Author Topic: Tapered Steering Head Bearing Adjustment ( ST1100 ) *  (Read 4893 times)

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Tapered Steering Head Bearing Adjustment ( ST1100 ) *
« on: April 04, 2009, 11:56:27 AM »
Original article can be viewed here:
http://home.insightbb.com/~mmartin36/Taper.htm

Submitted by Mike Martin.

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Tapered Steering Head Bearing Adjustment

The Honda ST1100 service manual specifies 20 lb. ft./28 Nm torque for the original equipment steering head ball bearings. This torque is much too high if you use tapered roller bearings when you replace the originals, though. In either case, after installation the procedures in the Honda Common Service manual (page 18-22) call for checking the steering bearing preload with a spring scale pulling forward at the top of one of the fork tubes. The ST1100 service manual specifies that the preload should measure 1.5 to 2.0 kg. (3.3 to 4.4 lb.). Not having a spring scale for this test, here's what I did after installing tapered steering head bearings. The following adjustment procedure will be appropriate for the ball bearings as well.

1. Tapered roller bearings need very little, if any, pre-load. The taper creates a powerful wedge effect, and the bearing load goes up quite rapidly with pre-load. I initially applied 20 lb. ft. to seat the bearing races, but reduced the torque to finger tight before installing the locking washer and lock nut. Then I adjusted the bearing pre-load so that the handlebars would just fall to the side when pushed off-center. This was with the bike on the centerstand and the front wheel jacked up off the ground. Note that you do not want any clearance in the bearings, because that will cause them to hammer when you go over bumps. You need some pre-load, but not as much with the tapered roller bearings.

2. Anyone who has ever played with adjusting bicycle wheel bearings (trying to eliminate free play while minimizing bearing drag) will understand what I will attempt to describe next. There is a bit of clearance between the threads of the steering bearing adjustment nut and the threads on the steering stem. When the nut is installed, the weight of the front wheel and forks (plus any installation bearing pre-load) causes the thread contact to be between the lower side of the stem threads and the upper side of the nut threads. Then, when the lock nut (or the nut atop the fork top bridge) is installed at a much higher torque, it forces the adjustment nut downward the distance of this thread clearance, increasing the pre-load in the bearings. After snugging the lock nut down against the locking tab washer, I had to tighten the lock nut a lot in order to get the locking tabs on the washer to line up with the slots in the lock nut. I tried inverting the locking nut to see if that made a difference, but there didn't seem to be any. As the nuts are forced together, they can dilate a bit with further tightening torque to allow the tab to align with a slot. What is important is that the nuts are forced together. That prevents the pre-load from changing after installation of the top bridge, creating too much bearing pre-load.

3. Excessive pre-load will do two things. The lesser problem is that it may shorten the bearing life. But, more importantly, it will create enough friction in the steering that the motorcycle will not track properly. This will be more noticeable at low speeds, when the self-centering from the steering geometry has less effect, and you won't be able to ride a very straight line.

4. The work-around for this was to use a large pair of Channel-lock® pliers to turn the adjusting nut to achieve the pre-load as described in (1). Note that the final adjustment was made after the lock nut was tightened and the lock washer tabs engaged. Both nuts are being turned simultaneously. After the pre-load was set and checked, installation of the fork top bridge (76 lb. ft./105 Nm) did not affect this pre-load adjustment.

Incidentally, my Haynes manual says to check the bearing adjustment and re-adjust if necessary after installing the fork top bridge. So it's not a case of using a given tightening torque value and knowing that the pre-load is properly set.

© 2002 M. E. Martin, All rights reserved
« Last Edit: January 28, 2013, 08:01:37 AM by Tom Melnik »