Second Thoughts

hopefully, the west coast guys will get all this sorted out by the time i can actually ride my bike, when the snow melts. :)

I have the Yamaha yz450f/wr450f Technical Orientation Guide CD that the dearlers get. It has the assembly and shop manuals for the YZ450f (1st edition dated June 2002) and the WR450f (1st edition dated Oct 2002) and the WR lists the rotor nut at 50 ftlbs. SMD what edition is your manual? (in the first couple pages)

I have the 1st edition. One of the guys I ride with just picked his up this evening and his manual calls for 61 but is without the cut&paste / its original print. Go figure......

It's sounding more and more like we should be double-checking the tightness of that nut, just in case. Can't hurt, right?

let me get this straight.....are we talking about the nut on the end of the crank that holds the flywheel on ?

if so , whats the proper way to hold the flywheel to check the tightness of the nut ?

FLYWHEELS ARE SECURED TO THE END OF THE CRANKSHAFT BY A TAPER AND A NUT. THE TAPER BY ITSELF HAS SOME RESISTENCE TO KEEP THE FLYWHEEL FROM ROTATING ON THE END OF THE CRANKSHAFT. THE KEYWAY AND KEY FUNCTION IS TO INDEX THE FLYWHEEL TO THE CRANKSHAFT. INDEED IT ALSO AIDS IN KEEPING THE FLYWHEEL FROM ROTATING ON THE END OF THE CRANKSHAFT. THE MOST LIKLY CASE OF THE PROBLEM IS THE NUT HOLDING THE FLYWHEEL ON HAS LOST IT'S TORQUE OR WAS NEVER TORQUED ENOUGH AT THE FACTORY. I WOULD RECOMMEND EVERYONE TO CHECK THE TORQUE ON THE NUT AND ALSO USE LOCKTITE TO HELP ELIMINATE THE NUT FROM BACKING OFF.

THE MOST LIKLY CASE OF THE PROBLEM IS THE NUT HOLDING THE FLYWHEEL ON HAS LOST IT'S TORQUE OR WAS NEVER TORQUED ENOUGH AT THE FACTORY.

The bike backfires during starting, shearing the woodruff key, and just at that moment the mag nut comes loose, for a totally unrelated reason.

That would be one hell of a coincidence.

Does anyone know the material and size of the Nut/shaft? I would like to look up the max torque for this unit. If they have gone from a 50 FT-LB to a 65 FT-LB torque, they could be approaching the elastic limit of the material strength. Another possibility, the 50 FT-Lb could be the greased torque and the 65 FT-BL could be the dry/clean torque. I would suggest using the 50 ft-lb if you use any lubricant while torqueing this nut just to be on the safe side(loctight (sp) is a lubricant as you use it until it dries).

I was just looking through the PDF version of the WR250F manual and noticed the rotor nut calls for 61ft.lbs. of torque also. I'm going to loc-tite and re-torque just to be on the safe side.

EXACTLY......

Could not have been said better...

Bonzai :)

Old Huskys used to have this problem and alot of shops

used to use lapping compound to lap the flywheel to the crank shaft

my manual has the cut and paste.....61 lbs.

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