Yamaha woodruff key Service Bulletin, finally!

Freshly scribbled down at my favourite Austrian yamaha workshop:

"mandatory Modification WR450F"

serial numbers affected: CJ04W-0000037 to CJ04W-0003669

model types: 5TJ2 and 5TJ4

needed parts:

90280-03001-00 woodruff key

5TJ-15451-00-00 gasket

needed tools:

90890-04141-00 flywhell puller

reason: the woodruff key may break (no reason given

only a pic of a single key with an odd stripe,

probably wear, on the brink of dying?)


- disassemble and remove stock key

- reassemble with new key according to the following:

- put Loctite 648 on key and whole crank taper

- place rotor onto crank

- torque rotor nut to 40 Nm (29ftlbs)

- wait 2 minutes

- remove nut

- put Loctite (no specific number given) onto nut and washer

- torque to 65 Nm (47 ftlbs?)

- reinstall engine side case (my assumption: here you

should use the gasket, advisory doesn't say so explicitly)

- and refrain from starting engine for 24h! (very odd)

end of procedure

No lapping, no reason what is wrong with initial setup,

no periodic retorqing requirements are given.

The document definitely is a locally generated one,

it doesn't bear the corporate look one would expect a worldwide item to have.

But it is denoted as a mandatory modification, the dealer is requiered to call customers of shipped bikes and there's a form attached which the dealer is supposed to send in for every repair he has done.

Personally i don't like that very much. It sounds like simply reasembling everything using a lot of glue. The required woodruff key has a -00 ending in its part number. When Yamaha comes up with some improved item they normally increment the trailing 00s. I'm currently not sure if it is a good idea to tear all that loctited things apart agains after my dealer had done the mod. But i would be much more at ease knowing the tapers are lapped and the key is okay. no risk no fun.


Here's what I don't understand. Is the problem due to an improper mating of the tapered surfaces or is it due to engine backfires?

The whole purpose for haveing a key is to allow it to sheer when too much stress is induced so as to save the crank and/or other other engine parts. So, if we "glue" the flywheel on and a backfire occurs, do we risk damaging the engine??

My initial reaction is that the obvious solution is a lighter flywheel in order to reduce inertia. However, we like the heavy flywheel. So, should we be looking for a compromise with the flywheel weight or not?


Rowdy, thanks for the post!!!!!!!!!!

Thanks for the post. I will wait to see if Yamaha North America does the same with our serial number units. I doubt they will recall all of them for service here in the USA.

Jimbo, When used with a tapered fit, the woodruff key is not supposed to absorb any load. It is not a safety shear. The taper is supposed to do the holding and is much stronger when you are talking these small sizes. If you break your taper bond, the key is a goner period. The key is for indexing only. This is opposed to how a harmonic balancer on a chevy small block mounts (for instance). There, you have a straight shaft and the key does the holding. A very large and strong key compared to the 450's.

If I owned a 450, I would absolutely want the shortest height woodruff key possible. I would grind it down so it just barely locates in the gear keyway. I would unhesitatingly use red loctite to mount the gear and the nut making sure the mating surfaces are brake-cleaner clean! Then leave 'er sit for 24hrs just for peace of mind though shouldn't be necessary, add oil and ride. If that arrangement failed, the shaft and/or gear hub are toast and anything short of welding is futile.

A proper taper fit is very strong and should absolutely require a puller to remove even with just 20lb/ft of torque on the nut. You have to heat the aluminum hub of the Cobra clutches with a small torch AND use a puller to remove them and they only use @20lb/ft but NO woodruff key on a very tiny shaft.

If the key on a taper shaft is even slightly too high, it will cause the gear to "ramp up" and disallow a proper interference fit. Bad deal. It totally defeats the purpose of the taper. It stands to reason that the gear would also be slightly cocked and not run true either, causing further trouble while increasing the likelihood of failure.

