noise reduction is just not a high priority design issue with lawn mower engineers or marketing types. However, even if not exactly quiet, the sound made by a healthy mower should not be similar to that of a pig being tortured. * A screeching or squealing sound may be the result of worn bearings or inadequate lubrication. This could be due to lack of oil (!!) or a problem with the oil distribution system (pump, passages, slinger, etc.). It could also be a problem with auxiliary mechanical parts - power take-off, front wheel drive, or a starter clutch that fails to disengage. * Banging or rattling noises may be due to parts that have worked loose due to vibration or by being inadequately tightened (by someone else, of course). The entire engine may be bouncing around on its mount. Or, the flywheel, blade, attachments, or chassis parts may be vibrating. Even if everything appears secure, there is quite a bit of energy associated with an engine running full throttle and parts can work loose. * A low frequency shuddering or vibration may be due to debris under the deck. Check for wads of matted grass, twigs, branches, and 3 foot logs, caught in the baffles or exit chute. Sometimes, globs of this stuff fall off and get slung by the blades with all sorts of associated strange sounds. A combination of the above are also possible. For example, a loose flywheel could result in it scraping against the magneto yielding a sound like a cat being squeezed to death (or that of a first year violin student) but possibly only at high revs :-). Of course, a badly worn engine can also result in piston and rod slap and other mechanical noises as internal parts with excessive clearances whack one another. A complete engine overhaul may be in order or just tolerate it and plan for a new mower when the final day arrives (or your neighbors take up a collection).
Wheels tend to get banged about and damaged or may just become loose and unstable due to wear. Wheels and wheel bolts are readily available at home centers (or Sears for Craftsman mowers). * If really frozen, the use of penetrating oil like WD40 or Liquid Wrench should permit the old bolts to be removed using one or two wrenches (sockets preferred). * In some cases, adding some metal washers on the axle may help to reduce wobble on a worn wheel which is too loose. * The best type use ball bearings and will outlast the mower but I wouldn't expect to see this on anything less than the gold-plated model! However, ball bearing wheels can be installed as replacements. * Use of WD40 can help to ease the pain of switching the cutting height of lever operated wheels.
Simple float carburetors are found on a variety of equipment including many engines made for Sears by Tecumseh. The basic procedures applies to the float carburetors of other manufacturers as well. If you have been following the recommended preventive maintenance procedures, this may never be needed. But, face it, you do not! The most important PM that is not likely done by 90 percent of mower owners is to drain the gas at the end of the season. With float type carburetors in particular, the result is a buildup which eventually clogs the very fine passageways in the carburetor. What happens is that the gas in the carburetor bowl gradually evaporates leaving behind the gunk and varnish. New gas then flows in from the fuel tank which then evaporates leaving behind more gunk and varnish, and so on and so on and so on. This eventually, well, gums up the works by interfering with float movement and clogging the precision metering holes. Thus, the need for cleaning. Symptoms include difficulty in starting, flooding, surging, lack of power, difficulty in restarting when hot, etc. The following procedures are specifically for the common non-adjustable carburetors used on the vast majority of Craftsman mowers manufactured in the last 10 years. Carburetors with adjustments and/or a choke are slightly more complex and may differ in other ways. Refer to a small engine repair book or your engine manual for further information. Carburetor removal: * Drain the fuel, close the shutoff valve if any, or remove the gas tank. On the common Craftsman mowers, the tank either slips off or is fastened with a couple of screws. The gas line should pull right off. Inspect the fuel line for damage or cracking and replace it if these are severe. * Remove the air filter, inspect, and set aside. The small plastic enclosed air filters twist off counterclockwise. If it is clogged and of the paper type, replacement will be needed. If it has a foam element, this can be reused if it doesn't fall apart. Remove the foam element, clean in soap or detergent and water, dry, and then coat it with a few drops of fresh engine oil. Work the foam with your fingers to distribute the oil. For other types, see your engine manual. * Use a large philips screwdriver to loosen the two screws fastening the intake manifold to the cylinder block. If the gasket separates easily and cleanly, then it can be reused though a dab of non-hardening sealer is advisable once you have tested the mower to be sure that your newly restored carburetor is functioning properly. If it tears or is damaged in any way, then it should be replaced. If the bolts are really tight, an open end wrench may be of help but common sockets may not fit around the bottom bolt. Thin walled sockets may work. * Disconnect the throttle linkage and governor spring noting which holes they go in. IMPORTANT: If you get this screwed up you could have a runaway situation on your hands when you go to restart it. This can destroy the engine in a few seconds! * Disconnect the rubber tube from the primer bulb, if any. It should pull off. If it tears near the end, there is probably enough slack so that a new tube is not required. * Disconnect the speed control and stop switch wire, if any. Note how they are installed. The carburetor can now be moved to the convenience of your workbench. WARNING: there is still likely a significant amount of gas inside the float bowl. Initial disassembly at least should be done outside so that you can dispose of this safely. Working outside is advisable in any case as the common carburetor cleaning solvents are both flammable and bad for your health.
Most carburetors on Craftsman mowers are variations on a common float design. Newer mowers tend to have no adjustments and no choke - which greatly simplifies cleaning and adjustment. With respect to adjustment, there is none - it either works or it doesn't. If it doesn't, your cleaning was not thorough enough, some parts need replacement, or the problem is not in the carburetor. * Under the bowl is a large hex head bolt. On the non-adjustable carburetor, this is closed on the bottom. It is also not a simple bolt but includes the precision main fuel metering hole which will need to be cleaned thoroughly. Use a proper socket to unscrew this bolt (counterclockwise). Drain any residual gas from the bowl. * There is a fiber washer under the bolt. There may also be a fiber washer on this nut inside the float bowl. Don't lose these or get them mixed up. Turn the carburetor upside-down. * Carefully remove the bowl and O-ring. Inspect these for damage. (Note: there is probably a dimple in the bottom of the bowl in the lower level side. This is normal and probably there to keep the float off of the bottom where gunk and varnish collect because you didn't drain the gas.) * The float will now be visible. Rotate it to the fully up position. The inlet needle will come up with the hinged part of the float. It is held in place by a wire clip but will now be free. The inlet needle is actually a four sided metal rod with a polished conical tip. Remove the needle and clip. * Use a pair of needlenose pliers to pull out the hinge pin which will free the float. Careful - the float is made of relatively thin brass and is susceptible to damage. Check the throttle plate for free movement - there should be absolutely no hint of binding or tightness. If there is, then this will need to be disassembled as well and cleaned: * Use an open-end wrench to loosen the intake pipe and then remove the nuts and bolts. The manifold will probably come free with the gasket intact. Don't lose the metal strip to which the governor spring attaches. Check for dirt and other debris and set aside. * Use a 1/8" straight blade screwdriver to remove the screw in the center of the throttle plate. Note the position of the hole in the plate and the orientation of the plate. (The hole should be toward the engine side with the carburetor body upright. Mark it before removal if in doubt.) * Tap the carburetor if needed to remove the throttle plate. * Pull the throttle shaft out of the carburetor body. Take care not to lose the spring with the felt and/or metal washer. Note their positions.
Use carburetor cleaner and lint free cloths or paper towels to remove all
built up brown or green gunk, varnish, and other contamination from the
metallic parts. Pay particular attention to the machined passages and
metering holes.
Take care where non-metallic parts are still in place as extended contact
with harsh solvents may degrade their properties (inlet seat and primer
bulb, if present). Low pressure compressed air may be used to blow out
passages but only use this on the fuel line from inside the carburetor
body - else you may end up with the inlet seat clear across the driveway
never to be found again.
DO NOT use wires or metal instruments to clear any of the passages and their
size is critical.
The small hole in the hollow bolt on the bottom is most critical. Make
sure it is cleaned down to the shiny brass and that this hole is unblocked
and fully open:
_ _
| | | |
| | | |
| | |_|
| | _ Hole in nut (approximately .025") - use carburetor cleaner
| | | | and wooden toothpicks to clear it out down to shiny brass.
| | | | DO NOT use metal wires!
_| | _ | |_
| \_/ |
|___________|
I first use carburetor cleaner inside and out with cotton swabs to remove
all traces of gunk from the inside. Use as many as needed till no more
discoloration shows up. Then, use the broken end of a wooden toothpick or
popsicle stick to clear the .5 mm diameter hole in the side. In severe cases,
this hole may not even be immediately visible due to the varnish and gunk
buildup.
If this hole is norrowed or clogged, the engine may start but then die in a
few seconds. Gas enters the reservoir in the nut slowly or is forced in by
priming but the normal suction cannot replenish it quicly enough.
Fine steel wool may be used on the float hinge pin if it is rough or there
is evidence of rust but do not use anything abrasive on any of the other
parts. Persistence with carburetor cleaner and cloths or paper towels
should prove sufficient.
Inspect the inlet needle and seat. The needle should have sharp uniform
edges and no visible damage to the conical tip. Any damage half way down
the conical part - where it actually contacts the seat - will result in
leakage and flooding. The seat can be removed if damaged by pulling it
out with a hooked wire - careful - you do not want to scratch the body!
If removed, do not reuse but install a replacement. The new seat goes in
groove side first (lubricate with a drop of oil) and can be pressed home
with a blunt rod.
If the throttle plate was disassembled, clean these parts with carburetor
cleaner use a cotton swab to get into the bearing surfaces in the carburetor
body.
DO NOT attempt to disassemble the carburetor beyond this point - the pressed
in main fuel nozzle is precisely fitted and is not removable. The welch
plug (pressed in disk) should not be removed unless you suspect contamination
in the primer chamber (if any).
Carburetor rebuild kits are available and are economical where almost any
parts need replacement.
* The inlet needle and seat must be in good condition or else the carburetor will flood due to leakage or result in erratic operation due to uneven gas flow. If there is any evidence of damage, these parts will need replacement. The 4 edges of the needle should not be worn (the sharpness would change about 2/3 of the way from the pointed end). If the edges are noticeable rounded, replace the needle. * The float height adjustment should be fairly accurate. With the float and inlet needle reinstalled (and the seat replaced if it was removed), invert the carburetor - the float should sit just about horizontal. For more precision, a .210" (#4) drill bit should just fit between the body and the non-hinge end of the float. * The machined passages must be free and clear and not damaged - never use wires to clean them. Use compressed air, carburetor cleaner, wooden sticks, etc. However, do make sure that they are fully open. There are no blind passages in these carburetors so a strong light should permit you to see that they are unblocked (the following are typical - your model may differ slightly): - Air bleed, inlet side angled down toward main jet. - Passage to primer chamber, inlet side. - Slot towards center at edge of welch plug (may not be present). - Pair of main fuel passages in central cylinder in main body. - Main metering hole in bowl bolt. * The hole in the bowl bolt is the main metering orifice and it is critical to the proper operation of the carburetor. This area also tends to collect a lot of crud. It will yield to repeated use of carburetor cleaner, cotton swabs (Q-tips), and wooden sticks. Continue cleaning until you are down to shiny brass. Just don't become impatient and use any wires or sharp tools to speed the process! * If the primer bulb is on the carburetor, there is a 'welch plug' (a metal disk pressed into a mating cavity) sealing the primer chamber. On the side toward the center, there is a tiny rectangular hole that must be open - it often gets clogged and may not even be readily apparent. Do not attempt to remove the welch plug unless you suspect something is inside. * The float must be air (and gas) tight. Shake it - if there is anything inside, the float will need replacement. Put it under water - there should be absolutely no evidence of bubbles and leakage. Pinholes sometimes develop in the thin brass and while these can be soldered, this practice is not recommended. * The large O-ring must seal properly. If it leaks, the engine will run rich and contaminants may enter the carburetor bowl. Replacement is usually recommended whenever the carburetor is disassembled. However, if it is in perfect condition, you can try to reuse making sure that the mating surfaces are clean and smooth. Use some engine oil on the O-ring to assure a tight seal.
