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Thumper mike

Steering stem nut won't stay tight

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Bought a 2006 yz450 1 month ago. Previous owner had installed Applied Racing triple

clamp upper and lower. The problem is the crown nut on steering stem will not stay tight. It will loosen up after about 10 laps. What could be causing this? I plan on taking it apart next weekend, just wondering what to look for. Thanks

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If everything is properly installed and torqued correctly it should not be a problem.  With that being said I had an aftermarket triple on my 07 and it seemed to always come loose.  I drilled and safety wired it an never had an issue again.

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First, loosen the top clamp at the fork tubes, then loosen the crown nut.  Set the bearing pre-load ring to roughly 5 ft/lb of torque as well as you can.  Then tighten the crown nut to 105 ft/lb, THEN tighten the pinch bolts at the fork tubes to 17 ft/lb.

 

Check the tension on the head bearings at this point.  The steering should be just tight enough so you that with the bike on a stand, can put the front wheel in any steering position and not have it flop over against the stop.

 

There are two possible reasons for the crown nut to loosen.  The first is incorrect assembly.  If the top clamp pinch bolts are not loosened before the crown nut is tightened, the tension on them can keep the top clamp from being clamped to the bearing adjuster squarely, and it can scrub and work loose.  Also, the crown nut needs to be tight.

 

The second reason would be if one or more of the bearing races was not completely seated in the steering head or on the stem. That, however, should also cause loose, clunky head bearings.

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