Forum bmwbike.com

since you have swapped right hand side and left hand side barrels etc and the noise is still from right hand side I think you can disregard the barrels and pistons. To me it sounds like cylinder head. I do not know what you have had done to them but if you had new seats and valves put in make sure the collet holding the valve and spring is not hitting the valve guide. I have seen this twice now where people have had cylinder heads reconditioned and not done correctly. The noise sounds like a badly adjusted tappet - quiet loud. The solution is to grind off a small amoutn from the valve guide and replace the collet - but get a professional to do this. Hope this is your problem. Cheers Tom

UPDATE on rattling engien-one rod has play in it-the crank had only done 6000 miles from new-and ill probably need a new rear barrel roller bearing as well as the old one is impossible to get off the crank undamaged!

What did you find as the final problem/solution?

If I remember correctly from Kent's thread on other sites, he had installed a supposedly new factory crankshaft that he had bought from a dealer many years ago. Finally, Kent tore his engine down and found that this new crankshaft was defective - it had a bad big end bearing.

Thanks, I suspected a big end bearing as he reported the noise stayed on one side with the switch of piston/cylinder from side to side.

Could it be a broken valve guide? I had something like this happen on a BSA Gold Star once. The top of the valve guide sheared off flush with the head and produced quite an alarming rattle throughout the lower rev ranges as the loose ring of material bounced up and down the valve stem off the head and the valve collar. There again, it could also be excessive endfloat of a rocker arm. Or a worn small end bush. That can make quite a racket. When did you last clean out the sludge trap? You say that the motor hasn't been stripped since the 1970s.

PK