Compression issues after head replacement - desperate help...

revlis240 · Post by **revlis240** » 26 Oct 2016, 00:29

Hey guys,
I am losing my mind on this. I had a small leak in the head gasket (it would leak coolant into the cylinder overnight) so I sent the car to a shop to have the job done. Long story short, they were taking far too long so I decided to get the car back to my garage to get it done. I ordered a rebuilt head from a company on eBay and got a new gasket set. Here is the problem:

After the job, the compression is kind of all over the place. I get anywhere from 85 to 120 psi, and oddly sometimes the same cylinder will read 90 and sometimes 120. This just makes no sense. I added a tea spoon of oil, no difference.

I checked the timing FOUR TIMES. Turned the crank 90 degrees past the park and the 90 CCW. Tired also turning it 45 degrees past. All the marks line up. So I thought ok, let me remove the cams entirely as this should return all valves to their natural closed state right?

Well now I am lucky get 30psi on any cylinder with the cams removed. How the heck does that make any sense?

This car defies everything I know about how an engine works and I am losing my mind. I think I got a bad head from the rebuilder, but that doesnt explain the LOWER compression with the cams removed?

HELP. 2005 S40 T5

Post by **JDS60R** » 26 Oct 2016, 12:46

Start with a different compression gauge. This will tell us if yours is bad. If the hose leaks near the spark plug hole you will get crazy readings and never hear it leak.

If your gauge and second gauge match.
Then do a leakdown test to find the leaks.

Post by **alschnertz** » 26 Oct 2016, 14:41

I agree with trying a different compression gauge.

If you've removed the cams and the valves are closed, how will the cylinders get air in them to give an accurate reading?

Did you try to run the engine?

revlis240 · Post by **revlis240** » 27 Oct 2016, 11:06

With the cams removed I used the starter to turn the engine a few revolutions. Wouldn't that compress the air already in the Cylinder and give me a compression reading?

FREEBUSINESSES · Post by **FREEBUSINESSES** » 11 Oct 2020, 15:43

Why don't forum users ever post their solutions to help others with same issues. It makes no sense that people present an issue, then disappear.

Post by **volvolugnut** » 11 Oct 2020, 16:52

revlis240 wrote: ↑27 Oct 2016, 11:06 With the cams removed I used the starter to turn the engine a few revolutions. Wouldn't that compress the air already in the Cylinder and give me a compression reading?

To get a reliable reading on the compression test you would need all the valves operating during the test. The intake valves have to open to get air freely into the cylinder and then they need to close at the proper time in the cycle. With the intake valves closed, the piston will just make a vacuum on the down stroke and then compress back to near the starting pressure. Any leak at the valves or rings may let some air enter the cylinder and then you compressed the partial cylinder fill.

volvolugnut