I left my car with a bmw mechanic for a personal opinion who acknowledged that my engine does sound surprisingly loud ie dieseling cold, comparatively speaking as we all know there is normal slap in these babies, and what might seem extra loud to the untrained ear. However, leakdown shows a very tight motor which has only 93k on it. In posting on several other boards, I learned from Mario of Vintage Motorsports that the factory clearence is a generous .0006 on the 80's era M engines, as they were built for heat and high rpm to never fail. Does anyone have experience with rebuilds using the MaxSil pistons that Bavarian Recycling uses on their rebuilds (or similar non-forged)? And if so, an appropriate clearence for these pistons in an M engine, which apparently expand much less than factory Mahle pistons of that era? Given that we are going into the off season, I am considering a bottom end rebuild, and believe, if we rip it apart, we may find oval cylinder bores. Also, what's the most these blocks can be overbored?

fwiw, my M5 with over 200k has no piston slap, What were the leakdown numbers if I may ask ?. Stock is 93.35 of course and the factory allows 93.8mm. I wouldn't want to go past that. There really isn't any point as the gain in engine size is nominal with a 84mm crank anyway. Do the math, it's dissapointing . I haven't used the Maxsil pisons, but have used other forged new technology pistons with good results

His leakdown just after purchasing about two mos ago like new, worst cylinder 6%. Ran low on oil during drive home 500 miles with it (quart and a half), so that does introduce possibility nothing got sprayed on walls while light was on (which I didn't see as block from steering wheel), and didn't check level upon leaving seller as he assured me it was all set. BMW Mechanic says that wasn't low enough to cause a problem. Thanks for your reply... I just left it with him today for a "diagnosis". He initially did tensioner to no improvement.

1.5 qts low won't cause the oil pressure light to come on. It would cause the oil level light to come on, but oil pressure should be sufficient

My mechanic came back with "totally normal sound for straight six bmw engines of that era". Even considering doing the bottom end would be a waist of time and money. Guess I will go ahead with some performance mods. Guess its not a bad thing to be overly cautious/concerned.