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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