Transmission can't be fixed.

[sixtysix]

I got this via e-mail from a member 'Waldo' who is not able to post just yet ( I did tell him how) but I thought I would just post it anyway.

From Waldo:

May 26/03

I have a problem with my 1981 Yamaha XS1100 in that it developed a "skip" in second gear. It was "hopping" in and out of gear when I accelerated. My mechanic took the motor apart and sent the 2nd and 5th gear to a machine shop to have them "undercut". He then put the motor back together. Sorry to say, it wasn't fixed - same problem. He is now tearing the motor apart again to investigate. Could you offer some possible scenerios on why the problem still exists? I did have the second gear, fifth gear and shifter forks replaced once already. I have put 30,000 KM on the bike since they were replaced. I was under the impression that "undercutting" the gear would have corrected the problem on a more permanent basis. What could have happened?

[Snow]

I know that I know very little overall about these bikes, but I do have a couple ideas:
1. Perhaps the clutch is worn out? Right now, I am pretty sure my clutch is pretty worn and when I get in 3rd or 4th gear at very high rpms, it tends to skip a little and then settle back in and the rpms will come back down a little and the bike will pull harder again.

2. Perhaps he is making the mistake I made, running fully synthetic oil in a bike that cannot handle it?

3. Ok, this one is a bit dumb, but maybe the mechanic has been taking the wrong gears to the machine shop?

Just a couple speculations

[Dennyz]

There is more to the "second gear" problem then just the gears.

Most likely the shift cam and shift fork are damaged.

When the bike jumps out of gear it twists the shift fork, often bending it. This twisting force will eventually wear the shift cam slot out of spec.

[Mike Hart]

I agree with Denny, the shift drum can be worn out of spec without looking bad to the eye. Shift forks aren't all that pricey....

[Geezer]

I've seen this dozens of times on many different bikes and it's almost always 2nd gear (2nd takes the most abuse.)

1, look at the dogs on the gears, they probably have rounded corners or chunks out of them.

2, look at the shift forks, if the chrome has and wear through, or wear marks not on the fork ends, replace them.

3, Check the shifting drum and the pins that go through the shift forks into the drum groves. The drum is usually the last to die, but look for wear in the groves where it cams the shift forks. Also remove the shift forks even if they look good, if the pins have any perceivable wear, replace them.


Geezer