Low Compression on #3 and #4

[CharlieB]

My 76 1800 started running very rough several days ago, so I ran a compression test yesterday and came up with 130 psi on cylinder #1 and #2, #3 and #4 were only 30 psi (dry test). Wet test was still low on #3 and #4. Does this definitely mean the head gasket is blown, or could it be worse?
Not sure if it was necessary or useful, but I ran a separate test on #4 with a plug screwed in to #3. No change in results.

[vandor]

A leakdown test may tell you more, but it sounds like you will have to open it up no matter what.

[707kevin]

I thought I remembered someone else having similar issue recently and the head gasket between #3 and #4 blow out so neither would build pressure. that would be an easy fix anyways, lets hope!

[ebrown0104]

I just did a compression and leakdown test on my engine last week, and I ended up with decent compression on all 4 cylinders (120-140) but I had 70-80% leakdown on cylinders 2 and 3 (1 and 4 were 15-20%). So, there's a good chance you're gonna need a head gasket. I plan on driving my car until this winter and then tearing it down.

[CharlieB]

Thanks for the responses. I hope to do the leakdown test today. We had terrible storms last night so after the clean up I'll do the test and post results.

[So Cal Mark]

be aware that driving with a head gasket blown can destroy the block where the combustion gasses travel between cylinders