Oil clearances and a surprise

Question: What clearance did you want? I have never heard that polishing would make things particularly out of round and have polished to get an extra .0005" clearance when I wanted. Besides, a turned crank is going to have a tolerance on the roundness that is something other than .0000". I personally would not be bothered with what you have, but don't know the application that you intend. (I've raced a couple of 4 cylinder rally car engine types with those clearances for 1000's of miles turning 6500-8000+ with nary an issue, but they weren't SBM's....)

Switch to synthetic oil after a reasonable break-in and don't worry about it if you are turning in the 1-1.2 HP per ci.....the protection that synthetics offers to bearings is pretty amazing.

Is there a reason to run the full groove mains here?