Tuesday, April 19, 2011

Everything's apart

Work continues on the CBR900RR transmission.

I got everything apart yesterday and had a chance to examine and compare the wear between old and new parts. It became very clear why the transmission popped out of second all the time. I guess this is all common for CBR900RR's of this era, and I believe you can buy "race" transmissions with custom shift drums and undercut gears. I don't have that much steeze, so I'll be replacing all of these with used parts.

Damage to the shift drum. When your foot moves the shift lever, this drum rotates and the shift forks follow in those grooves. The little peak there has some damage - likely caused by the shift fork slamming into it after 2nd gear popped out.

 Here's a picture of the dogs on second gear. Sorry the picture is so awful. I was taking it apart to do a side-by side, and I ran into about a dozen circlips and decided it wasn't worth my effort.

Either way, there's a raised portion in the middle of the photo. It should be perfectly square, but it's rounded off. That's why it would pop out of second.

And here's the shift fork. This damage probably happened first. It's about 3mm too thin, when means it would push the second gear cogs about 3mm short of full engagement. A few poor shifts and the dogs get a tiny bit rounded and it's all downhill from there.


  1. looks bad ,good luck fixing it love Honda CBR

  2. Aha! I believe the last time the prior owner replaced the second gear (with unworn square dogs), and the drum he said he did too, I'm quite sure he forgot to also replace the shift fork. I believe your theory is correct that the 3mm thin shift fork caused the new components to fail prematurely.

  3. Looks like you've got some hard work ahead! :x

  4. keep the updates coming, id love to see the end result

  5. you look like you know what youre doing. i hope you dont put too much money into the project

  6. These projects can cost a fortune.