WR450F woodruffkey too tall?

My WR450F will hopefully arrive here in Austria this week, thus i asked the dealer if he has got any Service Bulletins regarding the woodruff key issue and whether he'll lap the flywheel to the crank or something.

He said there actually is a bulletin but it required him to order a special woodruff key (which he already did) and to replace the original key with that new one, plus use some loctite stuff on the key(!) when assembling it.

He definitely is not requested to lap anything!

Confronted with the "US experiences" and the rumored Yamaha US service bulletin (which i myself only have heard about here on TT) he suggsted that maybe actually the original key is slightly too tall thus preventing a good full surface contact between crank and flywheel!

Like as if the key's height slightly exceeds the sum of gap depth of the key's groove in the crank plus gap depth of the key's goove in the flywheel. This would be hardly noticeable, allow people to align the items correctly, tighten the nut to whatever torque they want and still prevent a good, full surface contact, thereby making the key a load bearding item which a woodruff key never is.


i'll post when i get stranded in the woods with a sheared key :)



Rowdy, I suggested and suspected this could have something to do with the lack of a proper interference fit quite awhile back. I will be most interested in finding out if Yamaha has indeed determined this to be a major contributing factor. There can be almost no other explanation for the lack of a good fit when some guys have checked the surface match of gear and shaft and found it good (w/o the key).

I suggested tightening the gear onto the shaft without the woodruff key and then seeing how much resistance there was to the gear being removed. It should require a puller at the least and preferably a little heat as well. If that checks out, then install the gear with the woodruff and recheck the resistance to removal. If there is a noticable difference, you have found the culprit: a woodruff key that sticks up too high and prevents a proper fit.

I don't know whether any 450 owners tried this or not...

I also pointed out that my experience with a similar setup on Polini clutches is that once a gear has spun on the shaft, it is far more likely to in the future no matter what is done short of replacing both shaft and gear. The repeat cases here tend to bear this out as well.

I am not trying to be Mr. Know-it-all here, but I swear this is exactly what my friends who are unfortunate enough to have purchased Polinis for their mini racers have been battling for years! Same setup, same problem, likely the same cause. This is further born out by the fact that Cobras also use a tapered shaft for their clutch but DO NOT have a woodruff key and their clutches almost never spin! If they do, it was simply a lack of proper torque. Don't forget to use red loctite on the shaft/gear mating surface and the nut!

This is a very interesting take on the possible causes of key failure. I did pull my rotor and lap about a .001 high spot and put in a new woodruf key. The key was ordered out of stock and may not be out of spec. Our weather has improved and I am riding dirt roads in the area and so far have not had a problem. Hope my fix will hold up to the rigors of offroad riding when our ride season begins next month.

Chaindrive, i know what you mean regarding damaged taper fit once the woodruff key fails:

Back in the ice age when we were young, stupid and innocent a buddy and i tortured an already worn out and not maintained Bultaco 370 Aplina. Eventually the woodruff key broke. We did make a replacement out of the support metal of the bumper of an old VW beetle (in europe every second farm house had some rusty beatle lying around).

Needless to say the metal was way too soft, and did break in no time. Then damage could not be fixed anmore as the taper of the crank had been scarred by the ripped key from rotating w/o the flywheel comming along. Damage way beyond lapping, case closed. (we were lacking all funds to buy new parts, back then)

Personally, i'll bug the dealer to let me see the bulletin, and maybe pull it all apart back home for a "better save than sorry" lap session, together with your suggested check of difference between key in and out.


Got off the phone with my riding buddy's yamaha workshop (sadly not allwoed to sell new bikes). He has got that Service Bulletin!

I'll simply help him with his computer quirks and get me a

photo copy of that bulletin. Check back here in a couple of hours.


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