After 11 years and 33k+ miles and hundreds of drag races it is finally time to replace the shift drum, shaft and all 3 shift forks. I had the occasional missed shift from 1st to 2nd the past 2 years that got more frequent towards the end of last year. Only had my bike out for about a month and 4 races this year and the problem keep getting worse until finally yesterday it would not stay in second gear under power at high rpms.

Pulled it apart today and removed the oil pan to get a look at the drum and immediately noticed it was badly worn. Went ahead and removed the entire clutch so I could remove the shaft, shift forks and the drum. When the shift forks were removed it was clear the left fork was badly worn and well below spec. The other 2 forks looked ok but barely measured above spec and showed early signs of rub marks. The shaft that holds the forks also measured below spec and needed replaced.

I was worried it may require new gears in the transmission but on inspection of the dogs on second gear they showed a little wear but still had squared edges on the dogs. If after replacing the drum and forks I continue to have the shifting problem I will replace the gears with new undercut gears but hopefully that will not be needed.

 

Will be following, would you mind taking some comparison pictures between the good drum and the bad one, also for the forks.

I saw the pictures and I can't tell what's wrong with the parts and I would like to have a reference when the time comes to replace them.

If you happened to have time, would you mind documenting the assembly (some pictures), thanks so much, been learning so much from reading these forums.

 

There's a **** on the end of that fork that sits in the groves on the drum. Look at the edge of the groove on the drum.

See how there are parts of it that are gone? Worn smooth? When you shift, the shift spline moves the drum, which moves the forks, and pushes/moves apart the cogs in the transmission.

You can see what the hard shifting has done to that drum. And it would explain occasionally missing a shift. Especially a hard/quick shift (which is basically every shift during a drag race).

On the shift fork, they ride in between the cogs on the input and counter shafts. They push cogs apart and together when the transmission loses it's load momentarily (either blipping the throttle or pulling the clutch) which is what makes you change gears.

You can see the wear grooves on those forks, they're VERY deep at the top of where it sits on the countershaft. The drum moves that fork a little bit, and the fork pushes on one of the cogs and slides it into the next position when you change gears. Those grooves are formed from the cogs still spinning very fast while the fork is starting to put pressure on it, either from full throttle/high speed shifts, quick shifts, or loading the shift lever.

It's amazingly simple how a transmission works... but it only works when there is no load on the cogs (otherwise they don't interlock and you don't change gears). So when either of those start to wear (the fork and drum), it, over time, makes each other a little bit worse.


You can see it going a fresh drum and forks going together here:

https://cbrforum.com/forum/street-fi...127508/page11/

 

Indian head shellac is amazing lol, but was wondering why you used it on the bearing surfaces? I've never messed with a trans like that.

 

It's not all Indian Head. If you look closely you can see the difference in color. The bright red is assembly lube. Indian head is the brown on the edges of the case. I was quite liberal with the assembly lube because I was spinning the motor by hand once I got it together. I just picked a few pictures that showed the transmission part so you could see how it went together and *vaguely* see what a good condition one looked like. The full motor build is in that that thread I linked.

 

Wow,thanks Mr Conrice, that was a broad explanation, thanks.

Now I understand why a missed shift or lazy shifting is so bad to the transmission.

 

Quick question regarding tools needed to do a proper trans or engine rebuild on these bikes. Which clutch center holder would you recommend? Any other random tool recommendations that make a difference would help. Thanks guys.

 

An air wrench...

 

Have one just not the large capacity compressor to go with it.. Seriously did you guys just buy the Honda center holder or a commercially available alternative?

 

Air wrench works fine. EBC makes an holder that you can get from ebay or if you change the clutch plates you can make one from them but you really don't need any holder if you have air wrench.

EBC Clutch Removal Tool Fits 02-03 Honda CBR954RR | eBay