sheared flywheel woodruff key

[seitz729]

I'm a happy camper! I:II just got my project Blaster rebuilt and up and running today. After much frustration and head scratching, I took it over to a local indy shop to help get it started after my top end rebuild. They diagnosed it to be a sheared flywheel woodruff key. I've been trying to do some research into this (woodruff key) but I'm still unclear. Could anyone explain in layman's terms the function of this part and what might have caused this failure? I'm assuming that this was the reason the blaster was not running prior to my purchase. It had low compression and a very weak spark prior to my rebuild. thanks, Dave

 

[sicivicdude]

The woodruff key aligns the flywheel with the crankshaft. Because the triggering mechanism for the ignition system is based off a correctly timed flywheel, there is only a single way that it can be installed...

The key, contrary to popular belief, is not what KEEPS the flywheel timed correctly. The interference fit between the crankshaft taper and flywheel taper keeps the flywheel from spinning. If this is a reputable shop, they will "lap" the flywheel taper to the crankshaft taper to keep that problem from re-occuring.

 

[Blaaster]

/\ /\ /\ /\ Wot he said.

If the flywheel had been put on with the incorrect torque settings, it could have caused the flywheel to spin causing the key to shear.

 

[seitz729]

/\ /\ /\ /\ Wot he said.

If the flywheel had been put on with the incorrect torque settings, it could have caused the flywheel to spin causing the key to shear.

thanks for the reply and info. I will keep my fingers crossed.

Will I know immediately if this were to happen again in the future? What are the symptoms of a sheared key? Can you start or run a bike with a sheared woodruff key? I'm assuming that it will throw the timing off, but could this have caused my weak spark?