Thread: Piston clearance??

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So, I started with a .030 over 509 block 400 with a good bit of wear, and I really didn't want to go .060. So I did what everyone says not to do and bored it without having the pistons just to see if it would clean up before I bought the pistons. I bored it 4.163 which would be .038 over and it wasnt clean on three holes. So I ended up having to go dead on .040 over at 4.165 and two holes still had a small place at the very bottom where the bit didn't touch. I measured it and I could see where it didn't clean up but couldn't really measure it. So I got my neighbor (who owns the machine shop...he is in his 80's and retired) to measure it and he got the same results which was less than half a thousandth. So I bought a set of .040 keith black kb147's and thats as far as I got. That was in 2009. I just got back on it this week and as you can tell I havn't exactly been in a hurry. I measured the pistons last night and found that they measure 4.161, so with my block being 4.165 I have .004 clearance. Keith Black recommends .002-.0025 clearance for street applications so should I go ahead with the .004 clearance I have or do something different? Here is what gripes me....if I was going to design a piston that was meant to be installed in a .040 over 400 block, I would make them 4.063 which would give .002 clearance in a 4.065 block. Isn't that too simple?? My block wouldn't clean up on the .038 over that these pistons require, so what do I do now?