Well, I was about to, but I could not find my wheel puller. However, I did do a visual
inspection from the top of the crank shaft and the slots in the shaft and the flywheel appeared to be in perfect alignment. The end of the key looks okay too.
One more piece of information. This is an old machine, as you can see. When my mowers get to a point where they are showiing their age, I assign them to mulching
leaves etc. in the woods behind my house. Occasionally I will hit a rock or a piece
of wood which may stop the machine. Once bent a shaft doing this, but generally
that does not happen. looking at the engine diagram, I'm also wondering if I may have
damaged the timing gear or the timing key. If all else fails, I'll do an autopsy on the
engine because I'm curious. Will share the results of the post-mortem with you if it comes to that. The only reason I'm trying to save this old machine is for its 6 HP
engine. One other thing I should have mentioned....... when starting the engine after
it has not been used for a while, it's quite "stiff" (ie the crankshaft does not turn as freely as it should). After running for several minutes the engine is quite loose....it's almost too
loose. Pointing to internal damage???
My wife say "junk it" but the engineer in me has to know what happend. Anyhow, I'm
electrical; not mechanical. Just took enough mechanical courses (theory) to be
Microphone to you Rick.
If the slots are lined up exactly then the key is probably okay. However, it doesn't take much. If there's even a ridge you can feel with your thumbnail that's enough to throw it off, and kickback is usually associated with a timing issue.
If there have been impacts, it's possible that the crank gear pressed onto the crankshaft may have spun slightly. An easy way to tell is to take the breather cover off the side of the engine and watch the action of the valves opening and closing. At top dead center on the compression stroke, both valves should be open, but at TDC on the exhaust stroke (180 deg. further on the cam shaft), both valves will open and close alternately as you come up to TDC and come back down.
It sounds like you may have some wear in the engine as well, based upon the stiffness and looseness you made comment to. when metal gets hot it expands and steel an aluminum expand at different rates.