My name is Matt Morse,
I bought my CBR 900 RRjust a few months ago. The previous owner had just replaced the transmission before I bought the bike and now 1,000 miles later the exact same problems are re-occuring.
In Detail,the transmission began to jump out of gearat high RPM. At first, it happened every once and a while butthe problem quickly got much worse.
After dissassembling the exterior and interior shift mechanisms I discovered a damaged shift drum, left shift fork, and shift shaft (all of which had just been replaced 1,000 miles ago).The Left shift fork is rubbing against the sixth gear on the countershaft which has caused serious wear to the gear itself which was also brand new.
The previous owner had the exact same problem. He replaced the entire transmission and all damaged parts and it is re-occuring in exactly the same way, and damaging all the same parts.
During disassembly, I found no obvious mistakes in the re-assembly or any shady workmanship.
I found nothing wrong with the stopper arm or stopper arm spring which is the only other possibility the maintenance manual suggests.
I really haven't a clue as to what could be causing this and am very reluctant to re-assemble the bike with all new parts and without having really solved the problem because I knowI will be doing it all over again a month from now.
If anyone has any suggestions or information that could help it would be greatly appreciated!

Please and Thankyou,
M. Morse

 

I don't know enough about bikes to offer any advice here, hopefully this free bump will help though.

Sadly, it is pretty clear you bought someone else's problem.

If all else fails, take it to a certified Honda mechanic.