Why does key shear off?

[Warriorfreak99]

Had my warrior shear two flywheel keys since I've had it and I was wondering what causes it?

 

[1998yamahawarrior]

I had mine do the same. I may be as simple as the flywheel isnt seated enough, or the spacer that goes thru the cover isnt getting the proper torque. Last time I replaced it I made sure both were good and Ive been good every since. Knock on wood!! LOL