WR450 Serial Numbers, Flywheel torque, key failure

when did you get your WR450, what are the last 4 digits of the serial number, did you check flywheel torque,

picked up in crate 2/10, 0413, less than 47 lbs, tightened to 47 loosened and retighten to 47lbs. no key failures

Setting the bike up now. Will check the torque before I start it. Some people are inspecting the woodruff key. Probubly a good idea.

I wasn't planning on taking the sidecover off, but I'm reconsidering. My updated insert says to just loosen and re-torque the rotor nut to 47 ft lbs. I'm not convinced this is a, torque only, problem.

Given the recent post pertaining to the less than precise fit between the tapers, I think some spotting dye and lapping compound will be in order to distinguish the quality of fit between the spindle and flywheel.

To those who have done that, any problems?

Serial Number 1041, got bike January 16, didn't check flywheel/key, I've got 78 miles on her with no problems.

I have #994 and the dealer re-torqued on setup. Just a theory but, the WR has a heavier fly-wheel than the YZ along with lean jetting. The lean jetting makes you have to add throttle to E-start then it backfires on starting etc. (mine wouldn't even E-start with stock jetting.) This may have put more stress on the key than expected causing the original torque from factory to be inadaquate. It would be interesting to find out if any non-US WR's have had key shearing or a retorque paste sheet. There is a post of someone having 2 keys shear, I wonder what jetting is in that bike. Also my manual and attach sheet say the correct torque is 61 ftlbs not 47.

Jonesy makes a good suggestion, any Canda or europe models had a key failure? Our bike (0413) hasn't been fired yet, first it got stripped to grease all bearings and torque all the bolts, then the carb was pulled and jetting changed to 48/160 and removed snorkle and baffle. Pull the mag cover off last night to check the rotor nut it came of before 40 ft lbs I removed it and tried to pull the rotor off but couldn't retorqued the nut to 47 loosened and retorqued to 47.

Believe it or not, but this all sounds very similar to the problem that plagues the Polini 50cc mini-race bike. It uses a centrifugal clutch and relies on a woodruff key. You can count on failure and frustration with them. :)

Cobras, on the other hand, use an almost identical centrifigul clutch, BUT their's relies on a tapered press-fit (no key at all). It is the most reliable in the class. We have experienced zero failures on our 3 Cobras in 4 years. It is especially strong when used in conjunction with a drop of red loctite.

Do not lightly dismiss the 50cc strength here: Their clutches generate FAR more heat than any of our bikes! So much so, that the ignition cover should be removed after races to prevent the heat from the clutch that transfers through the crank from cooking the PVL ignition while sitting.

The clutches on these racers (our Cobras at least) are set up to engage ONLY at high rpm, allowing the little motor to be well into its powerband, since it does not have any low-rpm "pull". This is a violent engagement much like revving our engine and just dumping the clutch. And it endures this every time the throttle is let-off then twisted! Every corner, etc.

The point is, the "fix" for this 450 problem may be to somehow eliminate the reliance on a woodruff key (very weak) and adopt a press-fit taper approach. It is much stronger.

Just my thoughts...

It is a press-fit taper approach, the woodruff key is only for timing alignment.The problem is poor fit on the taper evidently.

Mine is #0986 and this issue was addressed at the dealership 1/28 as a preventive measure. They called Yamaha at my insistance, and to their surprise Yamaha had me bring the bike in as soon as possible and they pulled the flywheel off and on several times and retorquing it to 47 ft-lbs. They didn't say anything about lapping, but I hope thats what they did... I have put on only about a 100 woods miles on the bike since then but no trouble yet.

This is a killer bike and I can't wait till I never read "woodruff key" again.

If that is true (and I don't know, just thinking out loud), why not use the 61 ft.-lb. torque in stead of the 47 ft.-lb. torque? If someone would tell me the material and thread size, I'll look up the max torque you can put on this thing. Just guessing, I bet it's close to 90 ft.-lb. safe torque limit.

if the surface of the flywheel taper doesnt perfectly match the taper of the crank....more torque means nothing.

The key is only used to position the flywheel. The conflicting torque numbers would make me believe that is where the problem lies. Modern quality control would catch an improper taper long before it reached production,(this isn't GMC you know).

Why would 14lbs less torque solve the problem???

If wrench couldn't torque it to 47 until he loosened it first, perhaps the problem is in the nut? Maybe the nut had burrs on the threads, making it appear at the factory to torque out at 47 before it actually was 47?

Just thinking out loud here.

if "modern quality control" was used......we wouldnt be having this problem in the first place

That is exactly how the failure-prone Polini clutches mount: a taper that does not provide enough of an interference fit with a key for alignment. The badly matched press-fit puts the stress on the key.

After it has broken loose and spun a couple of times, the situation becomes worse. You quickly lose what little press-fit there was to begin with. My friend's 2 sons raced Polini's for years and (ask any Polini Dad) the weak link is that poorly fit clutch, and once it starts being a problem, it never stops.

It is a source of endless frustration.

It seems too common to machine such pieces incorrectly with the assumption that the woodruff key (good for alignment only) should bear the force. That is nowhere near as strong as a properly matched press/taper fit accompanied by sufficient torque. I have seen woodruff keys that prevented the gear from going on far enough to accomplish a proper taper fit. They aren't supposed to. Nor are they the "shear-pin type of safety valve" others think they are. If so, why is the shaft tapered at all?

I understand the bulletin saying "torque it down to seat it, then back it off and retorque". But to decrease the overall torque makes no sense to me either.

Use some machinists bluing and torque the nut and gear into place. Then remove and see how much surface contact there actually is.

If there is a proper fit, like on the Cobra, you should need to use heat and a puller to even remove it. I don't have one of these bikes (yet), but Yamaha better step up and fix this pesky problem before they get a bad rep! It really is a piss-ant problem, but with the potential for great collateral damage.

If something is designed to be held together at a certain torque value, and that value is not held, (be it high or low), then it will not perform as it was designed. If two tapers are designed to be positioned at 47 lbs. and you crank in 61 lbs. that flywheel is not in the correct position. Put a sensitive indicater on that flywheel while you torque it and watch it slide into position. It needs the correct torque, no more or less.


you seem like an intelligent person. Why do you ride a XR650??? :)

Guys, let's be honest, the guys at the factory are using air wrenches set at an air pressure to get close to there specified torque. They may have had a problem in the line. BTW burrs would have caused the torque to seize faster giving a false torque. They could have even stoped the nut before it bottomed. Who knows? Lets assume it was not a production line problem, because if it was, there are all types of variables that could have happened. Truth is, we have a design problem, and only Yamaha know what that is right now. Is the Key a restrainer or a alignment Key? Or is the taper not engineered correctly? I have not ridden my bike enough to have a problem. I did jet to 160/48 and it does have a bog off idle. I have ordered three Jet Needle's to try. Although the backfire problem may be causing the Key sheer, It is still a bad design. I don't think it is a problem we can't overcome, but it would help if Yahama would give us a little information on!!!!! I'll bet they know and are trying to keep the Hoopla to a minimum. I think the thread on Serial Number is a good thing, because it will tell when they fixed the problem.

Dutch, I disagree. More torque would help if the holding power (friction fit) is ment to hold it. I'm not sure right now that is the case. Although the Key is normally a tool used to Keep anything more damaging from occuring. You see right now we don't know the design. Is it a friction fit problem (tapper) or is the Key supposed to take the blunt of the force? I would have to assume the tapper is the problem and the Key is just that a Key to clock the possition.

So do you guys think its a good idea to put a dab of lock tite before re torqueing? :)

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