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

3276 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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First, make sure the stick or a portion of it isn't lodged preventing rotation.

Riding mowers are more forgiving than push powers when hitting foreign objects because of the belt driven blade(s) but still the spark plug needs to be pulled and observe if the piston moves when it rotates that inch. Try rotating it backwards from the point where it stops.
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