Rotor lapped and torqued still shears key

Well :D :D :D :D :D :D :D :D :D :D ;):):p we lapped and torqued the rotor to 47ft lbs. First outing the key sheared. It happened when slowing hard for a turn then it just quit, hit the starter button and it just spun luckily that we were close to the truck, got it home and the rotor nut was loose and the rotor would spin. My observation is that the rotor is awful heavy maybe too heavy. I guess we'll just wait putting in another key won't solve the problem. Gotta go cleanup the KTM 400 EXC for the second round of the GNCC in Georgia.

Did you locktight the nut? thats the onlything I can think of that maybe the nut loosend.

Ditto on the lock tight question and was your bike rejetted?

Yeah it was loctited I'm running 48/160 jets

Has anybody actually heard from Yamaha, (not some dealer but the corporation), to lapp the rotor?

I believe it is a mistake to lapp this assembly. I have seen the service manual supplement and there was no mention of lapping the rotor. The problem is the torque applied to the rotor nut.

"The problem is the torque applied to the rotor nut."

Yeah well yamaha corp. has listed 3 different torques 50 then 61 and finally 47. This was before anyone even took delivery! When I dykemed the crank there were severe high spots after trying the rotor. The only logical thing to do is to lap (one p) it. I don't need yamaha too "bless" something we've done for 35 years of racing. After looking futher at the rotor I think yamaha will find that it's too heavy (mass) for the taper and that's why it's shearing the key.

Well - now you can JB weld the rotor on.


sounds like you did everything you could. Still broke. That SUCKS. I wonder how much the WR rotor weighs compared to the KTMs?

Wouldn't there be a lot more failures if the problem was an overweight flywheel, like every bike? Maybe the taper in some flywheels isn't the right hardness - you could check against an 02 flywheel taper with a hardness tester - or it could be that some flywheels were overmachined preventing a tight taper fit. But without comparing part-to-part to a bike with no problems it will be difficult to isolate the real culprit. It might be a good thing to post a request for anyone that had the key shear to log in and give their bike id number. Maybe the problem can be narrowed to a particular production run range - and if so, it would aid in identifying the problem and the fix by Yamaha - and in peace of mind for those who have bikes that aren't in the range. Have their been any problems encountered with non-american bikes, for example?

Dutch I sure hope the snow melts soon so you can get out, sounds like cabin fever. JB weld thats funny you still use that?

Adam I will weigh them this week.


something is causing the woodruff key to shear. What??? Nobody is 100% sure. There's a few things that haven't fixed the problem:-- Re-torque rotor nut to 47lbs.--Lap and check taper--Jet to 160m,48p,72s or whatever--Oh, and don't touch the throttle while starting???LOL.

I'm not saying the rotor is too heavy. But I'm not saying it's not. I'm not an engineer or mechanic. What do I know??? :)

That has much to do with my attitude Wrench, it's a long winter. This problem with the key has nothing to do with my personal ride, (BRP). I do frequently ride with a pal who has a WR450 and I always carry a tow strap :). He has been known to pray at the alter of JB Weld, that remark was meant for him. Your problem with the flywheel is unfortunate

and I am sure Yamaha will make it good for you.

If you ever get the urge to sample the Northern Michigan woods give a yell, we will show you our super secret Scuba Steve world famous single line trail.

HEY!!! don't be telling people about the secret trail. :D

JB Weld is awesome. You know it's one of the most important inventions of the 20th century. Oh ya,You know it.. :) It probubly WOULD fix the woodruff key problem. Permanently. LOL. :D

It has been posted that Yamaha sent techs to a few shops to do something to the WR450's, but what we don't know. So Yamaha has some idea of whats going on. It would be interesting to know how the bikes that had a Tech work his magic are doing????

Secret trail ????????? what secret trail ???????????????

is that up by wolverine ?????????????????????????????????

indian river ?????????????????????????????????????????

hmmmmmmmmmmmmmmmmmmmmmm. :)


Bottom line is that all engines backfire sooner or later so jetting cannot be a solution - only a means to reduce the likelihood. And I know that most people do not enjoy riding a time bomb, it would drive me nuts to ride alone with a situation like that. I'm just suggesting that a methodical approach that includes listing bike id numbers could help isolate the problem if it is limited to "some" of the bikes delivered to the US - and it could help yamaha determine what bikes need a recall for those that may have not yet failed. Comparing failed parts (assume a flywheel, for example) to good ones is a simple and time proven troubleshooting technique - and yamaha has the means to do that. If, for example, it turns out to be a flywheel problem, they will know what flywheel production run matches the range of the affected bike ID's. More of a proactive approach I guess - you know the dealers aren't (can't) going to do the work - this forum is an ideal starting point. Just a suggestion.

our super secret Scuba Steve world famous single line trail

XR 600, We will show you. Wolverine/Indian river is OK, but we can show you better! ---Mike


It sounds like you tried valiantly. That really sucks to hear it still has a problem. I do have a question about the key itself. After lapping for a good contact fit between the rotor and the shaft, you had to install a new key. Is it possible that the key sticks up a hair too far and prevents a full-contact interference fit?

You might try torquing the gear to the shaft without the key. (Don't run it, of course). Just see how much force it then takes to remove it. It should take a lot. Maybe even some heat. If it doesn't, you still don't have a good fit. If it does take serious puller force/heat to remove, repeat with the key installed and compare how hard it is to remove the gear then. If it is any less, the key is preventing a good fit.

If that were the case, a little filing down of the top flat portion of the key might help. The key should just index the gear, not support any shear force. I always put a drop of red loctite on the shaft to gear mating surface as well as the nut on our similarly designed auto-clutches.

Having done all of these things; I would be at a frustrated loss and probably be tempted to reach for the mig gun... or, more likely, be parking it back at my dealer's...

Good luck! What Yamaha does from here is going to determine a lot of future sales, and I hope they realize that.

super secret scuba steve single line trail... &%$#@! ??????

ive been riding in northern michigan since i was 12 , and ive never heard of it.

whoaaaaaa is me....i'm so unworthy. :)

Who said anything about Indian River/Wolverine??? And just because Mike Lafferty rides there doesn't mean it's the greatest. :):D :DWhat does he know? He rides a KTM...LOL

Wonder if he has ever sheared a woodruff key???

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now