What do you do when 3 cylinders show 0 compression Chevy 350?

Answer 1

First I'd check valve adjustment, and the valves themselves to see if they are hanging open because they are either overtightened or damaged. Hopefully the problem is with the valvetrain because if it isn't, there is a good chance you have had a catastrophic engine failure, like holes in the pistons, a severely cracked block or cylinder head, etc. A bad head gasket is a possibility, but blown head gaskets rarely effect 3 cylinders (it's usually only one, or two adjacent cylinders) and rarely result in ZERO compression. The best case scenario would simply be overtightened valves because if no damage has been caused by them it's an easy fix that costs virtually nothing to fix. It is also the least likely culprit unless the valves were recently adjusted as a result of an engine rebuild or repair. If you (or someone else) just adjusted the valves due to repairs or a rebuild, it's definitely the first thing to check because it would be the most likely under those circumstances. Also check to make sure the camshaft is actually turning and opening/closing the valves. If it isn't, you will have at least three cylinders with valves hanging open, thus zero compression.