Quote:
Originally Posted by DrFerry
Could there be a different reason why nearly 100% of the blown S65s coming your way - with rod bearings greater than stock clearance - are blowing up? In other words correlation is not necessarily causation. Example: stock engines with stock OEM bearing clearances also blow up - and most S65 engines have already had the rod bearings replaced with a well known solution i.e. extra clearance bearings which increases the probability that the population of engines you receive will have extra clearance bearings.
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Without question, there absolutely can be other explanations. Interestingly, however, we have had a couple of examples of S65 rebuilds where the motor did not blow, but was rebuilt because approaching 200k miles, and rod bearings had been replaced with BMW bearings with the stock clearances. Fascinating for us and definitely contributes to our perception here. I will also say another principal BMW S65 builder's experience supports the conclusion in the race context.
But there is no way to draw any overarching conclusion even from a couple years' worth of sampling the engines we see. The chance of a skewed population is WAY too high for that. But the SRD gears DO increase oil pressure and, thus, by our lights, are a good precautionary measure at the very least.
--Peter