Once all parts have been cleaned and inspected - replaced where needed, proceed as follows: If you removed the throttle assembly: * Reinstall the throttle shaft along with its spring and felt and/or metal washer. Hook the spring onto the ridge on the carburetor body. Make sure it moves freely. DO NOT lubricate. * Attach the throttle plate to the shaft with the original screw. Make sure the plate is correct side out and that the hole is positioned on the right facing the upright carburetor from the throttle plate side. As you tighten the screw, slightly rotate the throttle shaft to allow the plate to seat properly - jiggle it a bit at the same time. When properly installed, the plate itself limits the return movement of the throttle. It should be fully closed at this point. Confirm that the throttle plate moves freely between a fully closed and fully open position - there should be no hint of binding or stiffness. * Reattach the air inlet pipe with gasket using the two sets of nuts and bolts. Don't forget the metal strip for the governor spring if your carburetor uses this. Tighten securely - 4 to 6 ft-lbs if you use a torque wrench. Now for the main event: * Install a new seat if you removed the old one. The new seat goes in groove side first (lubricate with a drop of oil) and can be pressed home with a blunt rod. * Install the float using the hinge pin. * Insert the inlet needle hooking the retaining clip on the tab near the float hinge. Check for free movement of the float. * With the carburetor body inverted, check the float height adjustment. It should seat almost horizontally. For a more precise test, use a .210" (#4) drill bit as a gauge across the outer ring of the carburetor body - the float should just touch this. Bend the tab on the float to adjust. (Note: unless you replaced some parts, this setting will probably be fine.) You can test for proper operation using low pressure compressed air (i.e., by blowing into the fuel hose), or water or gas. Water is safest but you must make sure to dry everything thoroughly before final assembly. To do this, temporarily reassemble the bowl with the hex head bolt. With the carburetor upright, dribble water into the fuel hose until it accepts no more - perhaps an ounce or two. There should be no leakage - the level of water in the hose should not change at all once it stops. If there is any leakage, there is still a problem with the inlet needle or seat - or the float is gas-logged. * Install the large O-ring around the carburetor body. Use a small amount of engine oil to aid in assuring a good seal. * Place the bowl over this assembly making sure that it does not pinch the O-ring. Orient it so that the deep part is almost opposite the float hinge (it should actually point directly away from the engine when the carburetor is mounted.) * Install the hex head bowl bolt and fiber washer. Tighten securely (but there is apparently no recommended torque for this bolt).
With the carburetor positioned in its approximate location on the engine: * Reinstall the throttle and governor linkages Where there is no speed adjustment or idle position, the direct governor linkage goes in the hole closest to the engine and the spring hooks onto a fixed vertical metal strip with only one hole at one end and the lower hole in the governor lever at the other. Thus, in operation, the spring attempts to keep the throttle open and the governor pulls on the throttle to close it. Increased spring tension results in higher speed. Don't get these backwards when you go to reinstall the carburetor on the engine!!! * Reattach the primer tube, if any. * Reattach the stop switch wire, if any. * Install the carburetor onto the engine with a new gasket if needed. Tighten securely (6 to 8 ft-lbs). * Double-check that the throttle linkage and governor spring are in the proper holes and nothing is binding - you should be able to move the throttle back and forth without any sticking or tightness. It should return to the full counterclockwise position instantly as a result of the governor spring tension. * Do not replace the air filter at this time. * Reinstall any throttle selector or cable. Confirm that it operates properly - usually STOP, LOW, HIGH. STOP should engage the stop switch. LOW should leave the governor spring tension where it was. HIGH should increase the governor spring tension slightly. If there is an IDLE position, the throttle plate should be almost closed. * Reinstall any trim pieces that were removed. * Reinstall the fuel tank and fuel hose with clamp, if any. Open the fuel valve, if any.
Add a small amount of gas to the fuel tank - perhaps half a glass or so. Just enough to assure that it will reach the carburetor even if the mower is slightly tilted or jostled. Inspect around the fuel hose and carburetor body for fuel leaks. If gas starts dripping from the air inlet or anywhere else, there is still a problem with the inlet needle and seat. Disassembly will be required. Only a few seconds are needed for the gas to fill the carburetor bowl. Assuming there are no leaks, install the air filter and reattach the spark plug wire or reinstall the spark plug. Attempt the normal starting procedure - prime if recommended. The engine should start on the first pull! Immediately move the throttle selector to LOW if you have this option. Confirm immediately that it stabilizes at a reasonable speed - stop it quickly if it sounds like the mower is preparing for takeoff - your governor connections are incorrect or binding. If it runs at a fast speed with the speed selector set at LOW, the governor spring is probably in the wrong hole. Check it. Listen and feel for any significant unevenless, surging, or other unusual behavior. Stop the mower, wait a few seconds, and restart. It should restart with a single pull without priming. Mow for a few minutes. Stop the engine and confirm that it restarts without priming. Listen and feel for any indication of lack of power or other unusual behavior. Go take a dinner break. Then confirm that the engine will now start - priming may be needed since it will now be cold.
In most cases, missing or total lack of spark will be due to dirt, pitting, or corrosion of the points or a failure of the condenser. Timing may affected as well by excessive wear. The following procedures should restore the ignition system to good health: First, test for spark. If there is a spark, try replacing the spark plug since this is the most likely cause of ignition problems. With a spark present, there could still be ignition system problems but this is much less likely. You may be able to test the points to some extent if you can get to the wire that connects to the magneto or the STOP switch. A multimeter on the low ohms scale will the permit you to watch the opening and closing of the points. If this confirms that the points are operating the condenser could still be defective, the breaker arm could be sluggish, or the point gap could be grossly out of adjustment. To proceed further: * Remove any trim pieces and the shroud/blower housing to access the flywheel, magneto, and points assembly under the flywheel. * Check the flywheel magnet to magneto core air gap. While it is extremely unlikely that this increased, it is an easy test. The correct value is usually .015 inches but some engines use other gap spacings. A non-magnetic feeler gauge is best for this. If it is much larger than specified, adjust it and test for spark again. * Remove the flywheel. See the section: "Flywheel removal". * Test the flywheel magnet. No actual strength is usually published but if it attracts a steel screwdriver from at least a 1/2" distance and seems strong, the magnet is likely fine. If it is weak (or missing, though this is mostly a theoretical possibility!), the flywheel will need to be replaced. * Remove the cover over the breaker points assembly, if any. * Inspect the points. There should be no serious pitting, corrosion, evidence of arcing or sparking. Nor should they be welded together! If any of these problems are present, replace the points and condenser as well - a bad condenser may be the cause of the points failure it is not really possible to fully test it. You can also test for electrical operation of the points using a multimeter on the low ohms scale while rotating the crankshaft (you will have to use the blade - careful) or operating the breaker arm manually. Or better yet, just replace the points and condenser. The cost is minimal (probably under $5 for a rebuild kit) and you have already done most of the work. * Note the mounting arrangement and remove the old points and condenser and install the replacements. Do not tighten the locking screws at this time.
Perform the following whenever the breaker points assembly is replaced or
where a timing problem is suspected.
* Rotate the crankshaft so that the cam that operates the points is at the
highest location and the points are wide open.
* Adjust the point gap setting to specifications using a feeler gauge. This
is nearly always .020 inches.
* Set the crankshaft position. This is usually done statically and does not
require a timing light (Darn!).
- On many engines including Tecumsehs, there is a timing dimension in the
engine specifications. This is the distance of the piston below Top Dead
Center (TDC) at which the points should just open.
While measuring piston position with a scale through the spark plug hole,
rotate the crankshaft until the piston is precisely at TDC and note this
distance. (There are special timing gauges for this prupose with lock
screws to hold the setting but a little ruler will work just fine.)
Now, turn the crankshaft in the opposite direction from normal rotation
(usually counterclockwise as viewed from the flywheel end) until the
piston moves down .25 inches or so and then turn it slowly in the normal
direction of rotation until the piston position is precisely at the timing
dimension listed in your engine specifications.
- On some engines there will be timing marks on the flywheel and engine
block or the manual may tell you to line up the one edge of the flywheel
magnet with one of the magneto pole pieces.
The flywheel should be temporarily re-installed without tightening the nut.
Rotate the crankshaft until the timing marks are precisely aligned.
Carefully remove the flywheel without disturbing the crankshaft position.
* Adjust the timing. Loosen the locking screw on the points assembly.
Rotate the points assembly until the points just open (use a thin piece
of cellophane or a multimeter on the low ohms scale. Lock the position
by tightening the set screw.
* Double check that your settings have not shifted.
* Replace the cover over the points assembly, if any.
* Reinstall the flywheel and associated hardware and tighten to the specified
torque (30 to 33 ft-lbs). Make sure the cupped washer, if any, has its
cupped-side facing the flywheel. (Defer tightening to full torque if the
engine is not presently mounted solidly on the equipment. Just don't
forget!)
* Check, and if necessary, adjust the magnet to magneto coil spacing using
a non-magnetic (preferably) feeler gauge or shim stock (typically .015
inches though some are .005 to .008 inches, see your engine manual).
* Replace the shroud/blower housing and any trim pieces that were removed
if no other servicing is to be performed on the engine.
Broken starter ropes or failure to retract are both repairs that are fairly easy. However, the spring can be nasty as it is under tension (or should be when reassembled). This can be risky if you are not familiar with the internal construction as you disassemble the unit. The cause of a broken cord is obvious. The cause for a failure to retract could be a broken spring, tangled or frayed rope, or some other mechanical failure. A broken spring will require total disassembly of the starter mechanism - fortunately there really isn't that much involved. With some designs, it is possible to replace the cord without fully disassembling the starter mechanism - by threading the cord in and tying a not in the end - but after rotating it several turns to put the proper tension on the spring. This is relatively safe but may be frustrating as 3 hands are sometimes needed. Where safe disassembly is not obvious, I would recommend that you refer to a book on lawn mower or small engine repair from the library or the service manual for the mower, if possible. You may be able to find specific step-by-step instructions which will minimize your risk of injury from an encounter with an uncontrolled spring.
Should the tubular handle on your mower break at some point (yes, I know this should be unlikely but I know someone who managed to do it), the use of a splint is probably the best approach. Obtain a length of steel pipe with an inside diameter just a hair larger than the outside diameter of the handle. About 8 to 12 inches should be enough. Even electrical conduit may work. Use this to splice the joint. Drill holes through both the pipe and handle and secure with sheet metal screws. This will maintain the required strength and keep the handle the same length as it was originally so you will not have to become a midget to mow your lawn.
"I Recently inherited a BobCat Snow Blower from the 60's or 70's. It has a Lausen 3.5hp (HR35P-2403P). I just installed a Tecumseh Rebuild Kit#631893. The unit runs way too rich, I run out of gas in 10 minutes, the muffler starts to glow red. I cannot get it to idle. I installed a new needle, seat/jet and diaphragm. During the rebuild I did not remove the welch plugs. I tried swapping the idle screw with the high speed screw (not sure which is which). One screw has a smooth taper while the other has a taper with a step to it (no evidence of scoring). Could I be missing a key piece that regulated fuel flow? The rebuild kit did not come with directions, so I just installed everything in reverse." The idle mixture screw is the one with the step. I assume you have any choke off, throttle connected properly with spring return, etc. What happens if you close both idle and main jets? Does it starve? I would expect that you should be able to stop fuel flow totally. If this is not possible, your needles or something else is incorrect/worn or fuel is somehow bypassing the jets which is also wrong. Did you compare the old and new parts to make sure they gave you the correct kit? It also recommend removing the Welch plug and blowing compressed air through the passages to clean. It might also be a problem in the diaphragm spring pressure but without seeing it, no way of knowing. The diaphragm acts against atmospheric pressure. There is a spring on the inlet needle which if missing would run very rich. Chilten has a detailed diagram - really no way of knowing if your assembly was done correctly. Also, warns again using harsh cleaners on non-metallic parts and clearing all vent holes. However, I rather suspect that comment about running rich is not correct as an engine running very rich would lack power if it continued to run at all. Your throttle may be stuck wide open and it may be over revving. Your public library should have some Chilten or other books like those listed in the section: "References". These should include diagrams of the diaphragm type carburetor.
