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Originally Posted by HSSS427
I then removed the intake and valve train and filled the water jackets on the head as high as possible to see if there were any obvious leaks into the intake or exhaust ports on the head. Nothing obvious spoted.
I then ran a leak down test on #2 with cylinder head at TDC - leak down passed. I then ran it again, with the cylinder head at bottom of the stroke and got air bubbles appearing in the water jacket openings.
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This tells it all. Valves closed by no valve train. Air from cylinder gets into water jacket when piston is BDC, but not when piston is TDC. The problem is not the head or head gasket or it would do it TDC as well. The only explanation is that the piston at TDC is covering and sealing the leak. This means that the cylinder wall is cracked into the water jacket some where bellow TDC.
Too bad you didn't start with piston at TDC and slowly move it down until the bubbles were seen. This would have told you exactly where to look in the bore. Keep checking that bore. There has to be a crack or pin hole somewhere.