Noise from the Primary Chain Case

Hello

I have a noise, (I would say a whining noise), from the primary chain case area. As background, the machine is a 1972 750, and an Alton starter is fitted. A couple of years ago, I did complete engine and gearbox rebuilds, and all bushes and bearings were replaced. The bike is running well.

The noise seems more apparent sometimes than others. I cannot say that the noise started following the rebuild; in fact I think it may have been around before that. The noise broadly follows engine revs, but varies significantly between power on and off, and is most prominent when cruising at low speed. I am not aware of it in top gear, but other noises take over at higher speed. I believe that I can hear it when the bike is stationary in neutral.

I have had the primary apart and I have replaced the primary chain with a double row chain from The Chain Man. There is quite a difference between the tight and loose spot on the chain, as there was with the old chain. I was hoping the new chain would address that! When setting the free play to 3/8” at the tight spot, there is maybe 5/8” at the loosest. Is that within an acceptable range, and is it enough to create the noise? There is no appreciable difference in the alternator gap as the crank is rotated, so the variation is caused by the clutch. I measured the runout on the mainshaft when everything was apart, and, given my fairly basic measuring tools, I could not detect anything. If that is correct, it points to a problem with basket. I cannot detect any play in the basket with the chain in place. The clutch itself is all original, apart from the addition of an extra plain plate. The plates are the Surflex type and do need cleaning from time to time to avoid slip, and would probably benefit from being replaced.

It looks like it all needs to come apart again, but is there anything else that I should be looking at?

All advice gratefully received.

Thanks

Ray

Be better moved to

I have a 1973 with an Alton. Here are some ideas.

It is a good step to eliminate parts of the clutch from this. Can you hear it at idle, stopped with clutch engaged in neutral and can you also hear it at idle, stopped and clutch disengaged and in first gear? I guess revving it up in both cases may help to hear it?

Have you tried using a piece of cut off garden hose as a stethoscope and listening to the outer chain case at the front side next to alternator and at the rear side next to clutch basket to see if you can isolate the sound? There is so much noise this may have no chance to work!! Maybe try listen from the side and then from the top of the inner primary case at front and rear above the alternator and then above e the clutch basket. I guess one person can rev the engine and the other play doctor with stethoscope!

Have you checked the primary chain alignment front to rear and shimmed behind the clutch basket as needed?
I don't know if misalignment would cause the noise but thought maybe check it

When you had it apart, was the Alton sprag ok and running very freely in one direction ?
(When it is next apart, you may want to clean out the sprag and degrease it, inspect it and if al ok, lightly with a non EP grease and reinstall. There is another
thread on the Sprag at this time. I learned a lot about sprags and picked up the right grease for less than $20 for a big tube)

The outer part of the Alton sprag rotates at engine speed and the inner does not. Maybe check to see if there is any interference caused by these two evidenced by marks. One would be interference between the assembles sprag and the other would be between the outer sprag section with gear teeth and where it is contained by the alternator.

Dennis