keep shearing flywheel keyway?

easy solution
Take off the fly wheel and key,and put some fine grinding paste in between them and work as if you are grinding in valves (but in a circular motion complete turns to enable the shaft and flywheel to grind itself into a perfect fit,clean and check until good fit re-assemble and lock tight.

cg
December 2010

Check that there is no difference in the position of the keyway with respect to the position of the magnet, between the 2 flywheels. If there is, that's your problem (now), but that doesn't explain why you had the ring gear problem in the first place.

Ensure that the flywheel nut is TIGHT (to B&S spec.). The key is only a locator - it isn't supposed to cope with crank torque. The taper should be sufficiently tight to prevent flywheel slippage. I have successfully assembled and run engines with NO KEY at all to demonstrate this to dis-believing students!

phil_saunders(a)bigfoot.com

Phil Saunders
November 2010