Flywheel Key Shearing

[fritz1255]

I have a Model 850 Briggs & Stratton single cylinder engine (190 cc I believe) that keeps shearing the flywheel key for no apparent reason. Is it possible that I am not tightening the flywheel nut enough, and it's working itself loose somehow? I haven't used a torque wrench on it yet.

 

[Rivets]

Should be torque to 65 ft. lb. Bet you are right that it is not tight enough.

 

[bertsmobile1]

You might need to dress the flywheel & crank if you have busted a few keys.
Tapers work by being a very close fit so if there is a lip or welt on the edge of the key shafts it prevents the tapers from locking together no matter how tight you do up the nut
Put a tiny smear of grease under the nut, not on the threads to allow it to turn easier on the bearing surface and clamp the flywheel without turning it & breaking the key again.

 

[tom3]

Might sand the taper on the crank and the inner bore of the flywheel with some fine grade paper, get a better contact fit.

 

[bertsmobile1]

Might sand the taper on the crank and the inner bore of the flywheel with some fine grade paper, get a better contact fit.

Should lap them together with extra fine valve grinding paste ,or Brasso if you just need to knock the polish off the surface.
Like doing a valve you turn it back & forth , lift, rotate 1/4 turn and do the same .
make sure you protect the top oil seal put some vasoline around it then wash off with hot water.

 

[tom3]

Have to file that away here, good info. Thanks!