Who wants to play "guess why this cylinder has no compression?"

[bryantreams]

Alright folks, bit of a sad day for me. Pulled out of a parking lot somewhat quick and a new noise came from my engine compartment. Sounded like an exhaust leak. Limped her home where I was already planning on swapping spark plugs and doing a compression test while I was at it. Here are the results
Cylinder-psi
1-135
2-145
3-135
4-0 (zero)
5-135
6-115
7-135
8-120


Cylinder 4 spark plug was oil fouled but not physically damaged.
Waiting to do a leakdown test tomorrow so I thought I'd post this to see if anyone cared to guess what's up with it. At this point I'm bummed out a little but have already started searching for a 454 to throw in her.

[bryantreams]

Btw all psi numbers are rounded to the nearest mark on the gauge so they're give or take 2 psi.

[BMERDOC]

I'll play! Given that the plug was oil fouled and there was 0 psi I'd say its piston/rings related. Maybe a cracked piston or a ring land broken . The exhaust sound is compression being lost through the crack or missing chunk.

[J Knight]

I'll guess bad exhaust valve, stuck open or bent.

[gmachinz]

I'll say cracked compression ring....the lower rings are prolly worn pretty good so oil is getting by them and past the compression ring to foul that plug.

[mrolds88]

With the oil fouling on the plug and no compression, I think maybe a couple of issues. Cylinder could have been gas washed and took out the rings. That would still give some compression, while giving that hiss. With the oil fouling, maybe the exhaust valve has gotten some buildup of carbon. This would not let the valve seat properly and not allow compression. My first thing would be to pull the valve cover and loosen both rockers on that cylinder. using one of those air chucks that screws into the spark plug hole put the air to it. That will tell you where your problem is.

[85Bowtie]

I would think it's more related to your exhaust valve than a ring issue. Even with a broken ring you should read "some" amount of pressure, instead it's going in and coming right back out from the way it looks. A bent valve could have damaged the guide/seal and that's where your oil came from. Doubt it's a ring, but that's my 0.02$

[Blackpony]

pull the passenger side valve cover and check the rocker arms.. also removing them will make it easier to do a leak down test.

[willett]

I'm with 85bowtie. Even if a ring is complety toast there still should be some pressure.

[bryantreams]

Ok folks, drove it to work today and ran the leakdown test vfirst thing. Had air coming out of the carb all the way through the cycle so I popped the valve cover off. The internals of this engine are completely unknown to me as the p.o. couldn't tell me anything about it because his brother built it so I don't know if I'm working withwith hydraulic or solid lifters. All the valves have some lash except #4 intake valve so I back off the rocker nut until it does. I hook the hose back up to the engine and shoot some air to it and it tries to turn the engine over. Then I put the Schrader valve back in the compression gauge and crank her over. 120 psi and it's pretty much cold at this point.


Two questions:

1. So in this situation would you adjust the valves, run the engine and pull the plug to see if it's getting oil fouled?
2. How do I know how to adjust my valves without knowing what kind of lifters I have?

[crashz]

Sounds as if the lifter might be messed up? It was running fine, then lost all compression, and assuming that the lifter was pumped up so much that it was keeping the intake valve open, it produced the loss of compression.

Solid lifters would not do this. If anything, they would simply rattle more and more as the lash built up. Same thing with bent push rods.

[bnoon]

My guess is that this rocker was too tight after the last reassembly and it finally damaged the lifter causing it to stick. I'm with crashz.

As for not knowing what lifters you have, you will soon find out as you pull the intake manifold to fix it.