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Old 07-27-2005, 05:42 PM   #78
Caribou Aqua Buddha
Beastly Adventurer
Joined: Jan 2003
Oddometer: 22,983
I do not own a GS, but I feel your pain. I checked in my bearing books to confirm my hunch. The 61917 is a std (light) duty single row Conrad style ball bearing. In a perfect world the side loads would be accomodated by the tapered roller bearing on the other side. But the world is not perfect, and without perfect spacing, a side load can still devolope on that ball bearing. Ball bearings are not meant to take much if any axial load. I believe this problem is exagerated by the single sided swing arm.
On to the fix, as I learned in my bearing class at college last winter, repeated failure without contamination, installation damage, or electrical current passing through the bearing, to name a few, spells engineering problem, meaning bearing needs to be bigger, Max Capacity as it is called in the bearing world. The problem is, there is no Max Capacity replacement for this 85X120X18 mm bearing, I confirmed this with my instructor today. So in short the bearing dimensions change (larger) with a max capacity or other bearing type, so for a permanent fix the associated housing bores also need changed. I talked to some bearing guru's today and they arrived at the same conclusion,... more than a few random failures, assuming proper initial assembly,cleanliness etc, is an engineeing problem. The randomness of these failures actually supports that theory in my mind.
Anyway there is no better replacement than the stock FAG brand, especially considering that bearing was $200 at our local store. My instructor said the factory FAG or SKF would be about the same quality. And don't buy made in china bearing.
Also looking at my load rating specs in my engineering book, they could have went from 6,740 lbf to 22,020 lbf by choosing a max capacity bearing, the outer bore would have to be 30mm larger. In hindsight maybe a good trade off. Although I am not convinced a Conrad style ball bearing is even appropriate to begin with. Japanese bikes use a similiar inner ball bearing, but usually with a traditional double sided swing arm.
BMW needs a complete kit with the associated parts and different bearings, and maybe they are working on it. I doubt it will be free if they do.
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