This chapter deals with the following: * Indications for the need for an overhaul. * Engine disassembly down to the last nut. * Inspection of major parts for wear and damage. * Basic replacement or repair of any broken or damaged parts. * Engine reassembly. * Post overhaul testing. For detailed instructions on valve grinding, cylinder reboring, or main bearing reaming, for example, you should refer to one or more of the books listed in the section: "References". However, this chapter will give you the general feel and basic information needed to perform many common types of simple overhaul operations and to evaluate the need for more drastic action - such as a trip to the new lawn mower store! Depending on your particular problem(s), only a subset of these sections may apply. For example, inspection and cleaning of the valves and combustion chamber - even valve regrinding (but we said we weren't going to talk about that!) can be done with a minimum of engine disassembly.
Many common problems can be remedied without going into the deep dark recesses of the engine. However, some will require either a partial or total overhaul. Eliminate all other possibilities from consideration before considering an overhaul - it will not be a fun afternoon (or weekend, or week, or month,....). The following are indications that at least a partial overhaul may be needed: * Mechanical damage - broken, damaged, or bent parts resulting in inability to start or even turn the crankshaft for starting or excessive vibration while running. In most cases, this will be obvious - the mower died very suddenly - possibly with a loud clunk or p-ting and now the crankshaft hits something really really solid inside when attempting to pull the starter. * Low compression - this is due to wear or abuse (lack of oil) of parts like the rings or valves or due to a blown head gasket. Perform the compression test described in the section: "Compression testing". Symptoms would be difficulty in starting and unusually little resistance when pulling the starter cord, and perhaps, loss of power once you get it started. If rings are bad, there may be excessive oil consumption and blue exhaust smoke. If only the valves are involved, only the cylinder head may need to be removed. * Excessive oil leaks - a failure of the oil seals (the lower one on mowers at the PTO/blade end, most likely) will result in oil dripping or pouring from under the mower deck. The blade will be coated with oil and there will be a puddle where the mower is stored. Of course, if this is severe enough or neglected, you may end up with much more serious problems when the internal parts fail due to lack of lubrication. Replacing an oil seal is not difficult. The old seal is removed by piercing its thin metal shell with an awl or ice pick and carefully prying it out. Take extreme care not to scratch or dent the mounting surface or crankshaft. This may be possible without extensive disassembly. The new one is then pressed on. In fact, installing the new seal is best done with the crankshaft in place as there will be less likelihood of damage to the new seal and it can then be driven in straight. There is a special tool for this but a piece of pipe that just fits over the crankshaft cut off square will work just as well. Remove any burrs on the crankshaft to prevent damage to the new seal and take care that any rubber lip on the seal does not get folded over. * Excessive noise - knocking, banging - while an engine powered piece of machinary is not exactly quiet, there should not be unusual or excessive mechanical noises. Such noise can be an indication of an excessively worn engine or of some part that is about to fail. Should you strip the engine based on this? I cannot say - it is a judgement call. It something about the sound suddenly changed, then investigating the cause is certainly warranted. In some cases, multiple problems may be present and/or there may just be excessive wear of parts like the cylinder, rings, and piston. Under these circumstances, the cylinder may need to be rebored to accept a replacement oversize piston and ring set. The cost of the parts and labor (you really don't want to rebore a cylinder) will likely be more than you want to spend. This is when a new engine or mower is the best option.
While the specific question dealt with a medium size snowblower engine, the comments should apply to other yard equipment as well. "Is it economical or feasible to properly rebuild a 7 HP Tecumseh engine on a snowblower? Compression seems fine. Has been burning oil to some degree for the last 3yrs, but this year its' burning a lot - maybe 1/2 pint oil for each gal of gas. Until last year, was using 5W30. This year, switched to straight SAE30. I could get a new Tecumseh SnoKing engine for about $350 including shipping." (From: Mother (jmg14213@earthlink.net)). As a finalist in the All-American Engine Repair Championships formerly held at the Outdoor Power Equipment EXPO (an industry trade show) in the Tecumseh division, and as a Briggs and Stratton Master Service Technician, it has been my experience that: 1. Yes it is POSSIBLE to rebuild one successfully, although if it is not an HH model with cast iron bore, it probably will not hold up (single H models are aluminum bore). 2. It is not cost effective to do so. 3. Short blocking this engine requires special tools if it is more than ten years old, as the ignition timing is not fixed, as it is on newer, solid state models. 4. Engines from companies like Northern Hydraulics may be adaptable to your unit, but will likely not just bolt on. If this engine is on a top of the line product, such as Ariens, Snapper, or BearCat, it is probably worth repairing, as a new comparable product is big bucks (and overpriced). If this engine is on a mid-range product, such as Toro, Simplicity, John Deere, Husqvarna (European product, not USA built), etc., then repair is probably still a good option, due to the overpricing of similar replacement products. If it is on a Murray, Noma, AMF, Dynamark, Ultra, Sears, MTD, YardMan, White, Husqvarna (USA built by Murray/Noma), or other discount store brand, go buy a new machine. The cost of a new unit is not much more than the cost of the engine repairs, and then you won't have a worn out piece of discount store equipment to break down again in three weeks when something else goes bad...
Special compression gauges are available at auto parts stores or small engine parts suppliers. These will catch and hold the highest pressure reached so you don't need to be in two places at once. Note that this procedure may always yield a very low reading if there is a compression release mechanism on your engine - which is very likely. In this case, the crankshaft must be spun in the opposite from normal direction by the flywheel (counterclockwise when viewed from the flywheel end, with the starter removed). * If the compression gauge has a screw thread, install it in the spark plug hole so it snug - it doesn't need to be really tight. If it just has a rubber boot, have a buddy hold it in place in the spark plug hole as you perform the following tests. * Pull the starter cord several times or use the electric starter in the normal manner. * New Tecumseh engines should have a compression reading of at least 80 psi. If your reading is at least 60 psi (or the specification found in your engine manual), then compression is acceptable. * If it is less than expected, squirt a small amount of engine oil in through the spark plug hole so it coats all around the edge of the piston and cylinder. * Repeat the compression test. * If the pressure reading is now acceptable, then the rings need replacement or the piston/cylinder are excessively worn. If there is little change, there is a valve problem. * If the measurement is very low under both conditions, there may be a a blown head gasket or damaged (punctured) cylinder or head. (Or your engine has a compression release mechanism which is reducing the reading - see the note above). For Briggs & Stratton engines, the manufacturer simply recommends spinning the crankshaft by the flywheel in the opposite from the normal direction with the normal spark plug installed. A sharp rebound (as it compresses the trapped air since the compression release mechanism is not active in reverse) indicates good compression. Little or no rebound indicates low compression and need for service.
Only you can decide if the time and effort will be worth it. If you enjoy a challenge, then engine overhaul may be for you. However, this is probably not going to be your idea of fun. Doing something like this for the first time *will* result in scraped knuckles and the liberal use of 4 letter expletives. If the mower was a Hechinger's $100 special and has seen several seasons of use, then it may be time for a new one. If you are not the detail oriented meticulous type, you may be better off leaving this sort of overhaul to a professional or buying a new engine or mower. Most parts must go back in exactly the same orientation as they were originally - including matching of timing marks on the crankshaft and cam gears. Even the piston is not symmetrical - though this is not obvious except by taking detailed measurements. Nonetheless, it will not work well if at all, or will wear quickly if rotated 180 degrees upon reassembly. Furthermore, once a wear pattern has developed, it is generally a good idea to replace parts in exactly the same position - the direction of the piston (wrist) pin or location of the intake and exhaust valve lifters. Violating this rule won't result in immediate failure but could lead to excessive wear and reduced life What this means is that you cannot assume anything about the parts you remove. Even if they look identical at first glance, they may have a definite right and wrong orientation and/or may want to be replaced in exactly the same location. Even lowly head bolts may be of different lengths. Make notes and diagrams. Most of these will be pretty simple but they will save your hide in the end! Bearing surfaces are very finely ground and polished - just dinging the crank pin journal surface against a steel part will put a nick in the relatively soft bearing which will need to be carefully removed as best you can - affecting as little else as possible - with very fine emery cloth. In addition, if you don't like to get your hands dirty and oily, forget it. You will have disgusting black crud under any surviving fingernails for days. This is a messy operation! The outside of the engine will be coated with decayed grass clippings, dust, and dirt. The inside of the crankcase will have the remnants of old used motor oil (also a carcinogen) and the combustion chamber will be coated with filthy carbon deposits. At the same time, cleanliness is critical when reassembling as any particles of dirt or metal will find their way between rotating parts resulting in excessive wear or worse. Having said all that, overhauling a small engine is not like overhauling an automobile engine. In the words of a colleague: "It's just a frick'n lawn mower". What this means is that you can get away with tolerances, imperfections, and mistakes in dealing with a small engine that would be unacceptable for the health of your Chevy or Porsch.
For most of the procedures described below, the basic set of items listed in the section: "Tools and supplies" will suffice. However, some of the following more specialized tools may be needed depending on how far you go: * Micrometer - many of the measurements of wear to engine parts requires determining the diameter of shafts or bearing surfaces. Except for the piston, most of these can be accommodated by a micrometer with a maximum opening of 1 to 1-1/4 inches. However, in many cases, what is important is not actual diameter but clearance - and this can be determined with the inexpensive 'plastigauge' or a substitute. * Plastigauge - these are disposable pieces of calibrated plastic used to determine the critical clearance between the rod bearing and crank pin journal. You place one in between the rod bearing and crank pin journal and tighten to specifications. When removed, simple measurements on the markings on the squashed plastigauge will very precisely determine the clearance, taper, and out-of-round specifications for your bearing. It is also possible to obtain most of this information by using slips of paper or foil of known thickness but this will not be as accurate or convenient. * Flatness gauge - a good machined straight-edge and a set of feeler gauges will suffice for checking the mating surfaces of the cylinder and head. * Ridge reamer - the 1/8" or so above where the piston slides in the cylinder will develop a buildup of carbon. In addition, if the engine has seen really heavy use, the metal in this area will be higher (less worn) than the section below. In order to remove the piston, this ridge must be eliminated or else it either won't come out or you risk breaking the rings. Fortunately, the metal ridge is rarely a problem on lawn mower engines and the carbon ridge can be removed with a simple homemade tool which is just a soft metal (i.e., aluminum or brass) piece with a straight edge or inside right angle. You probably will not need an expensive commercial ridge reamer tool. You will not need one at all unless you will be removing the piston. * Piston ring compressor - when reinstalling the piston and rings, it is virtually impossible to squeeze the rings together to fit into the cylinder without some help. Commercial piston ring compressors are available for about $5 or you can make your own from a large hose clamp and strip of sheet steel (say, 1" x 12" x .020"). This tool is not needed unless the piston is being removed from the cylinder. * Piston ring expander - this allows the easy removal of piston rings from the piston. With care, you can do this by grabbing the two sections of the ring and guiding it off the piston by hand. In any case, unless you will actually be removing the rings from the piston, this tool will not needed. * Valve spring compressor - in order to remove and reinstall the valves, their rather powerful spring must be squeezed together tightly. This is almost impossible to do without this tool. I have done this with an improvised clamp designed for holding lab equipment but it was barely up to the task and not fun. However, unless you are going to remove the valves, this tool will not be needed. * Rubber mallet - the engine overhauler's 'persuader'. In particular, to break free the crankcase/oil sump joint and for reinstalling the piston using the piston ring compressor. A small one will be more than enough. * Scrapers - to remove built up carbon deposits and stuck gasket material - start with a strip of aluminum. For stubborn deposits, a flat edge paint scraper or straight blade screwdriver will come in handy. Take care not to scratch any machined surfaces. Coarse steel wool can then be used to finish up after the major deposits have been removed. For fine work, an X-acto knife also is useful. * Wood blocks (4" x 4" x 8" typical) for supporting the engine on your workbench. * Rags, paper towels, and more rags. Just make sure to dispose of oil soaked material safely. Plenty of old newspaper to protect the ground or table top.
