woodruff key help !!!


Active Member
Local time
11:30 PM
Dec 15, 2006
Fountain Hills, AZ
i was riding with azvinnie and when I popped the clutch I heard a loud thunk
when we pedaled home, I found the drive sprocket had sheared the woodruff key :eek:
I guess when the key went it caused the sprocket to spin freely, taking out the threads between nut and crank :eek:

I have two questions
1. is it toast (no-repairable)?
2. any idea what would cause key to shear ?...I am fairly gentle with take-offs

I have access to another dax engine that the crank n head are gone , if I knew how to take the parts from it, I could use them in mine

if I am done...my next will be a 4cycle !!!
I have read horror stories about the Chinese studs/cap screws used on these motors. The woodruff keys might fall in that same class.
Keys should be fairly hard and tough. I bet the slot in the drive gear fit the key on the loose side and the nut was not tight enough permitting the sprocket to work/vibrate against the key.

If the threads can not be saved you might get by with bonding the drive sprocket on with liquid steel epoxy. For removal a pre-heat of 500F would brake the epoxy down.
Be sure a ask before doing this, as pre-cleaning is very important.

In your opening sentence you did say, "popped the clutch".
bro ,I dont know sounds like the key could have gone just from normale wear but the piston might be locked up also...can you replace the key and try to start it again...... if that one shears you going to have to do a tare down on the jug......let me know
ok, here's what I did to fix it
took woodruff key from baffed engine and put it in mine
put sprocket back on and put nut back on without lockwasher
(just to have a little thread for nut)
tightened as much as possible
went to local hotrod shop and got nut tig welded to the shaft...10$
I know it's permanent, but I didn't seem to have much choice
...and, it seems to work
The woodruff keys are designed to fail. I didn't think these little engines had enough power to cause one to break. Guess you won't have to worry about that anymore though.
i suspected there'd be a little welding in there sum'eres...there always is :LOL:
i'm bumping this...the question's come up again. i locked the duplicate question, but i don't want the OP to go without an answer.

let us know if this helps, & let us know (in this thread) if you need to know more :)
Is that a 3/16 size woodruff key ? does any hardware store have them ? I went to the motor bike shop and they don't have them