Frank: I agree with your specs, but we all know that has been exceeded many times over. What i am attempting to do here is get handle on the problem so that we can safely say. Dont worry about it or you may have problems. I am sure there are many heads out there that have been machined several times. How would you know without special equiptment? Using Bill's measurements, i can see how a replacement piston,connecting rod, head gasket thickness or a cam change could make a big difference. This does'nt consider how many times the head was machined. My point is the clearance that tight to begin with? I dont know.