Once the gasoline and oil is drained, all overhaul work can be done indoors. Without gas, there is little risk and working indoors is generally much more convenient. Therefore, you need to decide where to set up for the overhaul. The best location will be relatively dust free, well lit, and not likely to be required for other purposes. Your engine may be remain in a disassembled state for some time if you need to obtain replacement parts. Also, even with its bodily fluids removed, an old engine will stink. Therefore, the dining room table is probably not the ideal choice! Lay out a healthy layer of old newspapers to protect the workbench from oil and solvent drips and damage from heavy tools and parts.
The following description applies directly to a large number of Craftsman mowers using Tecumseh engines (most do). However, with minor modifications, it is also applicable to most other mowers using 4 stroke engines. Mechanically, 2 stroke engines are very similar. In many respects, they are simpler having no camshaft operated valves or oil pump. There is no oil to drain or change. However, needle bearings are used in key spots which complicate matters slightly. Refer to one of the books listed in the section: "References" for detailed 2 stroke overhaul procedures.
While for certain repairs it is quite possible to work on the engine while still mounted on the mower or other yard equipment, it will almost always be much more convenient to disconnect and remove the entire engine to the convenience of your workbench. There are generally only a handful of actual connections. A typical small engine is remarkably light and compact once stripped of the mower deck! * Disconnect and secure the spark plug wire. * Drain the gasoline or remove the fuel tank and store in a safe place. * Drain the oil from the crankcase/oil sump. While this is not essential for all overhaul operations, it will eliminate any risk of oil pouring out or going where it should not when you turn the engine over or on its side. In addition, this further reduces the risk of explosive fumes which might result if excessive gasoline has contaminated the oil. Finally, now is a good time for an oil change! Refer to the section: "An oil change isn't really a big deal". You won't be refilling until later, however. Don't reuse the old oil even if you recently changed it and dispose of it in an environmentally friendly manner. * Brush or vacuum off the exterior of the engine above and below the deck and then wipe it down with an old rag to remove decayed leaves, grass clipping, dirt, oily grime, dead (or live) rodents, whatever. The cleaner it is when you actually start work, the better off you will be and there will be less chance of contaminating the interior. * Detach (and label if there is any doubt about how they are connected) any throttle or dead-man control cables. * Remove the blade (or anything else driven by the crankshaft). See the section: "Non-violent blade removal". Don't lose the locking key if it is separate! * Remove any auxiliary drive (self propelled) or power take off. This may be a belt or chain above or below deck. * Disconnect any electric start wiring from the mower. * Check for and remove anything else that would prevent the engine from being detached from the equipment.
At this point, the engine should be free of all its attachments to the mower except for its mounting. For a typical rotary mower, there will be three large bolts accessible from under the deck. Removing these with the proper socket will allow the engine to be lifted and moved to your workbench. You you will probably be surprised at how light it is! I recommend just screwing the bolts back into their threaded holes finger tight. That way they will not get lost and the threads will be protected. Also, Protect the threaded end of the crankshaft with a bit of rag or paper towel fastened with an elastic band.
The following sections provide the detailed procedures for disassembly and initial inspection for major damage. As noted, these apply directly to most Tecumseh engines but most other 4 stroke engines are very similar.
Now it is time to get down to business! As noted, depending on your situation, not every step will be needed. * Remove any trim pieces which cover the engine. Depending on how much you paid, the engine may be nearly bare or have multiple plastic doodads covering up what is essentially that same bare engine! * Remove the gas tank if you have not done so already. A spring loaded screw clamp may be used to attach the fuel line to the tank - use a pair of pliers, socket, or screwdriver as appropriate to loosen it. * Remove the oil filler pipe, if any. This is usually fastened to the shroud/blower housing with one or two small screws. Thread these back into their holes finger tight so they will not get lost. * Remove the shroud/blower housing. This is usually fastened with 4 small bolts (they may be different sizes - replace in the threaded holes so they will not be lost. If there is a primer tube running to the carburetor, disconnect it at whichever end is convenient. * Remove any electric starter components - starter motor, gears, etc.
* Detach the throttle control (may not be present on all models). Two screws hold it to the carburetor. Replace these screws so they will not get lost. (Yes, I know this is getting kind of repetitious!) * Disconnect the stop wire if there is one. * Use a large philips screwdriver to loosen the two screws fastening the intake pipe to the cylinder block. If the gasket separates easily and cleanly, then it can be reused though a dab of non-hardening sealer is advisable. If it tears or is damaged in any way, then it should be replaced. If the bolts are really tight, an open end wrench may be of help but common sockets may not fit around the bottom bolt. Thin walled sockets may work. * Disconnect the throttle linkage and governor spring noting which holes they go in. IMPORTANT: If you get this screwed up you could have a runaway situation on your hands when you go to restart it. This can destroy the engine in a few seconds! The carburetor can now be set aside or disassembled and cleaned. (See the section: "Cleaning Craftsman (Tecumseh) carburetors". WARNING: there is still likely a significant amount of gas inside the float bowl. If turned on its side or upside-down, this gas will come gushing out. Therefore, it is best to set the carburetor aside in an outdoor area in an upright position. Plug the intake manifold and fuel pipe with wadded up paper towels or rags to prevent the entry of dirt.
Note that in addition to decreasing the noise from your engine, the muffler serves a very important spark/flame arresting function. Therefore, it is important that it be in good condition. Some mufflers simply screw into the cylinder using pipe threads. Others are mounted with a couple of bolts. * Remove the muffer. Use penetrating oil (e.g., Liquid Wrench or WD40) if the mount is heavily rusted or corroded and does not yield to normal efforts. * It is ok to ruin the muffler in the process. Mufflers are inexpensive and you probably needed a new one anyhow. Just do not damage the cylinder threads as the metal is relatively soft. * If the muffler comes off intact, inspect for serious corrosion, holes, or other damage and figure on replacing it if needed.
* If you will need to remove the crankshaft or get under the flywheel to check or adjust the points (non-electronic ignition), then now is as good a time as any to remove it. See the section: "Flywheel removal". * Inspect the flywheel and set it (and associated washers, starter clutch, etc.) aside in a safe place - away from steel filings that will be attracted to the powerful magnet! * Thread the flywheel nut back onto the shaft and then protect it with a rag or paper towel secured with an elastic band.
This can be left in place but will be susceptible to damage. * Inspect the high tension lead for cracking or broken insulation. Temporary repairs using several layers of electrical tape may be made but replacement is best for long term reliability. * Inspect the stop wire and any others for similar damage and repair or replace parts as needed. * The electronic (e.g., Goldkey or Magnetron) ignition can be removed as a unit since there is nothing under the flywheel except possibly a (plastic) sleeve/spacer. Inspect the potted unit for cracks or other damage. * For point type ignitions, the magneto coil along with the components under the flywheel (points, condenser, cam) can be easily removed if the flywheel has been pulled. Inspect for worn, pitted, welded, or corroded points and other damage.
* Use the proper size spark plug or deep socket to remove the spark plug counterclockwise. Inspect the spark plug and threads in the head for damage. * Use the proper size socket to remove the (usually 6 to 10) head bolts counterclockwise. It is best to loosen each a half turn at a time in an alternating pattern until they turn freely to minimize possible stress on the head. They will be fairly tight but should not be frozen. Check each one after removal as some may be longer than others and then must go back in their respective holes. Hold the head with one hand as you remove the last couple bolts - it should pop right off. * Separate the head and head gasket from the cylinder. This should occur easily without requiring your persuader. * Inspect the head, head gasket, and cylinder mating surface for major damage. While it may look really ugly, once the carbon is removed, the metal should be virtually like new. * Remove built up carbon from the head, valves, piston, and cylinder. This is best accomplished by chipping it away with a soft metal tool like a scrap of aluminum. Take care if you use a steel paint scraper or screwdriver not to scratch the relatively soft cylinder or piston. WD40 will often help to loosen this carbon buildup. Most of the carbon will probably be on the exhaust valve and on the exhaust valve side of the head and piston.
You should only need to do this if you are replacing or grinding a valve. In most cases, the valves are undamaged but may appear in poor condition due to carbon buildup - which can be removed in-place fairly easily. * Remove the valve cover on the side of the engine next to the valves. * Use a feeler gauge to check the gap between the valve lifter and valve stem with the valve lifter in the relaxed - lowest - position. A typical value is .010 inches. Excessive clearance will require replacement of the valve or valve lifter. * Use a valve spring compressor to remove pressure on each valve. * The retaining clip or split cup should now be free. Remove these. * The valve should now slide out. * Loosen the valve spring compressor and remove the spring and any other hardware. Don't interchange the intake and exhaust valve springs. * Remove the built up carbon deposites from the valves and valve seats using a soft metal scraper. Some WD40 may help to loosen the caked on carbon. * Inspect the valves for serious burning or pitting especially on the seating (angled) surfaces. Once free of any carbon, they should be smooth and undamaged. * Similarly, inspect the valve seats for serious burning and pitting. * Inspect the springs for rust or other damage. Stand them on a flat surface and check for serious droop/tilt. Measure their free length and compare with your engine specifications.
We are now going into the lower section. I can hear you saying "Joy!". * Check the crankshaft for burrs at the blade lock key or other key and/or where any front wheel drive pulley setscrew was tightened. It is essential that these be carefully removed with a fine file before you attempt to remove the cover to avoid damage to the main bearing. In addition, any rust and/or dirt buildup must be removed with steel wool, sandpaper, or emery cloth to allow the shaft to pass through the main bearing without damaging the bearing or oil seal. Remove all traces of rust and grime but don't go overboard - it doesn't need to shine. Wipe with a very slightly damp cloth to remove **all** abrasive residue. * Set the engine flywheel-side down on wooden blocks so that the flywheel mounting shaft is clear of the table. * Once again, wipe down the underside of the engine, especially around the crankcase/oil sump mounting bolts and the seam where the cover will separate from the engine block. * Remove the 6 to 10 hex head crankcase/oil sump mounting bolts and set them aside. * Use a soft rubber mallet if necessary to help free the cover. If mild persuasion doesn't work, check for any bolts you may have missed. * As the cover comes free, gently lift and turn at the same time. It should slide right off the crankshaft. If there is any resistance, you probably didn't find all the burrs or rust. Go back, identify, and correct the problem. Don't force it as you will end up with scratches on the bearing surface and/or damage to the oil seal. * The gasket will likely tear in the process of removing the cover and will need to be replaced. It is not worth trying to repair it. You will have to scrape the remnants of the old gasket off of both mating surfaces before installing the new one (later). * Check for any washers that may come free with the cover. There will be at least one on the crankshaft. It may be sticking to the bearing surface on the cover. * Usually, the flyweight governor is just left in place unless parts need to be replaced. Inspect it for damage to the gears, flyweights, or cup. Individual parts can be replaced if needed (and if you can get them!). The post is a press fit and should not be disturbed unless damaged.
