08 KX450 SHEARED FLYWHEEL KEY

[ThrottleJunky]

I stalled my bike in a turn and couldn't get it restarted.  I thought I flooded it while trying.  Took it home and tried to start it again but couldn't get it to fire off. Checked all vital signs and found the timing off a small amount. Timing kept moving so removed the flywheel and found the woodruff key sheared.

Anybody ever heard of the 450's shearing keys and why?

Thanks!
TJ

[Friar-Tuck]

  TJ,
 Although I haven't spent a whole lot of time with newer 4 strokes, the 500's have a reputation for snapping them.
  Why they snap may have to do with the fit of the tapers of the flywheel and crank.
The only remedy I read about was to lap the two mating surfaces.
   I used valve lapping compound and lapped the flywheel to the crank.  I didn't get crazy, maybe 5 min.  Turn by hand back and forth.  The idea is to get the High/low spots out.   Clean  everything well before reinstalling.
  Tuck\o/

[jonny500]

+ 1 this works well, listen to tucko he know his stuff

[ThrottleJunky]

Thanks for the info!

I did a light prussian blue check to be sure the taper contact was good before installation. I read about 90%. I will put a light lap on it before reassembly.

I haven't sheared a key in a flywheel since the early 70's!  I had about 15 total minutes on this engine.

Back when I was building this bike a 9 oz. Stealthy flywheel weight popped up on Ebay and I couldn't resist.  I'm thinking about the effect of the extra weights' inertia has upon stalling the engine. This may have something to do with it. 

I ordered 3 keys so if it happens again with the flywheel weight, it will be coming off!