Dead cylinder!!!?

[Geoff87]

What are some of the possible causes of a dead cylinder? Bent valve, cracked valve, etc. I did a compression check on a motor in an '87 T on Sunday, and the #4 cylinder reads only 30~ PSI!! The rest were at 130#.

I'd also like to add, that this car has been sitting for the past 6 yrs or so. This T has 133K miles on it.

Am I correct in assuming that a valve is the culprit?

TIA!

 

[KEVINS]

blown head gasket... which may be why it's been sitting..?

 

[Geoff87]

Wouldn't there be oil in the coolant, or vice-versa?

Oil is clean, as is the coolant.

 

[Steve Wood]

not if it blew between cylinders.

Pull the valve cover and see if the valve is going up and down.

 

[Geoff87]

Thanks! I'll check it out.

 

[Geoff87]

Just wondering.....

I didn't have time to check if the valves are moving, but...

If the head gasket blew between cylinders, wouldn't there be two dead cylinders, instead of just one??

 

[TurboDave]

One of the more common head gasket "blow" methods is to go into the intake valley, or out the bottom of the cylinder toward the header. That will yield a dead cylinder and probably no oil in coolant, and no coolant in oil (unless it was bad enough to hit a steam hole).
If you had a valve hanging open I would think you wouldn't be able to see ANY compression. Same with a hole in the piston, NO compression.
But a blown headgasket will show some pressure if it's not too bad.

 

[Geoff87]

Okay, that makes sense.

Thanks Dave!