* Remove the camshaft driven plunger type oil pump. This is in two sections which have a definite relationship (the flat faces out). Inspect for damage and set aside. * Carefully rotate the crankshaft until the timing marks align. These will be a line, dot, or hole on the camgear and crankshaft gear. For most engines, these should line up perfectly with each other at one position of the crankshaft. However, on some Craftsman engines, they are offset by one tooth. Check and note this before removing the camshaft/camgear! * With the timing marks aligned, valve pressure should be released (if you removed the valves, this won't matter) on the camshaft and it should slip out easily. * Inspect the camgear for chipped or broken teeth and wear. There should be no chipped teeth and no detectable wear on any of the gear teeth. Chipped teeth or significant wear will require replacement. * Inspect the cam lobes for wear or wear. There should be no detectable wear and no damage. * Check the compression release mechanism on the camgear for damage and free operation. The weight should snap back to the shaft when released. The little lift pin should move smoothly. * Remove each of the valve lifters and inspect for wear. There should be no significant wear. Note which went where so that they can be replaced in the same location. Most are of the same length but once a wear pattern is established, replacement in the same location is desirable. Sometimes, they are of different lengths and then this is more critical.
* Rotate the crankshaft so that the rod bolts or nuts are accessible. * Bend out any lock plate that may be associated with the rod bolts or nuts. Many Tecumseh engines use 'Durlock' rod bolts with integral locking serrations and there is no lock plate and no lock washers. Note: Durlock bolts, lock plates, or lock washers should always be replaced with new ones if removed and not be reused. You really don't want the rod coming apart! * Use the proper size socket to loosen the rod bolts or nuts counterclockwise. Start with small equal increments on each of them until loose to equalize stress. * Remove the bolts or nuts and cap. Note the orientation of the cap and rod. If yours is the slant type, this is easy. Otherwise, look for match marks, casting numbers, or other identifying marks and make a diagram in any case. * Where bolts protrude from the rod, immediately cover these with some bits of rubber tubing or tape to prevent them from hitting and dinging the crank pin journal or other precision surfaces.
* Remove any carbon ridge you find at the top of the cylinder. This will catch the rings and prevent you from removing the piston or if force is used, break the rings. Usually, it is a simple matter of scraping with a piece of soft metal like aluminum. On rare occasions with a really well worn engine, enough of a metal ridge will also be present to require the use of a ridge reamer tool. * Push the piston up and out of the cylinder bore. The rings will expand but will not pop off unless they are actually broken. * Replace the rod cap and finger tighten the nuts or bolts. This will help to protect the bearing surfaces from accidental damage. * Inspect the piston for damage. There may still be significant carbon deposits but once these are carefully scraped off, the piston should be fairly smooth. There may be some vertical scoring but a modest amount of this is not serious. * Inspect the rings and ring grooves for damage. It is usually not necessary to actually remove the rings from the piston to do this - which should be avoided if possible to minimize the chance of breakage. The outer surface of the rings should have an almost polished appearance with no significant pits, scratches, or corrosion. There should be no chips or other visible damage. * If you must remove the rings, use a ring expander if possible and make sure you note the exact orientation - top/bottom and location - for each. * If you are removing the piston pin, note the orientation of both the rod and pin as they must be returned in the same relationship. Pistons are not symmetric! Look closely and you will see that the pin is offset a fraction of an inch to one side. This is done to optimize the center of force on the rod bearing and rotating crank pin journal. * Use a pair of needlenose pliers to remove the 'circlip' from one side. The piston (wrist) pin usually floats (moves easily) in between the two circlips but a slight lip of metal (probably resulting from the pin banging back and forth) may prevent it from being easily removed. Very slightly scraping around this lip will free it up or you can remove the other circlip and then use a drill or arbor press to push the pin out far enough to free the rod. There is no need to remove the pin entirely. Then, there will be no question as to the direction upon reassembly.
* Lift while rotating the crankshaft out of the top bearing. There should be no resistance (unless you forgot to remove something). * Inspect the crankshaft to determine if it is bent. Any deviation from perfection is cause for replacement. The proper way to do this is with some V-blocks and a run-out gauge. However, you won't have these tools so a visual inspection is the best you can do. However, unless your blade kissed a boulder, a bent crankshaft is not likely. * Inspect the small gear for broken teeth and wear. There should be no chipped teeth or detectable wear of the gear teeth. If there are chipped teeth or significant wear, then this gear and the camgear will need replacing. Note: the small gear on the crankshaft may be a press-fit and may not be considered serviceable by itself without replacing the entire crankshaft. However, I have been able to remove it non-destructively by gently tapping on each side using a soft metal bar (e.g., brass) and a small hammer. (When I had to do this, the guy at the engine parts store was surprised that I was able to get it off without damage.) Heating the replacement gear will expand it and reduce the force needed to press-fit it onto the crankshaft. Similar gentle tapping will then work once the gear is aligned with the indexing pin. * Check for any washers at the flywheel end of the crankshaft and set these aside. There are probably none.
* The breather allows the pressure inside the crankcase to vent to the outside and should result in negative pressure inside as this contains a (leaky) one-way valve. * The breather cover is under where the flywheel is located. * Remove the screw to remove the cover plate. There is a gasket but it will probably separate cleanly. * Check the spring and valve disk for rust, dirt, and wear. They will likely be fine. Make sure the small vent hole is clear. * Replace the cover as there is nothing else to do in there.
* Do not remove the oil seals unless you intend to replace them. If oil leakage has not been a problem and you don't think any damage resulted from removing the crankshaft, leave them alone. It should be possible to replace the oil seals after reassembly if oil leakage turns out to be a problem. * It is very unlikely that the flywheel side oil seal would be defective or damaged. * The PTO/blade oil seal can be damaged by neglecting to completely remove burrs from the crankshaft before removal of the crankcase/oil sum cover. * To remove the oil seals, use a screwdriver to pry them out from the crankcase/oil sump cover and/or the flywheel side of the crankcase. Take care not to gouge the mounting surfaces.
A complete overhaul can restore a small engine to like-new condition. Any
parts that are found to be damaged or out of tolerance are repaired or
replaced.
Determining this requires a visual inspection and taking measurements of
all critical dimensions of bearings, cylinder, piston, and rings. Some of
the inspection is subjective - how badly scored a bearing surface is before
it must be replaced or reground. A few score marks around the circumference
of a bearing surface will not adversely affect operation or wear. How few
is a few? Perhaps if less than 10% or so of the surface is affected. You
are not going to spend as much to repair the mower as it cost in the first
place in any case so don't lose sleep over it.
Measurements may come up marginal as well. For example, if the limit listed
in your engine specifications is .0015" and you measure .002" will this be a
serious problem requiring the replacement of expensive parts? Probably not.
You may get less than optimal life out of the engine but it will probably
still work fairly well and for a long time. So many other factors can affect
life that this may have no effect at all.
The following items should be visually inspected. If any significant wear
is indicated, precise measurements should be made:
* Crank pin journal and rod bearing. Inspect for wear, pitting, and scoring
on both the crank pin journal and the inside bearing surface of the rod and
cap. On a new engine, both of these surfaces are nearly mirror smooth. On
a well worn engine, there may be significant scoring due to particles from
the oil getting trapped. An engine that has failed due to a severe lack of
lubrication may result in some pretty spectacular failures of these parts.
Minimizing wear and the change of catastrophic failure is the primary reason
for performing regular oil changes.
- A few score marks around the entire circumference of the journal are
unimportant as long as they represent a small percentage of the surface
area.
- Scratches, pitting, or score marks that run side ways are more serious.
If slight, polishing with very fine emery or crocus cloth may be all
that is needed. If they catch a fingernail, this may not be enough.
- A serious out-of-round condition is unacceptable.
Follow the instructions that came with the plastigauge to take measurements.
Consult your engine specifications for acceptable limits. Use judgement
in determining whether slight out-of-spec measurements will necessitate
replacement or major rebuild.
If you had a rod failure due to lack of oil (remember what we said about
the importance of oil - see the section: "Rod disasters - or why the oil and governor are kind of important") - then there could be a variety of
types of damage that will make these measurements academic. The rod my have
broken in half or the cap may have literally exploded into multiple pieces.
In many cases, the crank pin journal will escape relatively unscathed but
needless to say, you will need a new rod and cap - not cheap!
* Main bearing - PTO (blade) end. Inspect for severe scoring, corrosion,
or other damage. It may no longer be mirror smooth but should not appear
excessively worn.
* Main bearing - flywheel/magneto) end. Inspect for severe scoring, corrosion,
or other damage. This will probably appear almost like new even on an old
engine as there is a lot less load on this end and it is relatively well
protected and well lubricated.
* Cylinder. Inspect inside the cylinder for excessive wear and scoring.
If it appears fairly smooth without much scoring, it is probably ok
but only exact inside measurements would confirm.
* Piston. Examine the sides for vertical scoring. There will probably be
some but as long as the piston is not mostly score marks, it is probably
fine. Only exact measurements would confirm. Check for damage to the
lands - the surfaces between the ring grooves. If any are cracked or
broken, the piston will need to be replaced.
* Piston (wrist) pin. This should be mirror smooth. There should be no
detectable free play if you try to jiggle the rod.
* Rings. Inspect for damage, pitting, and scratches. The outside surfaces
should be pretty much mirror smooth. Use an appropriate sized feeler
gauge to check clearance between the rings and piston grooves.
* Oil passages. Inspect and use compressed air if necessary to clear the
various oil passages in the crankcase/cylinder, camshaft, connecting rod,
and crankshaft. The typical small Tecumseh engine has a hollow camshaft
which is part of the oil pump and drilled passages in the crankcase. The
oil path is from the plunger/barrel oil pump up through the center of the
camshaft, over top via the passages in the crankcase to lubricate the main
bearing (flywheel/magneto end) and also to drip on the connecting rod and
crank pin journal. Some larger engines also have drilled passages in the
crankshaft and connecting rod. There is even an oil pressure test port
normally sealed by a small screw. A typical pressure measurement on an
engine running at full speed is 7 psi but you won't measure this so just
make sure everything is clean and clear.
Once you have performed whatever magic is required to repair or replace
broken or damaged parts, here are the steps that will transform your pile
of parts into a (hopefully) working engine.
If any filing, sanding, or grinding was involved, make sure all traces of
abrasives have been removed from every part. The best approach is to clean
with soap and water or mild detergent and dry thoroughly. Then immediately
coat all ferrous parts with engine oil to prevent rust.
Where the internal moving parts are involved, liberal use of fresh engine
oil will also make things to go together smoothly and help protect the
surfaces from damage due to initial lack of lubrication.
* Oil seals: If you removed the oil seal(s), clean the inside surfaces
where the seals go and install new ones by pressing them in straight and
square with a block of wood and rubber mallet or better yet, use a drill
press or arbor press. Make sure you get the correct side facing out!
Installing the new oil seals after the crankshaft has been replaced may
be easier. There is a special tool for this but a piece of pipe that just
fits over the crankshaft cut off square will work just as well. Remove any
burrs on the crankshaft to prevent damage to the new seal and take care that
any rubber lip on the seal does not get folded over.
* Breather: If this was removed, replace valve plate, spring, gasket, and
cover. However, this is probably already assembled.