If you could very accurately measure the distance the gear goes on with and then without the key at equal torque with a dial indicator it should show some difference if the key is interfering. It would take very little difference (we are talking .001"s here) to compromise a proper taper fit.

Chaindrive, i totally agree with your opinion about a TAPERED fit using the woodruff key only as an alignment aid while putting the items together. A plastic key would do the very same job, alignment during assembly.

What bothers me more is that Loctite 648 is a very strong mounting glue "hard to disassemble with normal tools" requiring "300°C" for disassembly. While removing a nut secured with L648 seems to be hard but doable a tapered fit will certainly require quite some heat (bad for the magnets in the flywhell i seem to recall) making removal of the flywheel ordeal best avoided.

Admittedly, i didn't change the cam chain on my WR400F in +25000 miles but my XT600 thumper has a much heavier flywheel sitting on a tapered fit without noticeable amounts of Locite and i'd guess that a 600 cc engine will put much more stress on such a fit than a 400 cc. So why is a glueles, normal taper fit assembly apparently not providing enough of a saftey margin in our WR450F?

To me that reads as if even a perfectly lapped taper, complete with a nice and low profile key won't be able to do the job right, hence the request for L648.

I think the engineers ought have gone with a flatter taper when bumping up the displacement.

But as long as the yamaha workshop degreases the taper surfaces good before locititening and uses a correct key in their pre shipment routine i'll simply try not to worry.


Chaindrive big Thankyou for the informative post.......Hmmmmm.

great, so the recommendation is to put some glue on it. DO they also include free Bandaids?

Alabama, I noticed that you are using a 158 main jet where most others including me are using 160. You have also changed your needle position. I have noticed that I seem to be using a ton of gas compared to my WR426. Is this all due to a smaller tank and more displacement, or are we using too big of a main jet in your opinion.

Yeah, I see your point about the magnets, Rowdy. But I think I would take my chances on down the road regarding the magnets and heat. If it came time to replace the chain, you would at least have had the pleasure of wearing it out! When you consider how long it gets hot and stays hot while running, I think the magnets are probably pretty durable.

I think most 450 owners would love it if it took heat and a puller to remove that flywheel. It is not necessary very often and it really doesn't require prolonged high temp. The degree of taper engineered into the shaft would definitely have a lot to do with strength. But there is nothing we can do about that, except use every available means (short of welding!)to help strengthen it as much as possible.

I would like to see one close-up and in person. If the woodruff key is interfering, it MUST cause the flywheel to be minutely cockeyed, thereby enhancing the problem. That's a lot of mass at high rpm! Just like being out of balance. Like a car with a bent wheel or axle shaft. No way that will last long. I wonder if the runout has been measured with and w/o the key installed?

I have done the Cobra clutches w/o loctite and not had any problems, but it does give a little extra margin and peace of mind. Those clutches must be removed very frequently to clean and replace the spring-washers regulating clutch engagement.

The heat generated by the centrifigul-clutch on these single-speed minis is so intense (way beyond anything endured by a normal clutch) that it is highly recommended practice to remove the ignition cover on the other side of the motor in between motos to prevent the heat transfered through the crank from cooking the ignition stator! It really can! And PVL claims their ignitions are made with the highest heat-resistant space-age stuff available, but still strongly advise getting that cover off.

I know it seems kind of absurd to keep comparing this problem to those little minis, but they take a helluva beating on that clutch assembly when set for a proper racing, high rpm engagement. I set ours up to launch violently (causing repeated impact/shear engagement on the tapered fit) and the bike must be kept on the pipe for full lockup. The little buggers really scream! A far cry from a Suzuki, Yamaha, or Honda 50, which aren't competetive race bikes. Not even close. But good learner bikes.

I know it seems kind of absurd to keep comparing this problem to those little minis,

Not at all Chain, you keep comparing cause it's giving a lot of us that have nothing to compare to insight. Thanks for your info.

