Clutch/primary noise??

I just finished restoring my 75 mk3. It looks great and runs beautifully. I notice a noise when the bike is cold while the rpms are still low from warming up. It sounds like a knock noise coming from the back of the primary or in the transmission. I used my long screwdriver to pin point its location and its most certainly not the engine. It can be felt also if I have my hand on the back of the primary cover or the trans. When I rev the bike I hear one slight clunk and with higher rpms it goes away. Once the bike has been ridden and warmed up, I cant hear a thing. Worry? or just ride the damn thing? Thanks

JD

You'd better watch out for the alternator rotor body coming loose from it's steel center. They can go away with horrid results.

Hi there , it coulpd be too the priming of your automatic chain tensionner not effective , it happens to me , when I had a MK3, and at that time it makes me frighten it was the bottom end going out .........so have a check also on that point , while looking at your rotor, just my two cents .
enjoy your summer Pierre

The MkIII has the hydraulic primary tensioner, and as marinatlas has said, it takes a while to prime after starting up, which can result in some rather serious sounding clunking noises until enough oil has been flung into the tensioner hopper by the primary chain for the tensioner to re-prime itself, and the noise then stops. Using thin oil in the MkIII primary like ATF doesn't help, although it's fine for the earlier models, as I found the tensioner works better with engine oil in the primary, and not ATF.

Thanks for the help. I'll check on the alternator and will also change the fluid from atf to engine oil. Cheers.
JD

JD,
Had this exact same situation on an 850 Mk2. Turned out to be a small part of the bottom of the primary chain case and top of the header pipe contacting intermittently under low revs.

Crouch down and use a flashlight and you may see it. Solution for us was to slacken the header ring and the muffler mounting plate, wedge a thick screwdriver between the pipe and underside of the primary case and tighten up the header ring and muffler mounting. Problem went away.

Mick