Compression=0...what would you do?

[o2batsea]

The good news is that repair for a bad valve or broken spring is pretty simple. A holey piston or busted rings on the other hand may be a death blow especially if the bore has scored beyond salvation.
You can still buy Bobeck's Iron Duke Chevy conversion that he pulled out of Red Square. It is a Robert Davis kit that was in there for only a year or so before he went with the 200tdi. Very low miles on it and a real improvement in performance. More or less a drop in replacement for the Rover lump.

[HybridIIA]

I'm not sure how well you could see the valve heads with the borescope, but I suspect you have a badly burnt valve.

[mongoswede]

Unless I missed reading it again: You could put an air line on the compression check hose and then put compressed air into the cylinder at TDC. If you hear air out the exhaust its an exhaust valve problem...intake = intake valve, air out the oil cap or PVC = rings. side of the block could be head gasket.

[I Leak Oil]

Zero compression should yield an obvious failure once the head is off. Even with a sligthly blown gasket or a sligthly burnt valve you should be getting a little compression reading with a standard compression test.

[bkreutz]

Since you've got the valve cover off.... measure the heights of the valves on #4 and compare that measurement with another cylinder. Make sure the rocker arms are loose when you measure them (rotate engine until you can "rattle" them. If the height is not the same I'd suspect a bent valve, even though you can see the valves move with a borescope, it's almost impossible to verify sealing using that method. It doesn't take much of incomplete valve sealing to cause this (another possibility is a burnt valve which would be hard to see unless the burnt spot aligned with your borescope). I think the next logical step is to take the head off and inspect, you've done about all you can do short of pulling the head.

[SafeAirOne]

If it was head gasket could it just impact one cyclinder?

Yes.

[LaneRover]

Is there oil in the coolant at all?

[Moat Creek]

Update on zero compression

Thanks all for your input an comments. I did a liitle work tonight and following are results.

1) I borrowed a fiber-optic borescope from work and checked cyclinder #4 which had the zero compression. From what I could see (2/3 of top) the piston has no holes and seems to move up and down freely when cycling starter. With the borescope I could also see both valves open in sequence with no sticking apparent. The valve heads look normal from the side view. I also looked at all the cyclinders and they seem consistent with #4. Piston crowns have some areas that are pretty rough and look like metal was splattered on them (all four)...not sure if this is normal or not.
2) I pulled valve cover and rotated engine by hand and then with starter and all rocker arms/valves seem to cycle as one would expect. No parts seem bent or damaged.
3) I rechecked compression and verified that #4 was still zero. I checked # 3 just to make sure gauge was working and it held at 150PSI and pressure did not degrade for the few minutes I was watching.
4) Not sure what the probelm could be other then crack in block or bad head gasket at this point. If it was head gasket could it just impact one cyclinder?

Anyway let me know what you think!

Eric

[mongoswede]

He did in the OP. That's the second number in his compression readings.

who reads the original post

[SafeAirOne]

Put a small squirt of oil into the cylinder and check the compression again.

He did in the OP. That's the second number in his compression readings.

[fubog]

I would remove the rocker cover and inspect the valve operation, as has been suggested, and (pending the results of the visual) set the bad cylinder at TDC compression and air it up. This is just a crude form of a leakdown test.
HTH
Glen in Fla.

[mongoswede]

Put a small squirt of oil into the cylinder and check the compression again. If the compression comes back its a sign that the rings are bad or not sealing. If there is no change then suspect valve train.

[Les Parker]

Could be a displaced push rod or valve tappet.
Remove the valve cover and have a look see.

[73series88]

yep gotta get that head off.
keep us updated
aaron

[SafeAirOne]

Eric,

I'd avoid replacing item after item till it's fixed. It may be a simple $200 (including parts) head job. It might be a whole new block. I'd suggest that you troubleshoot and identify the exact problem as described in a few of the other posts. That way you'll know if you're in for a simple, fast and cheap fix or whether the engine is toast.



Just trying to run through scenarios where compression would equal zero on one cylinder...

Valve stuck wide open

Piston not moving at all

Large hole in cylinder wall/block

Large hole in piston


I can't think of any more off the top of my head. I'd think that without any rings installed you'd still get some sort of reading on the compression tester.