* Valves: Use a valve spring compressor to fully compress the spring for the
intake valve and install the valve, any washers, and retaining clips. Do
the same for the exhaust valve. Install the valve cover.
* Piston rings: Replace any that were removed. Use a piston ring expander
if available or your hands to expand the rings and slip them over the piston
and into their proper grooves. Note orientation and position! Avoid
scratching the relatively soft piston. Do not expand more than needed -
the rings are fragile.
Note the typical arrangement (from top to bottom):
- Compression ring (solid).
- Compression ring (solid).
- Oil ring (slotted with internal expander spring).
But, you drew a diagram, right?
Note: if new rings are installed, you should deglaze the cylinder
wall with fine emery cloth in a cross-hatch pattern (diagonal strokes).
This is needed break in the new rings. Then very thoroughly clean the
cylinder to remove all traces of abrasive residue.
* Piston pin and connecting rod: Put a few drops of engine oil on the
pin, position the rod, and then slide the pin into place. Use a press
if it is a tight fit. Use new circlips to secure the pin. Make sure
you get the orientation of both the rod correct! It is also desirable
to install the pin in the same orientation as it was originally. If the
pin was never entirely removed, this should not be a problem.
For the following, position the crankcase flywheel/magneto side down on
some wooden blocks so that when the crankshaft is installed, it's end will
be clear of the table-top.
* Crankshaft: Using a gentle rotating-while-inserting, place the crankshaft
into the flywheel/magneto-end bearing. Use engine oil to prevent scratches.
Take care not to bend over the lip of the oil seal.
* Piston into cylinder: Coat the piston and cylinder wall with engine oil.
Orient the rings around the piston so that the gaps are staggered by 90
degrees and not above the pin location. Suggest from top to bottom: 45,
135, 225 degrees. Use a piston ring compressor (commercial or home-made).
Tighten until the rings are fully compressed and then release just a hair.
Position the piston in the correct orientation - rod with respect to
crankshaft - and gently tap into cylinder using a wood block and rubber
mallet. If it hangs up, the compressor is too loose. If it does not
move at all, the compressor is too tight.
CAUTION: Do not use a metal hammer - there is a good chance you will crack
the fragile aluminum piston.
CAUTION: Don't let the bottom of the rod or rod bolts hit the crankshaft!
Put a wad of rag inside to prevent this.
* Rod and cap to crankshaft: Coat the crank pin journal with engine oil.
Position the crank pin journal and rod bearing so that they are in contact.
Place the rod cap in position - noting match marks. Using a new lock plate,
lock washers, or rob bolts, as appropriate, hand thread the nuts or bolts on
as far as they will go. Jiggle the cap to adjust and then tighten some
more by hand.
CAUTION: double check that you have the match marks aligned. If correct,
the bearing formed by the rod end and cap will fit the crank pin journal
perfectly - seated fully - with no free play even when only finger tight.
If you attempt to fully tighten the rod nuts or bolts and the cap is
backwards, you may ruin the rod and cap by distorting the soft metal.
Now, use a torque wrench to tighten the nuts or bolts to the proper torque
as listed in your engine manual. Alternate between the two nuts or bolts
tightening in small equal increments until the proper torque is reached.
Where a range is specified, aim for the middle.
Where a lock plate is involved, torque to the middle of the acceptable range
and then tighten the nuts or bolts just enough further to align a flat with
the edge of the plate. Then, bend the plate over to lock it in place. DO
NOT reause an old lock plate.
It may be a tight fit to get a torque wrench inside the crankcase. Here are
a couple of comments:
- I use a basic 3/8" deflecting beam type torque wrench - nothing fancy.
To this, I add a 3/8" to 1/4 inch adapter (short) and a 1/4" socket.
- Position the piston/crankshaft to provide the most clearance for each
nut or bolt. These will differ.
- This can also be done with an open end wrench and spring scale but the
torque wrench is so much easier!
It is just possible to get both the clearance and angle to use the torque
wrench effectively. With a ratcheting torque wrench it would be easier but
this is not essential.
THIS ASSEMBLY IS MOST CRITICAL and is probably the single most important
place to get the torque just right. Too tight and (especially for aluminum
alloy rods/caps) you will strip the threads and/or distort the precision
fit. Too loose and the bolts will eventually work their way out. You
really don't want the cap to pop off while the engine is running at full
power!
* Valve lifters: Install the valve lifters in their respective holes.
* Camshaft/camgear: Carefully rotate the crankshaft until the timing mark
faces the camshaft bearing location. Slip the camgear in place so that the
timing marks exactly align (or if your engine is one of those exceptions,
so they are off by one tooth - see your engine manual if in doubt). For
most Tecumsehs:
- The camgear timing mark (if not marked) is in line with the center of the
hobbing hole (small hole in the face of the gear).
- The corresponding timing mark on the crankshaft is either a beveled tooth
on its gear or in line with the keyway.
- If the engine has a Craftsman type (float) carburetor, advance camshaft 1
tooth clockwise (except for the Craftsman variable governed fuel system,
whatever that is!).
* Oil pump: Install the two piece oil pump. The flat must face out.
* Crankcase/oil sump cover (temporary): Install the washer(s) that go on
the crankshaft. Without using a gasket, install the crankcase/oil sump
cover. Use a gentle twisting motion and take care to avoid damaging the
oil seal. Slip the ball end of the oil pump plunger into its cavity in
the cover before it is fully lowered. With a little jiggling, the cover
should seat properly. Thread a couple of the mounting bolts in hand tight
to hold it in place.
* Test for free rotation: Use the blade adapter and key as a means of grasping
the crankshaft and rotate it through two complete revolutions. There should
be no binding of parts though you will feel the resistance of the piston
as it moves up and down in the cylinder and the valves as they are lifted
once in every two revolutions (which you will also see from above).
* Remove the cover. Double check that the mating surfaces are free of old
gasket material and dirt. Use a new gasket. Again, take care not to
damage the oil seal and line up the ball on the end of the oil pump plunger
so that it fits in its cavity in the cover as it is slid into place.
Install all the bolts and tighten in a staggered order incrementally to
the proper torque.
* Cylinder head: Position the cylinder head and new head gasket and install
all the head bolts finger tight. If any are of a different size, make
sure they go in the proper locations so that they do not bottom out or
engage too few threads. (Tecumseh bolts seem to be all the same size.)
Tighten the head bolts in the recommended sequence in 3 or 4 equal
increments to the torque specified for your engine.
Engine repair manuals always recommend using a new head gasket. The old
one has shaped itself to the texture and imperfections of the head and
cylinder and you could never match this up perfectly upon reassembly. The
result can be leakage of hot combustion gases and ultimate failure of the
gasket and possible damage to the mating surfaces.
However, if you have not done anything to the head or cylinder surfaces and
the gasket is in essentially perfect condition, you can risk reusing it but
I won't guarantee long term reliability! My general recommendation is that
you use a new head gasket once you are sure that everything works properly
and thus there will be no need to remove the head again. Unless the old one
is damaged, it will work fine for testing purposes.
A typical Tecumseh bolt tightening sequence is shown below (except 8 HP).
Check your service manual for the specific recommended procedure for your
particular model engine.
Flywheel/magneto end
___________________
/| | | | | | | | 8 |
|5| | | |3| | | |=|=O |
| O=|=|=|=O=|=| | | | |
/| | | | | | | | _ | |
|1| | | | | | | | |O| |2|__
| O | | | | Spark Plug O |
| | | | | | | | | | | | | |
\|7| | | |4| | | | | | | |
| O=|=|=|=O=|=| | |6| | |
/\| | | | | | | |=|=O |__|
___/____\|_|_|_|_|_|_|_|_|_|___\___
-----------------------------------
PTO/Blade end
For the following steps, position the engine on wooden blocks blade/PTO side
down.
* Ignition: Install the components (if any) that go under the flywheel
(e.g., points, condenser, cam). Install the magneto coil or electronic
ignition module. Temporarily position it so that it is as far away as
possible from where the flywheel will go. Tighten the bolts.
* Set the point gap and ignition timing (point type ignitions systems only).
See the section: "Setting the point gap and ignition timing".
* Flywheel: Place any inside spacers proper side up onto the crankshaft.
Position the flywheel key in the keyway and then install the flywheel
onto the shaft. Jiggle it a little to seat solidly. It should not now
move from side-to-side at all. Add the washers, starter cup, and flywheel
nut. Screw the nut on by hand and then tighten securely (but not to full
torque necessarily at this time) using a socket wrench. Torque to
specifications once the engine is mounted as this will be a lot easier.
* Set the flywheel magnet-magneto gap (if you have not done this already):
Place an appropriate spacer (e.g., .015 inches) between the flywheel magnet
and magneto pole pieces. Loosen the magneto coil mounting bolts. The
magnet will draw the pole pieces tight against the spacer. Tighten the
bolts to the recommended torque.
* Install the spark plug with a new washer (and a dab of anti-seize compound).
First, thread the plug in by hand to get it started and then tighten to
specifications (15 to 30 ft-lbs typical).
* Install any electric starting components.
* Install the muffler. A dab of anti-seize compound will make removal of
exhaust system components much easier at a later time should the need arise.
* Carburetor: Position the carburetor assembly in its proper location.
* Reinstall the throttle and governor linkages: Where there is no speed
adjustment or idle position, the direct governor linkage goes in the hole
closest to the engine and the spring hooks onto a fixed vertical metal
strip with only one hole at one end and the lower hole in the governor
lever at the other. Thus, in operation, the spring attempts to keep the
throttle open and the governor pulls on the throttle to close it. Increased
spring tension results in higher speed. Don't get these backwards when you
go to reinstall the carburetor on the engine!!!
* Reattach the primer tube, if you removed it at the carburetor end.
* Reattach the stop switch wire, if any.
* Install the carburetor onto the engine with a new gasket if needed. Tighten
securely to the proper torque (6 to 8 ft-lbs).
* Double-check that the throttle linkage and governor spring are in the
proper holes and nothing is binding - you should be able to move the
throttle back and forth without any sticking or tightness. It should
return to the full counterclockwise position instantly as a result of
the governor spring tension.
It will be easier to tighten the flywheel nut to the recommended torque once the engine has been reinstalled on the mower. Therefore, now is a good time to install the engine to the mower deck: * Remove the three mounting bolts from the bottom of the engine. Position the engine on the mower deck and install these bolts finger tight. Then, use a socket wrench to tighten securely. * Tighten the flywheel nut. Brace the flywheel against something solid and tighten the flywheel nut to the recommended torque (30-33 ft-lbs). * Shroud/blower housing: Position and install using the proper bolts. * Oil fill pipe: Put a little engine oil on the O-ring. Position the fill pipe into the oil hole in the base of the crankcase/oil sump cover. Make sure the O-ring seats inside the oil hole. Tighten the screw(s). * Gas tank: Slip the gas tank into its mounts and tighten any screws. Connect the carburetor fuel hose to the gas tank. * Trim pieces: Reinstall any trim pieces. * Reattach any dead-man and throttle cables to the engine. * Install any front wheel drive components - pulley to crankshaft (using proper key) and belt, or chain drive. * Install the blade adapter and blade. Tighten to the recommended torque. * ADD OIL!!! Add fresh engine oil to just below the top of the oil filler hole or just below FULL on the dipstick. This will be about 1-1/4 pints. * Use the starter cord or electric starter to crank the engine a few times. This will help to distribute the oil. * Add a small amount of gasoline to the fuel tank - say, a half a glass.
