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

Old 12-05-15, 01:58 PM
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Will a sheared flywheel key cause a lawnmower engine not to spin?

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.
Old 12-05-15, 02:54 PM
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No, if the key shears it just means the flywheel isn't centered on the keyway any longer... it's spun. Probably the rod broke and the flywheel can only go so far.
Old 12-05-15, 04:48 PM
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That must have been a hard hit to break a rod. It's not common for key to shear on a riding mower.

Check under the engine and see if your belt pulley is not jamming on something. If something like the belt is wrapped around the pulley it will act like the engine is locked up. Hope this helps ~!~!

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