need advice about compression test

[Tools R Us]

Ok, for some background-the head was checked and rebuilt about 2000 miles before the bottom end.

The valves were checked by the same shop that did the lower end.

I just bought a compression tester and had these terrible numbers:

1-150lb
2-170lb
3-60ish lb
4-30lb
5-15-20lb
6-30lb

At 4 I tried the oil on the piston trick to see if it would hold more pressure. It didn't.

Am I looking at a bad HG?

That type of result is almost always valve(s). To confirm; remove the plugs, bring the target cylinder to TDC/compression, pressurize with compressed air and listen where it comes out, intake, exhaust, other spark plug hole, oil cap or radiator bubbling, this will tell the story.

The "proper" tool for this is a leak down tester. I have one, somewhere, never use it, over complicated for the job, and the results are even more subjective than compression testing. The quick, dirty, , but effective way: Most compression testers have a hose that connects to the gauge with an air fitting, the spark plug fitting end has a schrader valve (like a tire) in it. Remove the valve, confirm the hose is free flowing, screw it into the spark plug hole, connect the air supply, and effective.

 

[69LC]

Thanks fir the suggestion. I'm actually on my way to borrow one from a coworker.

 

[dogfishlake]

I believe your head out of square dimension is beyond the maximum allowed in the fsm. It certainly sounds lime compression lost due to bad head gasked due to uneven head clamping. Could be wrong but sure sounds like it. Of course, you would likely see the other signs too like white exhaust smoke, water in oil, oil in coolant i suspect.

 

[69LC]

That's what seems odd. There was no white smoke, no obvious oil in the coolant. The machine shop called me today after I emailed them last night. I will check out the engine with the leak down test once I get ahold of the equipment.

 

[Tools R Us]

I believe your head out of square dimension is beyond the maximum allowed in the fsm. It certainly sounds lime compression lost due to bad head gasked due to uneven head clamping. Could be wrong but sure sounds like it. Of course, you would likely see the other signs too like white exhaust smoke, water in oil, oil in coolant i suspect.

If the head gasket were leaking, would expect coolant consumption. To have the leakage needed to cause that much compression loss, would be blowing coolant out.

 

[dogfishlake]

If the head gasket were leaking, would expect coolant consumption. To have the leakage needed to cause that much compression loss, would be blowing coolant out.

Good point.

 

[Irish Reiver]

If the head gasket were leaking, would expect coolant consumption. To have the leakage needed to cause that much compression loss, would be blowing coolant out.

Agreed but with 4 of the 6 cylinders at or below 60 I doubt if the engine would even have fired.