I know things... A lot of things.
Join Date: Feb 2015
Motorcycle: GSXR 750 K4
Some notes on steering bearings
So I finally came round to getting a proper tool to adjust the steering head bearings with my 1/2" torque wrench. The main reason, besides convenience, was that I noticed that the manual prescribed a torque of 80Nm for the steering stem locknut on my K4 750. I figured that it was unlikely I would be getting even close to this value with a hook spanner, so perhaps that was explaining why I always had the feeling that the improvement I felt after tightening my steering bearings, seemed to vanish after a few days.
A drift or screwdriver and hammer would also work, but besides lacking in finesse, they don't allow any sort of method in the adjustment. That's because it's hard to tell how much you've tightened each component and since both the stem nut and the stem locknut contribute to the total preload on the bearings (and properly the stem head nut too), you're essentially left with trying at random, until you get a setting that's not too loose and not too tight.
A few thoughts on the procedure: It is my understanding, that the assembly is essentially that of three nuts in succession, with two washers in between. One is the washer between the stem nut and locknut and the other is the upper yoke, which seems to act as a washer between the stem head nut and the stem locknut (I'm using terminology from the service manual to avoid ambiguity here). What the point of this setup is, I don't know, but the manual specifically states that the stem head nut, should be fastened before the pinch bolts of the upper yoke, which should result in the yoke being tightened onto the locknut. The overall effect of this is that, as each nut is tightened each one contributes to the preload of the bearings.
This then means that the upper yoke should be removed, or, at least, both the stem head nut and the pinch bolts should be loosened before any attempt at adjusting the bearing is made. This is stated by the manual and it makes sense. What doesn't, is that the pinch bolts of the clip-ons should also be loosened according to the manual. One possible explanation, is that the clip-ons have locating tabs which might be resting against the top yoke, preventing it from being tightened properly against the stem locknut.
For me, the desired torque setting of the stem nut ended up being about 10Nm. This is very approximate, as it's the lowest setting on my torque wrench (which is of dubious precision anyway). Nevertheless about 10Nm seemed to be close to the threshold, where the bike started weaving at low speeds, wanting to fall into slow turns and requiring more steering effort. A smaller and better torque wrench might be useful here.
I have also puzzled over the purpose of the washer between stem nut and locknut. This has a tab, locating into a keyway machined into the stem, but no other tabs used to lock into the two nuts, as is usual. My understanding is that the locking effect is achieved through the increased tightening torque of the locknut and the purpose of the washer is to isolate the two nuts so that loosening the locknut in order to perform an adjustment, doesn't change the setting of the stem nut (as the washer is locked onto the stem and can't turn to transfer torque to the stem nut). Despite that, each time I've loosened the lock nut, the stem nut and dust seal turned a bit, or at least it looked that way. I can't explain how that could happen.
Not sure of the practical value of all this, as it doesn't really say anything more than the manual about the procedure. I've posted it here for whomever might be interested. Any thoughts and corrections are, of course, welcome.