Doing a top end re-furb for a friend who says its a bit rattley. The valves and springs are like new, bit of wear on the guides. Bores glazed but OK and no wear obvious so were just honed. Both pistons compression ring gaps between .007 and .015". LH oil ring at .031 RH at .025. Bores at +.040".
Decision taken to fit new guides and new rings:- New bronze guides fitted, valve seats cut and re-ground-all good. Fitting new rings showed the problem. The LH piston was OK at '008 to .009" ring gaps but the RH rings would not fit into the cylinder??? Checking the pistons, which were a pair, showed the RH piston diameter (front to back) was .004" smaller than the left one. The RH ring gaps were ground on my Dremel to .009". Both piston to cylinder clearances are good at .005" each. I can only think this could be if the bores were machined to suit the individual pistons, what do you think. I have never heard of this before.
Anyway, it's all back together now and after 3-4 minutes running it seems OK except that the LH cylinder, which I consider to be the std +.040 size, is burning oil more than the RH one. Fingers crossed it will even out once the rings have done a bit of work. What do you think folks?