senseamidmadness
Neglected Bike Adopter
I have another question for you folks, related to bulletproofing the transmission in my 1997 R850R against future wear when I open it up for service, but this would apply to any M97 transmission owner who has to open theirs up so I figured I'd put it in its own thread.
This is about the known issue with M97 Oilhead transmissions where the input shaft gear eats its way into the adjacent bearing on the rear of the input shaft, documented by Anton Largiader here: http://largiader.com/tech/oiltrans/m97.html
Anton, on his website, details the updated gear part with a larger surface area and no internal chamfer as fixing the problem. Unfortunately, this part is very expensive (currently priced by BMW, the only reliable source, at $330, plus shipping, plus tax, plus waiting-a-month-for-shipping).
I found this thread on the BMW Sport Touring forums from way back in the mid-2000's regarding this same issue, and an unorthodox (and much cheaper) attempt at solving it. https://www.bmwsporttouring.com/topic/13441-chocolate-gear-oil/
In this thread, user smiller details his attempted future-proofing: replacing the wave washer on the input shaft with a solid 3mm shim, at the expense of slightly more gearbox noise while in neutral. He theorizes that the spring tension of the wave washer allows a "hammering" effect where the gear repeatedly slams into the bearing when load is suddenly placed on the transmission, and that replacing it with a solid shim prevents this entirely. His reasoning is that the M94 input shaft had a very similar design but no wave washer and did not have this issue, and that the wave washer was only installed to quiet down the gearbox clatter while idling in neutral.
He also said he had done this fix to a couple of transmissions, including his own, that had failed input shaft bearings as part of rebuilds, and was planning to re-open his over 20,000 miles later in order to gauge whether it successfully prevented the wear problem. The only detriment to the fix was a significant increase in transmission noise in neutral but he considered this to be worth it.
Edit: Another transmission rebuild thread on ADVRider also mentions this solution with a nice picture: https://advrider.com/f/threads/i-took-apart-an-m97-transmission-99-r1100gs.749085/page-4
User TXJames over there did this fix to his own transmission, but ended up selling the bike a few years later and was unable to do a follow-up evaluation. He repeats the same result of increased transmission noise.
The shim to replace the wave washer is much less expensive than the new gear part (I have found a possible one-time source for both at $23 and $235 respectively); however, I can't find any long-term follow-ups from him on this, or any info on whether anyone else has tried it with successful results far down the road.
What I would like to know is if anybody has any experience with the wave washer replacement fix, and whether it is sufficient on its own to solve the input shaft wear issue while retaining the original chamfered gear design.
This is about the known issue with M97 Oilhead transmissions where the input shaft gear eats its way into the adjacent bearing on the rear of the input shaft, documented by Anton Largiader here: http://largiader.com/tech/oiltrans/m97.html
Anton, on his website, details the updated gear part with a larger surface area and no internal chamfer as fixing the problem. Unfortunately, this part is very expensive (currently priced by BMW, the only reliable source, at $330, plus shipping, plus tax, plus waiting-a-month-for-shipping).
I found this thread on the BMW Sport Touring forums from way back in the mid-2000's regarding this same issue, and an unorthodox (and much cheaper) attempt at solving it. https://www.bmwsporttouring.com/topic/13441-chocolate-gear-oil/
In this thread, user smiller details his attempted future-proofing: replacing the wave washer on the input shaft with a solid 3mm shim, at the expense of slightly more gearbox noise while in neutral. He theorizes that the spring tension of the wave washer allows a "hammering" effect where the gear repeatedly slams into the bearing when load is suddenly placed on the transmission, and that replacing it with a solid shim prevents this entirely. His reasoning is that the M94 input shaft had a very similar design but no wave washer and did not have this issue, and that the wave washer was only installed to quiet down the gearbox clatter while idling in neutral.
He also said he had done this fix to a couple of transmissions, including his own, that had failed input shaft bearings as part of rebuilds, and was planning to re-open his over 20,000 miles later in order to gauge whether it successfully prevented the wear problem. The only detriment to the fix was a significant increase in transmission noise in neutral but he considered this to be worth it.
Edit: Another transmission rebuild thread on ADVRider also mentions this solution with a nice picture: https://advrider.com/f/threads/i-took-apart-an-m97-transmission-99-r1100gs.749085/page-4
User TXJames over there did this fix to his own transmission, but ended up selling the bike a few years later and was unable to do a follow-up evaluation. He repeats the same result of increased transmission noise.
The shim to replace the wave washer is much less expensive than the new gear part (I have found a possible one-time source for both at $23 and $235 respectively); however, I can't find any long-term follow-ups from him on this, or any info on whether anyone else has tried it with successful results far down the road.
What I would like to know is if anybody has any experience with the wave washer replacement fix, and whether it is sufficient on its own to solve the input shaft wear issue while retaining the original chamfered gear design.
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