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Steering bearing install/setup

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Greetings:

I'm looking for specific information regarding the install of the CRF250X headset: Preload torque and top nut torque. I don't own an -X myself. The questions came up on someone else's bike.

I've searched TT..found things like 'I just give it a good tug..' and 'I tightened mine to 100ft/lbs this time..'. I've been told the manual specifies a torque of 80ft/lbs for the top nut.

Most of that seems incredibily excessive to me.

What's at issue: After the preload is set by the spanner nut, after the top triple is placed on the stem, a torque of 80ft/lbs on the top nut changes the preload! That much force increases the bearing drag a LOT.

Seems strange that, having gone to the trouble of adjusting the preload in the first place, you completely negate that setting by reefing on the top nut.

And...where does the difference in play come from? The spanner/stem threads are that sloppy?

I have never seen a bike that, with steering stem bearings correctly installed, showed significant resistance in lock-to-lock movement with the forks and wheel attached. Usually, you can barely feel resistance in the tree without the forks/wheel attached.

(That said only as a reference to 'feeling' of resistance. You don't tighten the top clamp before you put the fork tubes in and center/align the front assembly.)

My Kawasaki has a steel stem, a 30mm top nut tightened to a 33ft/lb. spec. That process results in NO change to the preload/tapered roller tension.

How the CRF stem (aluminum) can take 80-100ft/lbs on that 32mm nut I don't get, either. Seems you would need a nut 1" tall to be able to squeeze it that hard and not damage something.

Please: Can someone confirm the 80ft/lb. top nut value, and tell me how their preload lock-to-lock turning force changed with that top nut value applied?

Much appreciated.

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Here's the relevant page from the CRF250X 2004-2008 Service Manual:

CRF250XSteeringStemInstall.jpg

I've used this exact procedure with the numbers shown and have had no problems. However, I do note that the step that reads: "Insert the fork leg (page 13-29)." will have you tightening the upper pinch bolts before setting the stem nut torque. I always do it in the other order: tighten stem nut then tighten upper pinch bolts. I want the upper bridge to be free floating on the forks when I set the stem nut torque; I don't want it to be loaded by the stem nut.

I think the 5.1 lbf-ft on the adjusting nut is the key step.

Note: the book shows 'Insert the fork leg' and really should show 'Install the fork legs', but I think the meaning is clear.

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Yes, it does say 'install fork leg'...but it does NOT say 'tighten the pinch bolts.' :ride:

Your procedure:

I always do it in the other order:
is correct for the exact reasons you list imo. At least, I agree with you about 'em...NOT the manual if indeed their 'install fork leg' includes tightening the top pinch bolts. 'Install' certainly sounds like tightening the clamp pinch bolts would be part of it, but it doesn't specifically say to do so.

Then...it doesn't appear it says to do it later, either.

The 80ft/lb part still amazes me. I don't understand why that much force is required.

Have you noticed a difference in the bearing adjustment (force to move/feel) before and after tightening the top nut to that 80ft/lbs?

I'm saying there should be no (precious little) difference before/after, else tightening the top nut has interfered with the preload 'adjustment'...and that indicates an error somewhere along the line.

FWIW the bike in question did have the bearings replaced. It was not only a lubrication issue. Don't see what difference that would make....

Thank you for the manual excerpt!:cheers:

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At least, I agree with you about 'em...NOT the manual if indeed their 'install fork leg' includes tightening the top pinch bolts. 'Install' certainly sounds like tightening the clamp pinch bolts would be part of it, but it doesn't specifically say to do so.
Actually, the fork installation does include tightening the upper pinch bolts.
Have you noticed a difference in the bearing adjustment (force to move/feel) before and after tightening the top nut to that 80ft/lbs?

Yes, it does tighten up. But then, I thought it was too loose at 5.1 on the adjusting nut. So for me, it ends up right where I want it.
I'm saying there should be no (precious little) difference before/after, else tightening the top nut has interfered with the preload 'adjustment'...and that indicates an error somewhere along the line.
Assuming that they really want those upper pinch bolts tightened first, then they may be taking into account the flex in the aluminum top clamp and how much torque it takes to get the preload right. Perhaps loading the top clamp provides some stiffness in the whole assembly...

Honda does have extensive experience with aluminum (frames, for instance), so maybe they're much more on top of it than we would ever imagine. :cheers:

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I always wondered about the 80 ft-lbs....it seemed like overkill but you might have explained it.

I've seen a couple of used bikes now that have bad steering bearings where people only torque the nut sparingly so the steering feels smooth....enough to get by selling it without the buyer knowing. Then once the guy buys it and tries to torque it down to 80 ft-lb...the bad bearing feel really becomes apparent. Anyway...its one more thing to check when buying a new bike....if that nut is loose at the top, it could be a sign that bearing replacement is in your future.

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