Sheared keyway on Briggs

[Pacerman]

Please help Any ideas.. Have 21 HP single cylinder briggs keeps shearing keyway installed on Deere 126 mower with 125 hours. Have replaced key way hardened key runs fine for short period. Alum key shears quickly. Please share ideas where do I check. Has any one had problems with this engine?
Thanks for all replys!!!!
 

[504]

Are you missing the special washer, or have it upside down on the flywheel. Put it the right key or you will destroy the crankshaft or the flywheel. Be sure to torque the nut too.
 

[RPM1941]

B & S engines use the soft key only for the timing, the taper drives the flywheel, must be torgued with impact tool, hard to achieve without.
 

[joe csuti]

Also check/remove any galled alum buildup from flywheel keys on crank & flywheel tapers,alum will prevent flywheel from sitting straight on crank taper & flywheel will not goto bottom of taper when flywheel nut tightend,causeing key to shear in a short time.
 

[rustyj14]

Be of the utmost care when tightening the nut that holds the flywheel on. You could shear off the threaded end of the crank-shaft, which would require a new craank-shaft! Best to tighten it by hand--forget the air or electric impact wrench!! BT/ST
Steel keys are not recommended in that application. Better check for what is causing the problems. rj