We have a rear bagger mulching push mower. I accidentally ran over a
very thick tree route and it literally knocked the blade right off. I
was able to put the blade back on and when I manually turn it it
freely spins around but when I try to start the mower it won't start,
it makes a loud clunking sound and the pull rope sometimes only comes
out about half way and abruptly stops. Anyone have any conjecture as
to the nature of the repair and whether it would be less costly to
just get a new mower for a couple hundred bucks?
It seems very likely that you broke the "shear pin" that holds the flywheel
to the crankshaft and keeps it in place. You need a puller to remove the
flywheel. Don't pound on it with a hammer or you might break it or damage
the magnet. Once you get the flywheel off you may find, as someone else
pointed out, that it has other damage too. New shear pins are usually
available at hardware stores in the lawn mower parts section.
agreed, this is a common failure with Tecumseh engines. I had a handful
of Tecumseh flywheel keys on a shelf in my garage when I lived in
Michigan. My neighbor/landlord was always bringing his mower over for
me to fix and it was always the same failure, I guess they were hard on
mowers/never picked up all the rocks in their yard/mowed right over
roots and stumps. Inevitably it was the flywheel key (a soft metal key
on those, not a pin) the reason it won't start is because the trigger
for the ignition is on the flywheel, once the flywheel spins on the
crank the engine is out of time. Starts running bad the first time you
hit something and if you hit another something it'll knock it so far out
that it won't start anymore... symptoms exactly like the OP's. Kicks
back when you start, etc. (because the timing is too far advanced for
the engine to run)
The fact that I could "fix" lawnmowers and was able to repair a busted
window and "restore" (really just strip off years of sloppy painting and
re-clear) the old brass door hardware got me loads of brownie points. I
think I also tarred the cracks in the sidewalk so the weeds wouldn't
grow up through, edged the walk, weeded the flower beds (actually I
usually just threw my grass clippings in them and then only pulled up
the weeds that managed to get through all that,) and did a couple other
little things and my landlord was just blown away. Makes you wonder
what the average tenant was like...?
replace "roosters" with "cox" to reply.
The only way to be sure is to look at it, since I can't, I'll offer a
After putting the blade back on, tie down the auto stop and remove the
spark plug (so it doesn't start) and turn the blade around. Does it
wobble? Is the blade bent? Is the crank bent? If everything looks
straight and true, then pull the flywheel cover off and spin it
aroound to see if it wobbles or the crank wobbles.
If the crank is wobbling, throw it in the trash. If the crank doesn't
wobble, remove the blade and the flywheel and turn it to make sure it
isn't the crank and the "sounds" you hear aren't coming from the blade
or flywheel. If you still hear sounds, you more than likely have
serious problems. Trash it.
Thank you all for your responses. I did leave out one detail but have
no idea if it's relevant or would change anyone's opinion. At one
point when I was trying to start the mower, I realized I had
forgotten to connect the spark plug. When the spark plug isn't
attached, the pull rope operates fine. As soon as the spark plug is
connected, the pull rope acts up and the clanking sound starts
Sounds like the shear pin, and the timing is off. Pull the plug out to
examine if the piston is moving through the four strokes. (have a
The rope will jerk your arm back when the timing is off and the plug
Does the noise exist when the plug is out and you yank the cord 5
btw, I've never seen a mower blade "knocked" off.
He doesn't need a compression tester for a lawn mower that was working
well a little while ago.
Since it's a one cylinder engine, you don't need to disable the other
cylinders, so just take out the one spark plug and put your thumb over
the hole. If you feel pressure pushing your thumb off every so often,
you have compression. That is, at least one valve is opening (but
probably both) and then they are both closing, and the piston is
moving up in the cylinder. If you have any compression, I'm sure you
have adequate compression, give that you hit a route, or root. :)
I would check the gizmo that stops the engine when you release the
handle. See if that's stopping the engine from turning. If so, it's
fixable. If not, start shopping.
Oh yeah, I always follow engine repair tips from guys who call key parts
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