Thread: Zero compression....

So I bought a DET from a friend of mine. Was told it had 10k on a rebuild and it ran.It has cometic HG, ARP studs and fresh beaings. Installed it into my car and started it. It was only running on 3 cylinders. Hooked up my scan tool and did a power balance test. Found #4 was not firing. Pulled the plugs and sure enough the plug looked brand new. Checked injectors and spark and they are good. Did a compression test and it showed (from 1-4) 155-154-152-0. Hooked up my leak down tester and checked for leaks and all the air was coming from the breather. Thinking the only way that could happen was a hole in the piston. Pulled the head and the piston VISIBLY looks good. There are no holes or cracks or anything. The only thing I can see on the piston as far as markings that shouldnt be there are what appear to be 2 small marks that look like that both valves some how hit, they are very very slight marks. Even with cracked rings, it should be giving SOME compression, and there is none.

Anyone have any ideas?

a hole in the piston would be very very visible lol. if the piston looks good it probably is, small valve contact marks arent a big deal, just polish them out a little bit.

sticking valve?

Yeah, if everything else checks out then I would say valve issue. Maybe it's sticking and not seating properly. That valve contact on the piston may have been just enough to warp the valves just slightly and cause them not to seat right and seal the combustion chamber. If that's the case then easy fix hopefully. Since the head is already off.

yeah it could be extremely bad valve or definitly a valve problem if there isnt a hole in the piston lol

Even then I don't see how it could show 0 compression. Definately interested in how this turns out.

could have been a leaking headgasket too, that might cause this issue

There might be an issue with the piston you can't see, especially on the sides. If it's leaking out through the crankcase it's definitely something to do with the piston. Kinda wondering how some people are thinking it's a valve issue when the leakdown is showing it isnt

I've seen motors that give 0 compression due to problems with the piston you can't see until you disassemble. There might be scoring in the block as well compounding the problem. Check it all, thoroughly, but seems to me you're looking at taking #4 out.

Yeah I broke the ringlands on a piston and it had ~60psi. I still just don't see how a cylinder with 0 wouldn't have an obvious issue once apart.

broken gauge? lol jk take it apart and look at it

Yea the 0 compression is throwing me off too, it really threw me off when I pulled the head and there was nothing(no holes) to see. It can not be a problem in the head due to the results of the leak down tester, believe me I was hoping it was a valve issue. I will pull the piston an see, there could be a chunk missing on the side. It was at BDC when I removed the head and there was no scoring on the wall, so that was a good thing.