Preliminary data on woodruff key failures


I am glad we agree! It is a production or design defect...... Yamaha seems to be on it on the West Coast. They need to share what they have learned. Their silence is deafening....

Well :D :D :D :D :):D :mad: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 luckely 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.

Would Locktite help this??

Not waiting to push, tow or abandon my WR450 somewhere in the CO/UT desert, I had the dealer replace the woodruff key and locktite a new nut to 47 pounds torque. As I watched the technician do these things he retourqued the nut twice, once remarking that the 47 pounds of torque "doesn't seem like it is enough". Iv'e since put 80 hard miles on the bike, but it still has me spooked. I turned down a Moab White Rim ride next week and I'm going to place the bike on the stand and wait out this issue for a couple months. My dealer thinks I'm nuts to believe anything on the internet, but they won't be there to push when I'm broke-down in the middle of nowhere.

Well I'm kinda trying to swing a deal on a WR450 but I'm a little spooked by this too. It's not like we ride this things at the MX track where you can push back to the truck, put a new one in like a spark plug, and be back at it. But it does seem the majority are holding together.

The early numbered bikes apparently went to the east not many people out yet we've had ours since early feb, the 10th I think, and the first time we could be in a parking lot (when it failed was March 1). I've been thinking about this (in between prepping ol reliable, KTM400exc,) and I've got it narrowed down to two things with a test. If it's a heavy rotor I should be able to replace the key and remove the idle gear 2 which will take the electric starter and the starter clutch out of the circuit. The starter clutch is a one way clutch (spins one way not the other)if you get this backfire (I did not but it seems one fellow on TT had a backfire and damaged the starter gears as well as the key) that it might shear the key. Hey Guys this is all speculation until we can run some controlled tests. I for one will try removing the idle gear 2, bearing and shaft and see if I can shear a key. I was riding the bike at the time the key sheared and think I can do a good job duplicating it. If I don't shear a key then I'll put back in the the idle gear 2 and try to shear the key again. If one way I can shear a key more than once that's at least pointing us in the right direction. More as it unfolds

Excellent work and analysis, Wrench...Good luck with the wrench.

Just returned from dealer with my second new woodruff key and rotor is now lapped per Yam Tech instructions with loctite. I also spoke with Customer Relations and they said they will make this right no matter what it takes. I'd recommend everyone call them to complain in addition to working through their dealer. Yamaha cust relations is 1-800-962-7926. Heading to Daytona to give big blue a good thrashing.

i just got off the phone with customer relations. they aren't tech's ,they're people that don't know the difference between a woodruff key and a muffler bearing, they said they had heard something about a fly wheel problem and there advice was to bring it to my dealer and have the dealer call a yamaha tech.i spent $6000.00 plus they should come to my house and check out the bike . it's funny how yamaha hasn't faxed over anything admitting to a problem but they tell the dealers that there is something wrong with the flywheels.i could see if it was an iscolated case but it looks like everyother bike on here has sheared a key or that means half of us have very expensive paperweights right now. "hey yamaha you have a problem with your bikes fix it damn it". would this be a case for the whole lemon law thing? this is very aggrevating having this new bike we all have been waiting for, for months and delay after delay we still waited than it finally gets here and now we gotta wait for a fix !! it didn't bother me as much 2 weeks ago cause i had 2 feet of snow on the ground but now it's almost all gone and i could be riding now but i can't. the whole 14.3 miles i put on the bike were just a tease . this sucks and yamaha had better figure something out quick because if not there gonna have some really bad publicity after this. ok i think i feel a little better after ranting and raving.... no i don't i want to ride my bike !!!!!!!!!!!!!!!!!!!!!!!!!

:D:):D:cool: :cool: :cool::D :D :D:(:D :D :D :D :D :D :D :D :D;):p:D:cool: :cool: :cool: :cool: :cool: :cool: :cool: :cool:

"would this be a case for the whole lemon law thing?"


Class Action Lawsuit...

I would agree that all of the owners of WR450s should call Yamaha and put them on notice regardless if you have had a problem. I have not had any problems with mine, but like the rest of you guys, everytime I ride, I think about it. Maybe if enough of us call things might happen.

Up here in the Great White North we are hearing there may be two issues associated with the woodruff key shearing. Problem A - too lean pilot jet causing backfiring on start.

Problem B - battery not initially charged properly causing undervoltage conditions leading to backfiring.

