Metal porosity can be a real bitch. Once when I was racing I had a block bored .030 over. Everything checked out good so I put it together, started it, set the timing and let it warm completely up. I then shut it down to pull the valve covers & reset the valves. Got that done put the covers back on & went to start it again, it was locked up! I ended up tearing the heads off again to see what went wrong and I could not find a thing. Cleaned out all the cylinders so they were dry and went to check gaskets, came back & #3 cylinder had water in it! I wiped it out again then stood with a light right over the bore. All of a sudden a drop of water started forming on the cylinder wall. That engine was a running engine but when they bored it the hit a spot where there was just no material. The hole could not be seen either.
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