Sheared flywheel key

1998 75hp Mercury

Keeps shearing the flywheel key.
Will start and run and then makes a noise and shears the key.
So far 4 keys.

What type of noise,backfire,spit,clank???????

Hydro racers cure that problem with grinding compound. Smear a bit on the mating surfaces and rotate the flywheel back and forth a few times. Then clean it thoroughly before installation; and use NO lubricants!

Jeff

The tapers are smooth.Clean and no lubes.
Clank,clunk.
Then a noise from the starter when it tries to turn the flywheel.
It has good compression.
No chunks or excessive pieces in the oil. New oil.

The magnets in the flywheel had came loose and he ended up taking them out.
Still starts just no charge.

If flywheel has no magnets ...how does it run????

I have a forty hP Johnson that is doing the same. My engine is sort of back firing (after running normal at start up ) and instantly changing direction with the backfire (more like a pop). I just can't work it out. Would the head gasket be leaking through into the next cylinder and firing it before TDC.? Does this sound like yours ?

That "wanker " Has helped Thousands on this site. The mods will tell you the same thing.
He did help YOU. He gave the best advice. Post in the right section with the right info, year and model.
They'll ask you to leave. Be nice.

Upon further inspection: The flywheels taper was bad.
New wheel $475 OUCH.

And no the head gasket probably wouldn't do what you described.
Do a compression test.
Check the reeds behind the carbs
Depending on the year and model the air screws might need adjusting.
I say year and model because not all OMC's had carbs that could be adjusted.