Assuming you didn't make any mistakes, the engine should start on the first pull. As you start it, look and listen for any abnormalities and immediately stop it if any are detected: * Engine overspeeds due to screwed up governor or linkage. * Unusual knocking or banging due to parts hitting one another. * Excessive black, white, or blue smoke from exhaust (or 3 foot flames, I suppose). * Overheating. * Leakage of oil or gas. Assuming nothing appears wrong, run it for a while at slow speed (if you have the option). Continue to be on the lookout for anything unusual. After a few minutes, stop it. Let is sit for 10 minutes or so and then check, and if necessary, top off the oil. Now, restart and run it at high. Mow a few lawns. Congratulations! Hopefully, your engine will now serve you for many more years - or until the blade hits the next curb!
The following bulletin can be found at:
http://www.chevron.com/chevron_root/prodserv/bulletin/plastic_fire.html
Filling Metal Gasoline Cans Placed on Plastic Surfaces Creates Fire Danger.
(Copyright 1995 Chevron USA Inc. All rights reserved.)
"Several vehicle fires have resulted at Chevron service stations as a result
of customers filling metal portable gasoline containers (gas cans) placed on
plastic surfaces. The fires have involved a gas can in the back of a pick-up
truck with a plastic bed liner. The insulating effect of the plastic surface
prevents the static charge generated by the gasoline flowing into the gas can
from grounding. As static charge builds it can create a static spark between
the gas can and the fuel nozzle. When the spark occurs in the flammable range
in the gasoline vapor space near the open mouth of the gas can, a fire occurs.
How to fill a gas can to minimize the danger of fire:
* Use only an approved container.
* Do not fill any container while it is inside a vehicle, a vehicle's trunk,
pick-up bed, or on any surface other than the ground. This includes pickup
trucks, sports utility vehicles, vans and others.
* Remove the approved container from the vehicle and place it on the ground a
safe distance away from the vehicle, other customers and traffic.
* Keep the nozzle in contact with the can during filling.
* Never use a latch-open device to fill a portable container.
* Follow all other safety procedures, including No Smoking.
The rotating blades and mass of the internal engine parts pack quite a
punch. Speeding along merrily mowing away one doesn't think about this.
However, if the blade should hit an obstruction, you may have no choice.
There are various safeguards to protect the mower from damage should a blade
tip hit something but these don't always work. Why?
There is protection for the upper and lower parts of the crankshaft after all:
* The soft metal blade lock key can prevent damage due to excessive torque on
the blade-end of the crankshaft when the mass of the engine parts continue
to attempt to rotate after the blade hits something solid. The blade adapter
then breaks away allowing the crankshaft to rotate freely. A 25 cent blade
lock key or a $4 blade adapter will remedy this.
* The soft metal flywheel key will protect the upper part of the crankshaft
and flywheel from damage should the blade and crankshaft stop suddenly and
the inertia of the flywheel attempts to keep it rotating. A 25 cent flywheel
key will remedy this.
In many cases, both of these will break free at the same time.
However, if the shock is severe enough, much more serious damage can result.
Here is why: When one end of the blade hits a curb, for example, the inertia
of the mass of the blade alone (rotating at high speed) will attempt to push
the shaft sideways. This is pretty much independent of the rest of the
engine.
In the diagram below, the blade is rotating clockwise. When the left-hand
tip hits the curb, the right-hand side due to the inertia of the entire
right-hand half of the blade wants to continue to move (down in this diagram)
with the 'X' as the fulcrum. The entire left-hand half section of the blade
contributes relatively little. This results in a net significant sideways
(downward in the diagram) bending force on the crankshaft. The unavoidable
arrangement of the fulcrum at one end and the shaft in the middle makes the
situation even worse as the force resulting from the blade tip (the right hand
one in this example) is amplified by the up to 2:1 mechanical advantage of the
lever arm (the tip is twice as far from X and the shaft).
Blade tip /
hits curb. X-------____________________________________
Ouch! / | | Inertia of this
/ | - O - | | side of blade
/ |____________________________________ | | attempts to
| | | | ------- | continue in same
V v v v v v v direction.
Net sideways force
on crankshaft
While the rotating mass of the engine is attempting to shear the blade lock
key, the inertia of the blade is trying to push the crankshaft sideways.
The net result could be a severely bent crankshaft - a very expensive
repair. An 8 to 10 degree bend is not unusual for a typical Craftsman-class
mower running at full power. Any detectable bend in the crankshaft requires
replacement - it is not safe to attempt to straighten it. A bend resulting
in the blade tips wobbling by more than a fraction of an inch, there will be
unacceptable and dangerous vibration when the mower is run. In addition, the
original trauma (as well as attempting to run with a bent crankshaft) can
damage other parts like the main bearings and connecting rod. The blade lock
and flywheel keys will likely be broken as well but these are insignificant
in comparison to the cost of major replacement parts and the labor involved
in their installation.
The time and effort needed to disassemble the engine is significant and the
crankshaft is probably the single most expensive part of the engine. In
fact, purchasing a new crankshaft may be more expensive than an entire new
lawn mower! It is quite possible that unless you have access to low cost
replacement parts from a salvage yard and have the free time to do the work,
repair may not make sense.
Therefore, don't let this happen to you. Your curbs and rocks don't grow
that quickly and do not generally require mowing!
It is too bad that most lawn mower blades are made of heavy rigid steel (though I do recall a mower that used a super thick nylon cord - sort of like a weed whacker on steroids). The chance of serious engine damage from curb kissing would be greatly reduced if a blade were used which had less inertia and increased flexibility. Then, no matter how hard you tried to whack something solid, only the blade lock and/or flywheel keys would shear and thus spare the expensive engine parts. Apparently, some mowers are made with swing tip blades: (From: Roderick Carmichael (carmic@nex.net.au)). "I use a top notch Supa-Swift with a gravity cast alloy chassis and swing-tip blades (Australian invention, no bent cranks on our mowers mate!)" Why are these not common in America? Conspiracy to sell replacement parts by the small engine manufacturers? :-). You would have to really work at bashing a curb to bend a crankshaft with such a mower. Another possible approach - applicable for both new lawn mower designs as well as field upgrades - would be to replace the heavy steel blade with one made of nylon with a molded-in steel edge. An auxiliary flywheel might have to be added (under the deck) to provide the needed inertia (normally supplied by the steel blade) for the engine to start and run properly and to help the mower plow through tall grass. However, since this additional flywheel could never be stopped abruptly due to hitting a rock or curb, its inertia would never contribute to a sideways bending force on the crankshaft. The greatly reduced mass and increased flexibility of a reinforced nylon blade should virtually eliminate the possibility of a bent crankshaft from such unfortunate incidents. See the section: "Why you really don't want to attempt to move an immovable object".
(From: Forbes Family (fbsfam@clear.net.nz)). I have recently purchased a new rotary lawn mower and appear to have started wrecking it in the first two weeks of use! Problem is, my property has lawns that run alongside a gravel driveway, and its often very hard to guarantee there are no stones lying in the grass before you start mowing. Not surprisingly I often hit small stones. These usually cause no harm, but today some teenagers were mowing my lawns and hit a real monster that measured approximately three inches by two by one, and weighed more than half a pound! Although the mower seems still to work OK, the impact has created a three inch long tear in the mower's cast aluminum body. Not a nice thing to have happen to a new machine! Despite the stone's size, I was surprised at the size of the resulting tear in mower's more than 1/4 inch thick aluminum casing. I hadn't imagined a rotary mower blade powered by a 5HP Briggs and Stratton motor could produce such force! It would be interesting to hear from others who have survived similar experiences and to get an idea from any budding engineers on whether its perfectly reasonable for a stone this size to do such damage to the body of my mower - or whether it's more likely the body casting had a manufacturing defect that made it split prematurely?
A combination of low oil (well, actually, almost no oil) and probably too high RPMs resulted catastrophic failure of the connecting rod and cap on my garage sale Eager 1 Craftsman mower. I had just completed cleaning the carburetor and was testing it when p-ting!! and it stopped dead - the rod had broken and it was dead-dead. Extremely embarrassing since there was no excuse for such a disaster. The primary cause was likely a lack of oil - I should have checked it before attempting to run the engine for more than a few seconds. I have no idea whether someone had actually drained the oil for who knows what reason or it was just very low. In addition, I may have accidentally put the governor link back in the wrong hole permitting the engine to run at an abnormally high (and dangerous) speed. There was no warning. The rod cap just exploded into e pieces (and this was at normal speed) and took a nice chunk out of the interior of the crankcase. Based on a post mortem of the rod, it appears as though one of the cap screws just loosened and backed its way out totally - there was no evidence of thread damage that would be expected if it were ripped out - and fell into the sump. With only one screw holding the rod and cap together, eventual failure was inevitable. Due to the offset design of the cap, this probably worked for a while since most of the force is on the rod. Discoloration indicated excessive heating but no obvious bearing damage was evident that could be attributed to the lack-of-oil condition. The bearing was not in pristine condition but the type of scoring seemed to be more due to just poor general maintenance - lack of regular oil changes - than to this incident in particular. Lessons: Check the oil level no matter what if there is any question or you are working on an engine of unknown history. Double check the governor linkages - take notes during disassembly - and be aware of what a normal speed sounds like for your type of engine (2 stroke or 4 stroke). If in doubt, install the link in the hole that would result in lower RPMs - closer to the carburetor. You can always move it later.
"I tilted my Toro to work on it and now can't start it because oil flooded into the cylinder. I already cleaned up the plug. Is there anything I can do to clean out the oil without taking the engine apart?" Possibly, just letting it sit for awhile (in the normal position!) will allow the oil to drain back into the crankcase sump. If oil is really trapped between the piston and the head, then you may be able to just tip the lawn mower so that the spark plug hole is down (a buddy may come in handy) and drain the oil out through there. Alternatively, you should be able to suck most of it out with a kitchen baster and narrow extension tube (make sure it is made of something that won't scratch the interior of the cylinder and the piston) through the spark plug hole. You don't have to get every last drop. What is left should not prevent you from starting the engine - it will just belch gobs of white/blue smoke for a few seconds after it kicks over as the remaining oil burns off. Keep in mind that squirting a half an ounce or so of engine oil into the cylinder is recommended when winterizing to protect the cylinder from rust so it should not be a problem. In fact, I would expect that pulling the starter a few times will clear most of it in any case. It is possible that you have other problems - hopefully you didn't turn it over carburetor side down!. (In this case, the air filter may need to be removed and cleaned or replaced.) It may even be that your initial attempts to start it with an oil in the cylinder have resulted in a flooded the engine (excess gas) and waiting will clear that as well. Some of the following information may be model specific but most applies to any engine that has gotten oil in the cylinder and/or carburetor due to tipping: (From: J. Matthew Good (jmg14213@ix.netcom.com)). First, my guess is that it is a Briggs QUANTUM or SIGNATURE SERIES engine, with the paper air filter. Go buy a new filter, as that one full of oil is shot. Next, remove the plug and secure the plug wire away from the opening. Crank the engine a few times to clear the liquids out of the cylinder. Reinstall the plug. Now take a 1/2 inch box wrench and loosen (don't remove) the plug/nut on the bottom of the carburetor until gas flows clear through it, and retighten it. This should get the oil out of the carburetor. Now, check the oil. Since you lost so much into the carb, and air filter, and it only holds 2 and 1/2 cups total you will probably need to add oil. If not, you may have gas in the oil as well. Drain the oil into a pan for recycling by tipping the mower air filter up, and dipstick tube down. Fill with clean SAE 30 HD oil. DO NOT use 5W30, 10W30, 10W40, or any other W oil. Just SAE 30 HD from any discount store will be fine. Do NOT use SAE 30 ND, it does not have the needed detergents. Now you have the liquid out of the cylinder, the oil out of the carb, the gas out of the oil, the air filter OFF, and you are ready to start the engine. If it has a CHOKE, set it for full choke, if a primer, press it 3 times. Pull the rope until it starts. Let it JUST RUN until the smoke clears, don't mow or anything else until the smoke clears and you reinstall the NEW air filter. The reason I guessed it was a Quantum is that this is the only engine I know of that automatically puts oil in the air filter if you tip it for sharpening. That's why the first thing I do to any Quantum that comes in for service is remove the air filter and put it in a safe place. (From: Lloyd E. Sponenburgh (lloyds@fiscalinfo.com)). Actually, a judicious tilt *away* from the carb will coat the underskirts of the cylinder and piston with oil so as to make starting *easier*. This improves compression. It's an old salesman's trick to show just how easy it is to start the engine.