I pick my bike up tomorrow with my "glued on"flywheel. this bike is so much fun, I hope it holds. I had around 400 miles on mine and I thought it would never break...Yamaha is taking care of the labor and parts(past the 30 day warr.). I am paying for the red label shipping so I can pick it up Weds. I can't wait. Must ride,must ride.

Well Florida you just helped me make up my mind which bike to take to Utah and it wont be the new WR450. For shame, for shame, for shame. I have about 350 miles on my new unit and about 120 of them are race miles. But if yours sheared at 400 I am not going to take the chance of making my friends have to help me deal with getting my new $7000 bike back from the middle of BUMFORK UTAH. This may work out allright but Yamaha is losing much face very rapido. I have never bought a first run bike before and right now I hope from now on all new Yamahas sit on the showroom floor and rot. Goober

Does anyone actually have the content and number of the flywheel / woodruff key failure TSB. M2003-005 is just the insert to the manual changing the torque value from 60 to 47 f/lbs. If anyone actually has it please post.

I designed rare earth magnetic separators for the mining industry for almost 10 years. As the strength of a magnet increases, the ability to resist demagnetization due to heat, decreases. Very strong, permanent rare earth magnets with a strength of 40 Megagauss will demagnetize at about 200 degrees C.

Just to give you an idea of the strength, these are the type that are strong enough to squish skin off of a finger if you get caught between them in small sizes. In larger sizes, 2 coming together will crush and remove fingers.

I'm guessing the magnets in the flywheel are ferrite (weak) and should resist demagnetization at that temperature. There are charts that list the properties of these magnets so you can determine their strength and demagnetization temps.

What I don't get though is what about the bikes outside of the stated range?

I havent yet checked the serial number on my new beast but I am guessing as its an Aussi model it is a later number.

Did they have a bad batch of flywheels or crankshafts?

If not, then why wouldnt they apply the TSB to all WR450's .... :D:)

I'm no mechanic but my riding buddy is and he looked at the starter design and feels this is the real issue since the starter stays engaged while running. He said the problem is there is no bendix on the starter to dis-engage.

All I know is my bike is in the shop and it is going to be 77 degrees this weekend here in No. Cal

He said the problem is there is no bendix on the starter to dis-engage.

Bendix? You mean like the Yamaha Virago? I'll take the WR450 setup over that any day! Virago: CLACKETY CRUNCH CRUNCH WHACK ZZZZZZZZ CLACKETY CRUNCH CLACK ZZZZZZZZZZZ :)

I've had mine kick back numerous times since the repair and it didn't shear the key. No full backfires yet, but harder kick-backs than what sheared the key the first time. I think it's fixed.

In my opinion, I think the one-way starter clutch should have some slippage under excessive torque. That would have saved the woodruff key and in those rare circumstances when it slipped too much to start the engine, I'll just use the kick starter.

I live in Virginia, but bought my WR450 (#418) at Brewer Cycles in Henderson, NC. I called their service dept today to ask them if they'd gotten the service bulletin on the woodruff key. The guy in service told me he hadn't seen it yet, but that they had heard of a possible problem. He told me they had swapped mine out the day before I picked up the bike! Talk about service!!! This is the same dealer that called me and offered to do the throttle stop, exhaust baffle, and gray wire mods before I picked up the bike! It's about a 2.5 hour trip for me, but I'm glad I spent my money with folks like that! Pretty cool.

RE: Hangtown

The Correction sheet regarding torque change to 47 ft lbs from 61 is not a service bulletin, and has no number that i'm aware of. The release date of this document was prior to 1-31-03 (I picked my bike up on that date and the correction sheet was in the manual package.) TSB number m2003-005 was released on 3-7-03 according to the cust. svc. rep I spoke to this morning at yamaha. It is available to your dealer either on the dealer website, or by contacting their regional service rep. Now as far as the actual contents of the TSB, its still just rumour and conjecture.



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