Solution - lap flywheel and torque to correct value. Please be aware that just because you set your clicker torque wrench to 47 ft/lbs doesn't mean you are torquing to that value. I work in the nuclear industry and we check all our torque wrenches against a strain gauge for correct calibration and I almost never get a true reading from what is indicated on the dial. If you do not back off the clicker torque wrench every time you use it the dial setting is basically useless.

Battery voltage must be greater than 12.8 vdc. If not recharge with a GOOD quality battery charger.

Having said all this the Canadian bikes use a completely different ignition mapping program and use different jetting.

not to be difficult.. but if they recognize a jetting problem and a voltage issue, why does the solution include lapping the rotor? There is a third issue implied there as well as the first two.



it should be obvious to everyone by now that due to the weight of the flywheel a backfire will cause enough shear stress to fail the woodruff key if the taper fit is not ideal. most machinists will tell you that when machining a taper fit the final step is to lap the two surfaces to ensure a proper fit due to inperfections in the machining process due to worn cutters etc, etc, etc. only by lapping can the fit be precise enough to create the strong bond that holds the two pieces together. it would appear to me that the if the fit is corect the parts will not fail but it takes careful preparation to do this. i used to own bultacos in the past and this problem was very common. i used to have to carry woodruff keys in my bum bag until soomeone told me to lap the flywheel to the crank and I never had another failure.

from the rumours i am hearing there appears to be a tooling error within a certain range of engine numbers. in the end the jetting issue, possibly low voltage on the battery (the gel paack battery actually runs at a slightly higher voltage than your car battery) and a fit issue leadd to a number of failures.


Totally agree with the machining error statement. If I buy a bike over time it will backfire, get a low battery charge and many other issues. If it shears a key in conditions less that prefect this is not acceptable. Blaming this on lean jetting etc. is crazy. I know nothing about E start on the WR or similar setups. But if it is similar technology, has worked in the past on other models them the WR problem has to be in the Key, the mating surfaces or the weight of the flywheel. This torking and lock tite is not the answer. If the unit is made correctly 10 lbs of tork would be plenty. Now if the design is new (perhaps the E start won't release or go backwards when it backfires, this could be a problem). I took the flywheel off my WR400 and nearly needed a truck to get it off. You could use a toothpick for the woodruff key and never have a problem. I am sure this is a minor machining problem and the fix will be out soon. In the meantime I will carry a tow strap on the 426. At least the rescue vehicle will be Blue.

Just a thought, but if there is a backfire and the starter mechanism locks the flywheel and the piston still wants to turn the crank, it looks like the key may be failing because the crank is slipping but the flywheel is locked in place because of the starting mechanism. Maybe the key is breaking to protect the starting gears.

Bean, You have caught on! This is the cause from what Yamaha is saying. I happen to agree. This issue is getting blown out of proportion. We still need to ride Yamaha, but in Beans statement the cause is shown. ---Mike

Superbike and Bean,

Roger that explanation. Good deduction and reasoning. Iv'e replaced the key and used locktite the nut on my 03' WR450, but as you explain, the engineering flaw will cause the key fail anyway. Perhaps they should have engineered the starter to free-wheel in the reverse direction ? However, the inertia and speed at which that would happen is beyond the capability of that "juice-can" sized starter. How about a car-like selenoid to engage and withdraw the starter ? Are other bikes like that ? Iv'e placed 80 miles on the bike since the re-tourque but it is now on the stand until this is resolved. If not, I'm tempted to pull off the starter/battery and kick start the bike. Weight savings ?

HighPlainsWr, I may be on to something else. The First 3 times I checked my flywheel torque it changed. Now after riding a litte in my backyard, about a mile or two each time, I've been checking flywheel torque and it has remained the same. In other words it appears as if the flywheel has needed seating. Just my 2 cents.I have a race 3/16 at Budds Creek and not much time for break in.

After returning from dealer with a lapper flywheel, retorque to 47 lbs and loctite, sheared yet another woodruff key at around the 16 mile marker in Thursday's Alligator enduro (Daytona, FL). This time I did NOT use the e-start. The total now is 120 miles and three woodruff keys. Once again had to be towed out! Found a head Yamaha tech at Friday's road race and had a nice long heart to heart. They are now going to send a tech to my dealer to inspect the bike. They seemed surprised to learn I had the problem without using the e-start. Discussing problem with several road race mechanics over the weekend, a prevailing theory is the crank is now damaged and lapping will never work. Anyone else had a problem after lapping? :D:):D :D

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