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Discussion Starter · #1 ·
Two years ago my friend and I rebuilt my 70’ CB450 engine with the bottom end of 68’ CL450. It was riding pretty well for about a year (for the exception of some power loss). But about a year ago I went for a ride and while riding in 5th on the highway, the whole bike jerked like the clutch slipped and caught several times. So I backed off and slowed down. I dropped into fourth and everything was fine. So I shifted back up into 5th and the same thing happened. I did not hear any knocking or metal crunching around in there.

Testing:
  • My friend, who is a mechanic, sent a camera into the engine and found no abnormal wear on the gears or the dogs.
  • I am still able to ride in 1st through 4th but 5th gear keeps slipping. Again, no knocking or strange noises.
  • I am currently working through all the options of what it could be. With the hope that it is not something deep in the gearbox like bent shifting forks or worn dogs.
  • I recently put the bike on the center stand. Started the bike and cycled through the gears. Every gear engages and the rear wheel will spin.
  • 5th gear does engage and spins when I hit the throttle.
  • It appears that when 5th gear is under load on the road it slips (again no knocking or strange noises).
I have made some repairs already.

Repairs:
  • I hoped the problem was the Gearshift drum center (which turned out to be fine) and the shifting pawl which was a little worse for wear.
  • So I replaced the detent roller, the whole arm, and gave it a new spring. Definitely shifts better now but same issue in 5th gear.
Theory:
  • Could this be a clutch issue?
  • The clutch plates and springs are all original and should probably be replaced regardless
  • Would a clutch adjustment also help the situation?
  • I really hope this is not an issue that would require me to split the case

Any Ideas or recommendations about the situation would be greatly appreciated!

Best,
Kevin


 

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Kevin - if the engagement dogs on the gears involving 5th were the problem with it "slipping", you would hear and feel nasty sounds as the dogs jumped out of engagement. If the engine revs up under acceleration load in 5th gear but it's a smooth increase in rpm with no nasty noises or "jumpy" feelings in the driveline, it's just a worn clutch that is slipping under the load of the highest gear ratio, which is why it does not slip under the load of the lower gears
 

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Discussion Starter · #3 ·
Thanks for your help, Tom. I'm going to start working on the clutch the next chance I get and I'll keep you posted on the progress.

Best,
Kevin
 

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The best way to test for the clutch slipping is to accelerate up in the rev range in 3rd gear, shift to 4th gear and (if you've ever powershifted in your life, you'll understand) make sure you bring the revs up high as you let the clutch out after the 3rd to 4th shift... if the clutch engagement doesn't immediately bring the revs back down to the appropriate level to continue further acceleration in 4th, but rather the revs stay up quite a bit and slowly come down as the clutch finishes engaging, that's clutch slippage.
 
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