No compression in one cylinder

[kaw550]

A few weeks back I did a compression test and posted the results. They were fairly consistant except for one cylinder. It was below 30 psi

I pulled the head off tonight so I could see what the issue was. The cylinder looked fine. The valves were a pitted but I didnt see anything that would cause ther to be no compression. I tapped them with a hammer to confirm they still moved.

The gasket fell off when I lifted the head but there were no signs of a blown out gasket.

Any thoughts?

 

[360 4V]

How are the valve seats, are they sealing?

 

[Bronco717274]

From the looks of those valves it looks like your gasket was bad. Compression was going into your coolig system. What did that plug look like. You were getting water into that cylinder.

 

[Bronco717274]

PIc two you can see on right hand side where gasket was leaking between those two cylinders. Same thing in pic three right side of pic can see where it was leaking on head.

 

[kaw550]

So any way to tell if the block is worth saving or do I need to bring it to a machine shop?

I should have noted that it is out of a parts truck sat for over 10 years. I used mystery oil prior to starting
Here are the compression results I posted a while back.


Drivers side
Front
dry Oil
130 130
125 130
125 130
130 130

Passenger side
Front
120 150 (#1 Cylinder)
40 50
120 130
120 140

 

[360 4V]

I had to completely dismantle my engine and wash it redundantly before I completed my autopsy.

 

[Broncobowsher]

Pull the piston and see if the ring(s) are broken.

 

[360 4V]

Now that is an easy repair. Re-ring the pistons and hone the cylinders.

 

[broncnaz]

Block is probably still good need to have the cylinders miked to find out how much wear they have. its kinda hard to see how bad the scratches in cylinder walls are and how deep but I would say it will bore out to the next size no problem just honing and re-ring might not get the scratches out and if it does may leave you will a bore thats really to big.

 

[bluesbish]

only 30 psi is something major. remove the valves and look at the seats, if they look ok, I would look into scrubbed off cam lobe maybe. the cylinder and rings have to be pretty bad to lose that much compression. a broken ring will leave a line, scratch in the cylinder usually.

 

[Bronco717274]

Compression was going into water port you can see it from the pics. Head is probably warped I'd have it checked.

 

[360 4V]

Having a warped cylinder head is an exuse to have the cylinder heads milled.