Typical compression test numbers with blown headgasket?

[325DR]

I compression tested my motor and found two bad holes. All bumped to 95-100 on the first stroke, then maxed out in the 130-140 range. One hole went to 55 then 70. The bad one went to 30 then 35.

I pulled the heads and they were all blown. The cylinders that leaked the most looked like the gasket was barely blown. Two of the good testing cylinders had a completely blown out gasket.

So I had the heads vaccum tested and all valves are seating fine. They are o-ringed and when we pulled the gasket the o-ring was not compressing in the correct place. So we are giong to mill the orings out and use a thicker gasket.

So since the heads looked ok, I pulled the piston from the bad cylinder, and everything looks great. Rings float in the ring lands nice, piston floats on the pin nice. No signs of heat or cylinder wall damage. Ring lands look great. The shortblock was freshend 3k miles ago.

So my question is this: since the headgasket was blown on the bad cylinders, even though it was very very slightly, would that be enough to cause it to test so low? I am using factory GM head gaskets if it matters.

Thanks guys.

 

[TurboGN]

I compression tested my motor and found two bad holes. All bumped to 95-100 on the first stroke, then maxed out in the 130-140 range. One hole went to 55 then 70. The bad one went to 30 then 35.

I pulled the heads and they were all blown. The cylinders that leaked the most looked like the gasket was barely blown. Two of the good testing cylinders had a completely blown out gasket.

So I had the heads vaccum tested and all valves are seating fine. They are o-ringed and when we pulled the gasket the o-ring was not compressing in the correct place. So we are giong to mill the orings out and use a thicker gasket.

So since the heads looked ok, I pulled the piston from the bad cylinder, and everything looks great. Rings float in the ring lands nice, piston floats on the pin nice. No signs of heat or cylinder wall damage. Ring lands look great. The shortblock was freshend 3k miles ago.

So my question is this: since the headgasket was blown on the bad cylinders, even though it was very very slightly, would that be enough to cause it to test so low? I am using factory GM head gaskets if it matters.

Thanks guys.

Man, those are some strange Compression readings. Mine have been 0# for cylinders with blown gasket seal rings. I believe the slightly blown gaskets would be enough to result in low compression readings. Factory GM head gaskets are not made for o-ringed heads. Your solution of milling away the o-ring and installing a thicker gasket should work. However, you may want to simply use gaskets made for the o-ringed heads. Either way, the heads should be milled, at least slightly, to assure flatness. Good luck!