Mower Repair Questions

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. Replace deadspam with yahoo to reply.
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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.
NJBrad
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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.
KB
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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 blade
bent PTO crankshaft
damaged blade adapter.
If it runs and is vibrating check for bent blade & or crankshaft.

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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. . . . DanG

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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.

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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.
Pop

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Maybe a bent rod.
Tom

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wrote:

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 Replace deadspam with yahoo to reply.
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yes the timing only and have no effect on vibration. Bent crankshaft typically will cost you between 150.00 to 250.00 depending on parts cost & labour per hrs rates. at most shops.

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