I have a 21 inch Troy-Bilt self-propelled mower, about 2 years old.
While mowing recently the blade hit a hidden tree stump and the mower
stopped instantly. It restarted okay but now has a noticeable
vibration. Is it likely that the blade assembly or blade adapter has
been damaged, or is it more likely that the engine has suffered
internal damage? I have removed the blade and the adapter, but can't
see any obvious sign of damage. Is it possible that just re-assembling
these parts will result in a "fix"? Is it worth a try? Also -- is it
okay to start the engine without the blade in place, (and would this
answer my question about damage), or does the blade act as a needed
flywheel? Thanks for any comments or advice.
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The mower probably will not start without the blade. Make sure that the
blade adapter isn't damaged. (It's the part that has arms that wrap over
the side of the blade and sits above it on the shaft. Also, as hard as it
may be to believe, the flywheel pin on the TOP of the engine may be bent
and need to be replaced.
If that doesn't fix it, then you probably do have internal damage.
Like NJBrad said, it probably bent the "key" on the crankshaft. THe
key it there for just that reason, it will bend (or break) before the
crankshaft does. Don't operate your machine till you get it checked
out. A wobbling shaft, for whatever reason could be dangerous.
the key (flywheel key is not there to prevent damage to crankshaft. It is
made to save the flywheel only.
When you hit the stump you have 1 or more of the following damage
sheered flywheel key
bent PTO crankshaft
damaged blade adapter.
If it runs and is vibrating check for bent blade & or crankshaft.
I am surprised that it would restart. It should have sheered off
the Woodruf key which sets the timing for the motor.
The vibration can be from a bent blade, out-of-balance blade, or a
bent crankshaft. Crankshafts can be straightened, but it would
probably be more cost effective to replace the engine if this is
the case, unless you are able to disassemble the engine yourself.
If you want, you could balance the blade you do have. You should
be able to set it on a flat surface and see if one end or the
other is noticeably bent - if so, replace. Set its center point
on a knife edge, the heavy end will fall - grind the heavy end
till it balances. Reassemble and try.
I would buy a fresh blade and try it.. . least expensive. If it
was not knocked out of time (apparently true) you may luck out.
Running the engine without a blade will probably not cause enough
vibration to know. It will not hurt the mower.
Keep the whole world singing. . . .
Crankshafts once bent are done, do not straighten it , straightening the
crankshaft will only weaken it more then it already has been when first
bent. It is unsafe and the risk of it breaking off will increases.
Since you hit a tree stump as opposed to a rock, it's likely
the damage is to the blade itself; it either bent up/down
and/or back. If you can 't figuire a way to check the
blade's balance, try buying a new one; they're cheap.
If it still vibrates with a known balanced blade, then you
have farter to look, and it might be internal, or, more
likely, in the shaft the blade mounts onto.
Thanks to all of you for trying to help me. Apparently the problem is
something other than the blade (since installing a new one did not
reduce the vibration. I'm not very confident that I could analyze it
further or "fix" it myself -- even with the help of all of you. The
thought of doing surgery on the engine scares me a bit -- unless it's
real MINOR surgery. Maybe I should bite the bullet and just replace
the mower -- or get a repair estimate. Any thoughts? BTW, if the
problem involves a bent or damaged key, wouldn't that just affect the
engine timing as opposed to causing a vibration? TIA
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