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.
|NotTaR of small Gasoline Engines and Rotary Lawn Mowers : Testing a used lawn mower before you buy
1994-2007, Samuel M. Goldwasser. All Rights Reserved. Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied: 1. This notice is included in its entirety at the beginning. 2. There is no charge except to cover the costs of copying.
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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
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
- 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
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.
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