Not everyone agrees with the recommendation to drain the fuel at the end of the season as described in the section: "General preventive maintenance". (From: Dwayne (Dwayne@mddc.com)). There is some argument that draining all the fuel from the system is bad, allowing the carb to dry out and the inside of the fuel tank to rust. That was the case on my motorcycle; the guy who had it always drained the fuel for storage and it ruined the tank. I always just add fuel stabilizer to the tank, fill it completely, and run it for a short time and have never had problems. (From: Matt Howell (howell@ll.mit.edu)). Fuel stabilizer's purpose is to prevent souring, and hence, the need to drain the fuel system before storage. In my experience, my equipment starts right up each season with stabilizer in the fuel. I would suggest you clean/rebuild the carburetor. Repair kits are cheap, and easy. Good luck! (Editor's comments). I have cleaned and rebuilt too many Tecumseh carburetors (mostly from neglected Craftsman lawn mowers). The cause in most of these was almost certainly gasoline left in the fuel tank between mowing seasons. You might get away with it for a couple of years but eventually the goop will prevail. I would definitely recommend draining the gas with these. The fuel tanks are plastic in any case and there are only a few steel parts in the carburetor and rusting of these is not that likely. A fuel stabilizer may not prevent the buildup of gunk and varnish as a result of the slow but inevitable process of fuel evaporation in the carburetor and replenishment from the fuel tank. For other types, I would still recommend draining the fuel tank and running the engine until the carburetor is dry. I believe that this will result in the best long term reliability in most cases. Now, if you live in a swamp and mow the seaweed.... :-)
A used mower at a bargain price may not turn out to be such a bargain if you have to do extensive repairs. There are two types: the living and the dead. If the owner claims the mower will start and is prepared to demonstrate, this is usually a good sign! However, first, take a moment to check the following: (Disconnect the spark plug wire, and tie it safely away from the spark plug terminal to prevent accidental starting if you are doing anything more than looking.) * Check for significant oil leaks particularly around the main bearing at the blade/PTO end. This could indicate a defective oil seal or extremely worn main bearing. * Check the oil both for level and condition. If the oil level is low and/or really black and icky, the owner probably did not follow the recommendations in this document! The oil should also not smell of gasoline. CAUTION: the oil will be hot if you check it after the engine has been running for more than a couple of minutes. If there is gasoline in the fuel tank and it will start without undo effort, then there is an excellent chance that the engine is in good condition. * How much effort does it take to start? If 10 pulls on the starter cord are needed, this probably means that some maintenance, at the very least, will be required. * Check for unusual vibration and noise which could indicate an unbalanced, bent, or broken part. The blade of a rotary mower can be replaced easily and inexpensively if it is bent but any internal problems will be costly or time consuming to remedy. * Check for any unusual unevenness, surging, or sputtering. If there is more than one speed, see how smoothly the engine switches between speeds. Put it under load if possible (offer to mow some foot tall weeds) to see how well the engine deals with actual conditions that will be encountered during normal use. Problems here usually indicate at most that the engine needs some long overdue maintenance but it might help your bargaining position. In most cases, if the engine starts reasonably easily, there will be no really serious problems. The ignition system may require a tune-up or the carburetor may need cleaning and/or adjustment. Even a hard-to-start mower may very likely restored to tip-top shape with this type of intermediate level maintenance. Of course, the blade may have to be sharpened or replaced. If the engine doesn't work - no gas in the fuel tank and no handy gas can is usually a tip off of this - how can you be fairly sure that there are no major mechanical problems? Note that the objective here is not to identify **the** problem but to have a good idea of whether repairs will be really expensive or difficult. Thus, we won't even bother checking the carburetor or spark as problems in these areas are minor compared to those caused by internal mechanical damage. Here are some simple tests you can do without tools and without overly upsetting the people running the sale or junk yard: WARNING: disconnect the spark plug wire and tie it safely away from the spark plug terminal if you will be doing anything under the deck. Yes, I know, there is nothing in the fuel tank but it doesn't hurt to be safe. Use a rag or proper work gloves if you attempt to rotate the blade directly. * The single most important test is to determine if the pull starter will rotate the engine without binding or unusual noises. If it doesn't turn at all or with great difficulty - and there isn't a clump of grass stuck between the blade and housing, there may be severe internal damage including broken parts or seized bearings. However, make sure that the blade brake is disengaging before walking away - it could be that simple (you did remember to grab the dead-man bar or set the throttle control to RUN, right?). There is also a very slight possibility that the starter itself is simply tangled or rusted and that the engine itself is fine. In this case, you should be able to rotate the blade and it should rotate the crankshaft. * For a 4 stroke engine, you should feel the resistance of compression once every two rotations of the crankshaft (blade). If there is a tough spot every rotation, the valves are not working probably due to broken teeth on the crankshaft gear or camgear. (For a two stroke engine, there should be compression on every rotation.) * If it turns too easily with minimal resistance (and the blade is actually rotating, not just the starter) - you should have an idea of the effects of proper compression on a typical mower - then there may be stuck valves, worn piston rings, or other internal mechanical damage. * If possible, perform this simple compression test: Spin the crankshaft is the opposite direction from normal. A sharp rebound on the compression stroke indicates decent and probably acceptable compression. Little or no rebound means that the compression is probably low. (This is actually the only compression test Briggs & Stratton recommends.) * If the cord pulls out with no resistance and doesn't rotate the blade, the starting clutch may just be broken - a very minor repair. Then, you will have to check for binding by rotating the blade itself (carefully). * If you found the starter cord broken, this could be minor and simply due to wear or forgetting to engage the safety bar once too often - or major resulting from attempting to start a broken and seized mower. I picked a mower off the curb once where the cord was broken due to guess what - a clump of grass stuck between the blade and deck. Apparently, the cord was quite worn and the mower stalled on the clump of grass. The next yank likely resulted in a stream of 4 letter expletives and the mower was put out in the trash. Extracting the grass clump and replacing the cord yielded a rear bagger in perfect operating condition. Another mower found in the trash was not as fortunate requiring the replacement of the gear on the crankshaft and the camshaft/camgear assembly due to broken gear teeth ($35 - it was a learning experience), carburetor overhaul, and a tune-up. Assuming the engine doesn't flunk any of these tests, then you may end up with a functioning mower with relatively little additional cost and effort.
"I am in the process of refurbishing an old Eska 7.5 H.P. outboard boat motor. The engine (a 2-stroke Tecumseh) runs fine when under load at full throttle. I can only get the engine to idle at a high RPM. If I lower the idle speed, the engine will eventually die. Once the engine is started and idling, any attempt to put it into gear will cause the engine to die. Sometimes it will stay running and I can get the throttle revved up at which point the motor will push the boat and run just fine. When I lower the engine speed (approaching the dock) the motor will eventually die. I am totally stumped. I've completely rebuilt the carburetor (new seals, etc.), replaced the condenser, points, and spark plug. I've set all adjustments to factory specs yet it still won't idle or go into gear." (From: Al Savage (asavage@iname.com)). Although I haven't worked in the field in 15 years, two stroke theory doesn't change much. Is your high idle (out of gear, unloaded) smooth? It shouldn't be. Two strokes without electronic mixture controls are almost always calibrated to be slightly rich when unloaded, as the nature of all three induction systems (piston port, reed, rotary valve) is such that adding a load leans the effective mixture. Something to do with flow dynamics, I didn't need to know, as I don't design them. You've covered the common problem area -- ignition. I suspect you have an air leak somewhere. Upper or lower crankshaft seal, reed plate gasket, intake gasket, and upper housing gasket are common areas, in that order. Mind, this is generic two cycle troubleshooting advice; I don't pretend to know the model you're working with. To track these things down in the shop, we'd build custom block off plates and pressurize the crankcase to a few inches, then watch the gauge to see the leakage rate. Not terribly practical unless you're rebuilding, but you sometimes found porous castings and cracks that way. When I'm feeling adventurous I'd spray starting fluid (with a tube nozzle attached) around all the seams with the engine running to see if the run behavior changed. Not recommended; too dangerous.
(From: Mike Brandt (mwbran1@uswest.com)). A quite common problem with these engines is the gasket between the carburetor and engine. It is usually a thick fiber gasket and sometimes gets blown out if engine ever backfires. This is more common with age, as the nuts holding carb on do sometime get loosened. Also gum buildup can and does clog the main and low-speed jets at times which means removing carburetor. Cleaning out with a good carburetor cleaner then blowing out all passages. This happens quite often here where they add 10% alcohol to gasoline. Gas goes bad a lot quicker than without alcohol!
The following was in response to a posting on alt.home.repair about a 12 year old lawn mower. Of course, if properly maintained, such an engine may still have quite a bit of life left in it :-). (From: foxeye (foxeye@www.mindspring.com)). The best method is if you do not have a flywheel puller is take it to the nearest Briggs dealer and have them remove it. Since you do have a puller, just put some tension on the flywheel with the puller you already have, and then hit the top of the puller (the threaded shaft that centers on the crankshaft end) with a heavy hammer (16 to 24 oz.) should do it. Sometimes all it takes is a sharp blow with tension exerted on the flywheel to break it free. One or 2 raps should be enough. If it fails at that, there are still other ways to remove it. Some have points and condenser some do not. There is a points/condenser replacement kit that makes it solid state available for less than $10.00 called Atomic Ignition. Also rust on the magnet of the flywheel and the ignition coil laminated portion can also cause it to have no spark. The measurement is critical for the ignition coil to flywheel space (called air gap) for proper ignition as well. Unless very badly corroded and worn, the points can usually be cleaned up and readjusted. Its not uncommon for the little fiber plunger that operates the points on some models to get stuck. You should pick up a manual, for proper dimensions, and bolt torque. Even though it may list special tools for some repairs, there is usually a work-around in most cases. I would not really spend to much money on this motor, as the age is against it, but a new one from a source like Northern Hydraulics can be had for $99 to maybe 125.00. I picked up a 5hp highwheel lawn mower with a Briggs I/C motor at the end of last summer at a local builders supply and garden center for $130.00 new in the box.
(From: Dan Hicks (danhicks@millcomm.com)). Last Monday, while I was mowing the lawn, our 21-year-old Snapper mower quit on me. I could start it up but it would run for a few seconds and then quit again. After futzing with it in the yard for several minutes I took it back to the garage, and, after several more attempts at getting it going, I decided it was likely getting too much gas. I disassembled the carb and cleaned it good. It's a "PulsaJet" model with the carb mounted on the gas tank. The diaphragm looked good -- no visible holes. I reassembled things and the thing started and ran well enough to finish mowing, but it didn't have much "oomph". During the week I got a new diaphragm, and I got around to installing it today. What a difference!! It used to take several tries to start the mower, now it starts on one pull. And it has more power than it's had in years. Hard to say what may have been wrong with the diaphragm, but likely it had some microscopic holes in it.