woodruff key

[rednipj]

Took my raptor out this weekend rode for about an hour then it started running bad, stalled, wouldn't crank, it will turn over and let out a loud backfire.  Figured it was something with the valves.  Took a lot of it apart found the woodruff key on the flywheel to be the problem.  Sheared right off.  I'm getting the parts to replace this and was wondering what would cause this to shear, being that the only real resistance is the starter when it's ingaged other than that the flywheel is just spinning against nothing, correct?  Any advice will be appriciated now that I have it torn down and ordering parts, is there anything else I need to look into?

[450rcrazy]

somtimes happens when the engine is abruptly stalled or brought to a halt suddenly.the momentum of the flywheel itself will shear it,crank stops flywheel wants to keep spinning.or if the flywheel nut is loose the movement of the flywheel under acceleration and deceleration can slowly eat through it.Just a couple of possibilities .

[Yamaha72]

Very odd, but if you want a little added performance and since you already have it apart... Vito's Perfromance makes an advanced "woodruff" key. I had one in my blaster and it worked pretty well. 

[rednipj]

Makes sense, will be ordering parts today.  Woodruff key & 2 seals.  Just wanted to be sure it wasn't anything I was overlooking.  Thanks again,