1972 BMW R75/5 - Steering bearing replacement
Realizing Die Hexe was exhibiting the following issue with notchy steering...
Brinelling is a material surface failure caused by Hertz contact stress that exceeds the material limit. This failure is caused by just one application of a load great enough to exceed the material limit. The result is a permanent dent or "brinell" mark. It is a common cause of roller bearing failures...
http://en.wikipedia.org/wiki/Brinelling
... led me to investigate how to replace my steering bearings. Initial readings indicated this problem was huge and required a tremendous amount of brute force hammering, cut off tools, torches, freezing and re-heating components, etc. etc.. Instead, I purchase the following jig / tool.
STEERING HEAD BEARING PULLER SET - 1970-1995 AIRHEADS - $85.00
Includes both the outer race and inner race steering head bearing pullers, plus everything you need to reinstall the races in the frame and the bearing on the triple tree. Makes this onerous task quite a bit less so...
http://www.cycleworks.net/
This jig made the potentially difficult task of removing and reinstalling my steering bearing racers far, far less so.
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Fast forward a couple of hours, everything is back together and resting after a quick 50 mile test run. She's handling better than ever before.
Preload bearing settings are still a bit of a mystery to me. The exact bearing preload is unclear and, perhaps even more so, uncertain how to set given the steering nut. My thoughts are simply to over tighten the preload and back this off a smidge. Ride this for a bit and monitor any slop. The following snippet from Duane's site seemed useful enough as a guideline to follow:
Adjust it to the correct amount. The longest life of a taper bearing is with a tiny bit of preload. That means to tighten it to some small amount beyond the point of no free play. How much is the question. If you have just replaced the bearings, I suggest that you over tighten the bearings and then back off to what you need. This will help assure that they have seated properly.
In either case, the correct tightness is so that no free play exists. Free play is hard to detect accurately while the bike is sitting on the centerstand, but one can get close. Just grab the lower fork legs (castings) from the front and pull towards yourself. If you still have the adjustment loose, then you can feel the play. Have your friend slowly tighten up the adjuster while you are checking the play. You may be able to get it really close, but don't be discouraged if this doesn't work for you. My highly experienced mechanics sometimes had trouble getting it exactly right the first time by this method.
Once the bike is together, you may roll it forwards and gently apply the front brake. If you feel a tiny click or movement, that is the play. Free play will be noticed by a shimmy, or shudder, in the front end while applying the front brake. It is possible that a shudder is really a brake drum that is out of round, see below. Extreme over-tightness will be noticed by the forks not swinging totally freely while the wheel is in the air, such as on the center stand. It will be similar to some tightening of the steering damper. There is some amount of tightness between perfect and the extreme. I can't tell you how to detect that situation. It can be avoided by tightening only to "no free play" and then tightening the large nut properly.
Note. You can find another way of setting the preload on the steering bearings by one of the well respected experts of BMW. Basically it is to adjust it tighter until the forks stop flopping from side to side and just gently fall to one side. We found a variable in that procedure due to the weight of the lube, temperature of the lube, routing of cables, hydraulic lines and wires that would affect the resistance to falling to one side. This "falling slowly to one side" is not reliable.
http://w6rec.com/duane/bmw/steeradj/