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I have a 1981 CB900 with the dual range trans. At idle it makes a light knocking sound that changes when I pull the clutch lever (put pressure on clutch plates) It almost goes completely away if I put the bike in gear and does go away when I start to let the lever out (more pressure on stuff).

I checked the clutch assembly and found no obvious problems, but chabed out the complete drum assembly, bearings, shims, Etc. anyway. SAME NOISE.

The noise must be transfering from somewhere else? Could this be the timing chain loose? Is it adjustable? The noise is more pronounced in the Trans. are than in the cylinder area.

Any help greatly appreciated!!
Thanks.

actually, my bike does the same thing..slight knock, but when you pull the clutch lever it goes away. captain obvious points to something dealing with the transmission as thats the purpose of the clutch...so i would guess something in that area. hopefully i dont seem to redundant, basically restating what your suspicion was...just validating. maybe a wrong oil viscosity? possibly just a 'honda thing'?...id like to know if anyone knows what the deal is. doesnt seem to affect it really, tho.

This is a common problem with a lot of bikes, and based on when it does it and when it does not, I think I may know what's wrong.

The clutch gear and its mating gear are probably straight cut. In order to take up some of the "slop" in the gearing, some makers install a thinner spring-loaded gear right next to one of the gears in question. The spring-loaded nature of the thinner gear allows it to take up the slop between the two larger gears. Occasionally, the springs in the thinner gear break or wear out and this slop is no longer taken up, thus causing the knocking sound you may be hearing.

Something else that can make the clutch noisy is if clutch basket wears. Basically, each plate has tabs which stick out round the plate, castle-like. These slip into slots in the clutch basket. These slots wear over the years on older bikes, so there is some lateral play in the plates. If this is the case, then replacing the clutch basket will reduce the noise. Also, as previously mentioned, replacing the springs will also help.

Cheers
S

What is a "dual range trans" on a CB900? I've heard of them for CT90's, but not a 4 cyl road burner.

sometimes synchronizing the carbs will stop the rattle at idle.

I had a 1981 CB750 with the same noise. It turned o ut to be the primary chain, it rattled at idle. The chain got really stretched aver a LOT of weelies and burnouts.