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Will a sheared flywheel key cause a lawnmower engine not to spin?

3275 Views 8 Replies 5 Participants Last post by  de-nagorg
My riding lawnmower just broke while i was mowing leaves. I've rebuilt lawnmower engines before, and I'm fairly certain the piston rod broke, but i couldn't remember what the symptoms of a sheared flywheel are. Would a sheared flywheel key cause the engine not to rotate when you spin it by hand? It will move an inch or so and then stop like it's hitting something.

Like i said, i'm fairly certain something broke inside the engine and that it cant rotate because it is hitting the part... but wanted to check anyway to see if a flywheel key might do anything like this.

It shut down about 45 seconds after i hit a big stick or something with my blades, and i know that is what can shear a flywheel key... but it might have just been coincidence that it stopped shortly after hitting something... or that jolt might have caused the internal parts to fail.
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If the flywheel key is sheared, I would be looking into why it sheared.

As you think there are very few ways to shear them, unless the engine actually locked up, I cannot think of any other way.

So plan on a major rebuild of that engine.

Quoted from the above

i reused the old journal which had just a tiny tiny nick in it... so now i wonder if that might have contributed to this failure.

YES ABSOLUTELY, if not, it was a bad idea.

It's good that you learned some things from this experience, and saved money on those other engines.

Life is a journey of amassing knowledge, keep on learning as it keeps you out of trouble.

When you take it apart to see exactly what is broken, I would be interested to know also.

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