Flywheel keys

[RoostDaddy]

A buddy of mine has sheared 2 flywheel keys within the last 2 months on his K5.  I told him to clean the pieces out of the flywheel and off the crank.  Then use a piece of emory cloth (lightly) just to make sure everythings smooth.  A dab of valve grinding compound and mate the flywheel and crank.
 
If this continues does anyone have a better suggestion? 
And what would cause it to shear the keys?  My thought was too much timing, but it was set @ stock.

[KXcam22]

Roostdaddy,
Timing should not have any effect on the key unless it backfires hugely. From what I understand, that is caused by a poor fit between the flywheel and the crank tip.  Your solution of using the valve grinding paste is the correct one.  I did that on mine (no previous issues) and was suprised at how much lapping it took to get an even wear pattern.  It's nice that with lapping the flywheel it does most of the work.  Clean it up, lap it well and torque with blue loctite.  Is there any chance he has the wrong key?  You can also put loctite on the shaft for additional hold. Cam.

[demographic]

I lapped mine in with valve grinding paste (although I had no problems before that) as a precationary measure.

Was so  easy that I will do it on my other one as well.

[DoldGuy]

Good info by Cam, make sure it is torqued down correctly. Recently I have seen & heard about this even on the 250's running a flywheel weight. Is he running a weight on his? Makes me also wonder where these keys are being made & out of what?

[alward25]

If you don't buy OEM keys you will most likely have problems. If the the keys are a hair too tall they will crack when you torque the flywheel down and fail.
Lapping the Crank to flywheel is a great recommendation as previously mentioned.

[RoostDaddy]

Right key, no flywheel weight. 
Maybe the first time it just wasnt lapped enough.  Hopefully it is this time.
I just wasnt too sure if there was something else other than them not being mated together.  But this seems to be the verdict by all.
Thanks for the input!

[kaw rider]

recommend new nut thats not gail up and torque down to manual spec.

[Polar-Bus]

A buddy of mine has sheared 2 flywheel keys within the last 2 months on his K5.  I told him to clean the pieces out of the flywheel and off the crank.  Then use a piece of emory cloth (lightly) just to make sure everythings smooth.  A dab of valve grinding compound and mate the flywheel and crank.
 
If this continues does anyone have a better suggestion? 
And what would cause it to shear the keys?  My thought was too much timing, but it was set @ stock.

I work a lot with tapered fits and keyways on industrial fluid pump shafts, and I can share what i've learned. If you have experienced a sheared key, that means that counter-rotational forces from the flywheel was hammering the key, which in turn was hammering the primary output crank taper keyway slot. My thinking is that there is a slightly "raised" area parallel to the slot on the crank taper, and this is causing the flywheel to have a less that ideal fit. I would try to carefully file down the area all around the keyway slot. Also make sure the key has a clean, and snug fit within the crank keyway. It's hard to pinpoint this issue without actually running a dial indicator around the area of the keyway, but it's a thought... good luck, hope you get it squared away!

[hughes]

Crank tapers and the flywheel inner hub is an interference fit. It's mechanically locking tapers. The flywheel key is just a locator for the flywheel. The flywheel nut when torque presses the two tapers together. It's very important that the inner hub of the flywheel and the crank tapers are cleaned with contact cleaner before install. Once the flywheel is installed correctly you could remove the flywheel nut and run the bike with no issues (not recommended).