Size is everything

The woodruff Key!!! Since the WR is down with a sheared key (waiting on a new key) and I finished prepping the KTM for the Gerogia GNCC I was putting a new rod and crank bearings in #5 a 99 RM125 and as I was putting it together I notice it's key a massive .155 thick .253 deep and .515 long compared to the puny .119 thick .210 deep and .488 long wr key. I weighed the rotors RM125 1.2 pounds WR 2.6 pounds. Now I ain't suggestin' nothin' but........

Is that what she said ? :)



And it only a little 125 2 stroke?

makes you wonder.

The engineers will tell you the key is only used to position the rotor/flywheel, not to hold it in place.

So why is the key on the 125 so big?

Yah see, it takes special people with especially small fingers to put the key into place and slap a flywheel on at the assembly line so therefore since specially qualified persons were needed, they had find these people, that takes time, then you need to make sure that these especially small fingered people could do the work fast enough to keep up with the assembly line pace, that also takes time.

Does everybody remember the dates we were told that we would get these great bikes with tiny woodruff keys? Now considering the special circumstances I have outline, I think we have found our reason for the delay in getting the WR's to us!

So the morale of the story is design big woodruff keys so that you are not running late getting the product to the customer!


Well you may not be suggesting anything but here is my opening to suggest. When I pulled my flywheel to lap it I was amazed at how small the key was. This was based on previous motorcycles I have had. Let's say Yam under torqued some bikes, and some have rotor surfaces that don't match well, and some have both conditions.

If some forces are applied such as backfire, locking up the bike, or whatever, the forces are twofold, first spinning the rotor (opps the key broke) or the rotor moves slightly away from the shaft and no longer has sufficient purchase,and then the rotor slips (oops there goes a key.) I contend, but have been afraid to say it, that the key does have some responsibilities other than timing alignment. Those responsibilities are to shoulder a slight movement of the rotor that was torqued correctly but still might move a few thousands of and inch and then provide enough support that the rotor holds in place. This key is used on the 426's and the YZ and Wr 450's. I wonder which rotor weighs the most (450?). I don't think the key is up to the task. So, how about a longer one, that will give it greater shear strength. Others have said it is the job of the key to shear intentionally to save the engine from some disaster. Someone explain why it needs to do this.

IceBox ,

LOL thats funny. :)

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