[Fot] mysterious low compression readings after initial break-in

[Greg Solow]

For the compression to drop from 210 psi to 90 psi, I would think that there is a pretty large leakage path.  You said that you had checked the cylinder leakage. Did you check it both cold after initial assembly and then hot after the cam break-in?  What were the numbers that you got. Again, I would expect the leakage when you have low compression to be extremely high in the cylinders with only 90 psi compression. 
       What is the top compression ring end gap that you are using?  What are the top rings made of?  different materials require more  or less end gap. If the ring gap is to low, the end of the top ring should show some signs of the ends touching one another. probably a polished surface compared to machine marks.  
       I would not expect that amount of  leakage that your engine is experiencing would be from a head gasket unless there were an open passage connecting cylinders 1 & 2 . 
       We recently had an MG-A engine  that a good machine shop had completed a valve grind on in the shop.  It showed 70% leakage out of one cylinder and 130 psi compression compared to 165 in the good cylinders. It turned out that the intake valve seat in the bad cylinder was not ground on the center line of the valve guide. I am not sure exactly how that happened but after we took the head apart, reground all of the valve seats, narrowed them to the proper width, check them with prussian blue, lapped them into each valve with fine lapping compound, the compression came up to 165 in all of the cylinders. The bottom end had about 25,000 mile on it and the cylinder leakage now varies from 5% to 9% in all of the cylinders. 

                                                                                                                Greg Solow
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