WR450 Serial Numbers, Flywheel torque, key failure
Posted February 11, 2003 - 05:28 PM
picked up in crate 2/10, 0413, less than 47 lbs, tightened to 47 loosened and retighten to 47lbs. no key failures
Posted February 11, 2003 - 06:43 PM
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.
Posted February 12, 2003 - 04:59 AM
To those who have done that, any problems?
Posted February 12, 2003 - 05:44 AM
Posted February 12, 2003 - 06:06 AM
Posted February 12, 2003 - 06:33 AM
Posted February 12, 2003 - 10:39 AM
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...
Posted February 12, 2003 - 02:35 PM
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.
Posted February 12, 2003 - 02:51 PM
Posted February 12, 2003 - 02:56 PM
Posted February 12, 2003 - 03:15 PM
Posted February 12, 2003 - 03:39 PM
Just thinking out loud here.
Posted February 12, 2003 - 03:54 PM
Posted February 12, 2003 - 04:01 PM
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.
Posted February 12, 2003 - 04:04 PM
Posted February 12, 2003 - 04:17 PM
you seem like an intelligent person. Why do you ride a XR650???
Posted February 12, 2003 - 04:18 PM
Posted February 12, 2003 - 04:28 PM
Posted February 12, 2003 - 04:45 PM