Unexplained rattle - any ideas?

Hi Folks

Took my â58 Model 99 for its MOT at the weekend, a run out of ten miles or so. After a couple of miles a disconcerting noise appeared, metallic like a marble being thrown around in a biscuit tin, and seemingly responding to the road surface â that is, the rougher the road the more rattley it became. Just at the point when I was thinking I should stop to investigate, it disappeared, and I continued on to my destination.

The bike passed itâs MOT and armed with a new certificate and the feeling of rejuvenation one gets on these occasions I decided to go the long way home, taking in forty miles or so of green lanes, twisties and fast bits, at one point hitting 90mph on the old chronometric which I suspect in reality was more like 80. I had completely forgotten about the noise until just a few hundred yards from home, and going down a bumpy road, it came back again.

Now Iâve looked all over the bike and cannot find anything loose or missing. As the noise seemed to be coming from the left hand side I suspect something may be astray in the primary case. A few months ago I treated the bike to a new primary chain and whilst in there adjusted the clutch as well, a job I have done many times before. I have checked the chain through the inspection cover, at several points through itsâ run, and it is not too slack or hitting anything. I am wondering if the clutch adjuster locknut has vibrated loose, as I would imagine the chain picking it up and flinging it about could produce the sound Iâm hearing. If this is the case, I suppose I should count myself very lucky that it found somewhere to lodge safely whilst I was enjoying my spirited ride home.

Have any other members encountered this problem? The reason I ask is that being a boots and braces type of bloke I have virtually welded the two halves of the primary together with RTV, and it is going to be a time-consuming task to remove the outer cover. I would like to discount any other possibilities before I get the spanners out. I remember there being a witness mark on the inside of the outer cover when I had it apart, from where the adjuster was hitting it as the clutch was disengaged, so Iâm not even sure that there would be sufficient clearance for the locknut to fall off anyway. Also, I would expect the clutch action to be affected, but it is not.

I think it is inevitable and probably wise to get in there and have a look anyway, just want to be sure Iâve checked everything else before I do so. Any thoughts/comments/suggestions greatfully received.

Thanks in advance

Martin.