Topic: CB750 strange noise

[Lars]

This is about at 1977 Honda CB750 K7 - a never ending story. The bike is restored, engine by a good mechanich and the rest by me. On the first test ride, there were a noise from the clutcch/engine for a few seconds as I pulled off i 1. gear. Quite som rattle from the clutch, so I replaced the clutch fiber discs. There is still a lot of rattle  from the clutch, pulling the clutch lever and the engine runs nice. New primary chain and cam chain. All adjusted and synchronised. There ar e no marks, fine metals grinds inside the clutch house, everything looks fine. Got my engine mechanich to take out the engine and open the cases, to see if there are any issues inside, like the bears, bearing etc. on the shaft the clutch is connected to. Nothing to report so far. Anyone had any similar problems?

[flybackwards]

It seems that there can be many odd noises coming from clutch assemblies on these bikes. I had a similar story with my K7. After the rebuild I ended up replacing the stock clutch plate system with the 4 plate unit from Ken at CycleX.

http://www.cyclexchange.net/Engine%20Parts%20Clutches.htm

The result is a clutch which is quiet and shifts much better than the original. I will replace the unit on my K1 as well.

Some will also say to make very sure that everything is in tune and the carbs are properly synched to avoid any mechanical variations which can produce rattle.

Its worth a look.

[newday777]

If your carbs are out of synchronization the clutch will sound of a rattling noise. That noise is the primary chain slapping back and forth as the out of sync motor changes pressure on each piston.

[Maltboy]

If your carbs are out of synchronization the clutch will sound of a rattling noise. That noise is the primary chain slapping back and forth as the out of sync motor changes pressure on each piston.

+1

My 750's clutch chattered something fierce until the idle circuits were fixed and the carbs were synced.  One of the carbs had a partially clogged idle passage. It would allow flow, but not enough to keep the cylinder alive. This caused rough idle which made the clutch/primary chatter.  Drilled out the brass plug and cleaned the passage. It idles good now. Chatter almost gone.

[Lars]

I am aware of the adjusting and synch factors, so they are not the issue. Nothing obvious wrong inside the crank case after inspection, so the clutch is still in focus for trouble shoothing. I got info saying that the double steel clutch plate can be the problem, Honda's fix to that was install the GL1100 steel plate in the very bottom. This one is 1.6 times thicker than the original. You can still use the same springs. Maybe the 4 plate unit from CycleX is just as good a soulution, will look into that.