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rootsman's picture
Joined: 03/17/2008
Posts: 4

Upon reassembling this R42 transmission, I noticed something peculiar about the 2nd gear dogs on the output shaft.
Second gear slides on the shaft (via the shifting fork), and engages 1st and 3rd gears via the dogs. The dogs are cut with a bevel (like most transmisions), presumably so the high side makes best contact and keeps the gears IN gear, and the lower cut side so the gears will disengage easier and cleaner.
What confuses me on this bike is this.....When the input shaft is driving the output shaft in 3rd gear, the contact looks correct. The higher cut of the bevel is making full contact with the input shaft 3rd gear. HOWEVER when 1st gear is engaged, and the input shaft is again driving the output shaft, the LOWER cut side of the dogs are making contact!
It sure seems like 1st gear would have a tendency to pop out of gear this way. The only theories I can think of to justify this, is that the factory was struggling with the bike popping into 1st from neutral unexpectedly, and this would make it harder to engage 1st as a safety feature. Or that 1st is dramatically lower a gear than 2nd, so this was BMW's attempt at a sort of grinding synchro gear.
Does anyone have experience with this situation?
I have some good JPEG fotos of the gear, and what I'm trying to describe. I can email them to anyone who could offer an educated opinion on whether I should worry or not. Let me know your email address, mine is socastevie'AT'
Noone I know has ever ridden this bike, so I'm hesitant to reassemble until I know it will work right.
Thanks in advance,