Help with compression issues

[spencer_e30]

Hello, I'm trying to find out what is wrong with my compression issues. Just installed a fresh head gasket, timing belt, valve adjustment done, new head bolts. Not sure why my compression is reading so bad. Here are the numbers:
1. 150
2. 146
3. 90
4. 150
5. 125
6. 125

We're thinking it's probably a warped head. But would love to get other opinions as well. Thanks.

[digger]

Why did you need a new head gasket?

[spencer_e30]

The head gasket was leaking like a sieve. Not dripping on the ground, but leaking a decent amount once I cleaned the head. Gasket looked pretty shot once we got the head off as well.

[jlevie]

You should have taken the head to a shop to be checked for flatness and perhaps surfaced. Have a leak down test run. That will probably tell why cyl 3 is so far down.

[spencer_e30]

I'm thinking that might be our next step. It seems a bit weird to me that the ones directly around the 3rd aren't too bad. Could a warped head still bring those results?

[jlevie]

Yes, or it could be a problem with the valves. Pull the head and have a machine shop check it out.

[spencer_e30]

I'll have it looked at and will post results. Thank you for your help!

[TobyB]

3 suggestions-
lash the valves. Again if necessary.

run it a bit- like, take a trip to Rochester. Get it nice and warm. Take your AAA card.

then do a leakdown.

There are a lot of variables when the head's JUST been off- this will help reduce them.

And your numbers aren't 'deathly' bad, but I agree, something's not right. Or several somethings...

hth

t

[spencer_e30]

Thanks! Good ideas!

[zoomer]

Have you considered the piston rings?
Was there alot of crankcase ventilation before you removed the head?
Maybe the valves need to be resitted (try pouring some engine oil in 3rd cylinder and if the compression improves, this most likely mean that the valves are not sealing properly)
If the issue is with a wrapped head (I am surprised that you did not resurface it before install) you will be facing alot more issues than just low compression.

[ahlem]

If you put oil in the cylinder and the compression improves, it's the rings. If doesn't improve any or not much at all, it's the valves. If you rotate the motor by hand until the problem cylinder' valves are both closed, wiggle the rocker arms by hand and see if they show as much clearance as the others. You don't even need a feeler gauge to check this. If for some reason your intake valve isn't opening far enough, you will get low numbers.

[spencer_e30]

I'll try the oil in the cylinder. I have no clue why we didn't resurface the head especially after knowing it leaked from there. I'll post up some numbers if anything improves. Thanks again

[spencer_e30]

I believe we found the issue while adjusting the valves for the resurfacing. On the bad 3rd cylinder, the intake side valve wasn't closing fully and you could shine light through it. Then we figure the bad 5th and 6th is where the head is warped. So hopefully a resurfacing and a valve replacement solves it!