Jumping out of gear

[hezzo]

Hi guys
my 1980 cbx1000z has started jumpig out of fourth gear when accelerating.Does anyone know a fix for this?
Thanks

[Will]

Never had it happen with a CBX, but I’ve had it happen on other bikes. The reason was the bikes were being drag raced and the shifters were abused. The cause – bent shift fork. The cure – take the transmission apart (no easy task) and repair/replace the bent forks.

[daves79x]

I'm fixing one right now that has no 4th gear. I'll let you know what I find. Yes the engine has to come out and cases split - but top end can stay on.

Dave

[hezzo]

Thanks,i'll wait and see what you find before i do mine

[piit]

Some years ago when I re-assempled my CBX engine first time I had the same issue. 4th gear jump out in approx. 3000rpm.
I realized that I was intalled the parts 7&17 in wrong position (attached picture). It was very easy to fix.
If you have not overhaued the engine is it possible that some parts would be worned in gearshift setup?
Would be worth to check this first to avoid split the cases, just drain some oil out and open the left cover.

-piit-

[NobleHops]

Some years ago when I re-assempled my CBX engine first time I had the same issue. 4th gear jump out in approx. 3000rpm.
I realized that I was intalled the parts 7&17 in wrong position (attached picture). It was very easy to fix.
If you have not overhaued the engine is it possible that some parts would be worned in gearshift setup?
Would be worth to check this first to avoid split the cases, just drain some oil out and open the left cover.
-piit-

Photo:

[daves79x]

Here's the deal on the engine I'm working on with no 4th gear: It took me a while to find exactly what was wrong, but 2 things (both related) were causing the problem. Upon a cursory inspection of the gears on the main and countershaft and the shift drum and forks, nothing was apparent. A closer look revealed that the center shift fork was badly grooved on the M4 gear side, and the matching M4 sliding gear was very badly worn where it engages the center shift fork. This wear resulted in the M4 gear no longer sliding far enough to engage the adjacent gear. Since individual forks and gears are NLA, I just put in a good used set of shift forks and both complete trans clusters. It's ready to go back together, once I make final checks on the gear orientation on the shafts and the shift fork placement. It's very easy to get either of those things wrong. I usually dry-fit the lower case back on with a couple of bolts, then install the shifter and run the transmission through all the gears up and down a few times to make sure all's well. Then final clean-up and seal the cases. I can only guess the cause of this problem as someone 'riding' the shift lever while in 4th, or 5th gear, causing the excess wear in that area.

Dave

[hezzo]

Thanks Dave,and everyone else who contributed to solving this problem.

[Cammer]

Very early 1979's were prone to this problem if I remember correctly. Charlie

[daves79x]

Very early '79s all had the $hit run out of them - that's why they had problems. Parts were all the same for the entire '79 production run. For '80 on up, they slightly changed the design of the shift forks to reduce wear in that area.

Dave