Originally Posted by tonysrep
I find it hard to beleive its your tranny with intermitent power loss at full throttle . If second gear broke there would be no gear in second period . As you can see the drum holds the shifter forks in place so they can't move from their programed position, it would not come and go. They usually also make a terrible noise when they let loose. The only other thing I can think of is missing teeth or melted teeth if it was the tranny but it would still make a hell of a racket IMHO
Tony, several VERY experienced technicians had exactly the same thoughts as you posted. The failure symptoms seem atypical for a transmission or gear failure. Also reproduced it on a dyno, where wind noise isn't an issue. Still couldn't hear grinding, but putting hand on transmission case during the problem indicated possible mechanical issue, sort of a "chunk" vibration.
Just to be clear: problem isn't intermittent in the sense of hard to reproduce -- it happens every single time those exact conditions are met: 2nd gear, high power, above about 8,000 rpm. Never, ever in any other gear. Power interruption is momentary (about 1/4 sec) but physically violent -- entire bike shakes from power disruption. Yet no audible grinding or high rpm as if slipping out of gear.
If you pin the throttle in 2nd, it always happens at least once between 8k and redline, sometimes 2-3 times. If you stay on the throttle (which takes some guts under those conditions), it pulls to redline.
At dealer's request, we tried many things to better understand problem, inc'l continuously applying shift pressure on shifter after reaching 2nd gear, put stock intake back on, etc. This resulted in many runs to reproduce the problem.
Toward the end of that day, problem seemed to be progressively getting worse, on the last run it happened at about 6k rpm at about 2/3 throttle. In hindsight, we were probably further damaging the transmission with each pass, but symptoms were so puzzling we (inc'l BMW) were unsure it was transmission, ignition, fueling, throttle butterflies, or something else.
Thanks for posting that picture. I'm going to the dealer to inspect the teardown tomorrow. Maybe I could take some comparative pictures.