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timing,it is made of aluminum metal, which allows it to
shear instead of crankshaft breaking when engine
backfires or in the case of a pushmower the blade comes
into contact with something that causes the engine to shut
down.
When a flywheel key shears or is pinched, it puts the
engine out of time, so that it will not crank or if it does it will
not run smooth.A pushmower or pullrope type started
small engine will kickback so to speak and actually snatch
pull rope from your hand.This is a common problem on a
lot of mowers, when someone hits something that shuts
engine down.
Bigger small engines will also shear, especially when
engine is allowed to backfire, for instance, rising up on
your riding mower seat and setting down before engine
stops, some engines will backfire and cause the key to
pinch or shear.
To replace the flywheel cap has to be removed,usually
there is a nut that hold the flywheel to the crankshaft or
starter clutch on some pushmowers, once this nut and
washer is removed the key and keyway will be visible, you
usually can see if its sheared ,because key and keyway
will not be aligned if sheared.The flywheel must be pulled
to change key,you can use a gear puller and if a 11hp or
larger engine,you most definitely will have to use a gear or
wheel puller.A 3hp to a 5hp you can use a shade tree
technique of rotating flywheel around to where you can
strike flywheel with a rubber mallet directly accross from
flywheel key while prizing underneath flywheel, or
replacing the flywheel nut down even with the top of the
crankshaft threads, not all the way down,and strike the nut
with the mallet with the prize under the flywheel,usually
after several stikes the flywheel will pop up, if not the the
wheel puller would have to be used.
Briggs small engines use one type of flywheel key for
most all of their engines, from 3 hp to 18 hp,whereas
tecumseh has four or five different keys for their different
engines, why I DONT KNOW. If your engine is getting fire
fuel and air and is not overhead valve engine, check the
flywheel key if it wont crank.Check out our parts section.
We will continue to add to it as time goes on, from tools to
parts.Hope this snippet of info was useful,it is a common
problem on small engines.