yes, another head gasket thread and mystery

[neo]

All,
I noticed some abnormal sound, or so I thought, this past saturday, that sounded somewhat familiar to the sound when the #1 cylinder exhibited a head gasket leak. Further investigation found light bubbles int he coolant when running, small little ones and an occasional burp of a slightly larger one about every 20 seconds or so. Broke out the handy dandy compression tester last evening and after removing about everythign from the passenger side, found these readings:
1: 380
2: 400
3: 400
4: 400
5: 400
6: 400
7: 350
8: 400

Is the culprit most likely cylinder 7? Could cylinder 1 be an issue too? At least both are on the same bank right? Any insight or other tests? I read about taking the t-stat out and belts off and trying to watch for which side the bubbles came from in order to help id the offending side.

Is there something likely I am doing wrong when putting the head back on that is contributing to the poor sealing?
This is on the 6.2 Bank TD mil-take-out engine I built for the wagoneer. It is runnign Mahle .030 pistons and full ballance/blueprint job wiht remaned heads.

Any advice (or a flamethrower) is appreciated.

Neo

[sctrailrider]

I would try the looking for bubbles in the crossover trick first...

[DmaxMaverick]

The water crossover trick is OK, but not necessarily the best method. Since you already have all the plugs out and it's accessible, apply some shop air to each cylinder (rotate crank to close that cylinder, and remove the oil filler cap). This will show which specific cylinder(s) is leaking, and you don't have to run the engine to do it.

[Robyn]

There is a good chance that you are dealing with a cracked head and not a gasket issue.

Give the shop air as Maverick mentioned a go, and then proceed.

The small cracks that form between the valves, can and do find there way far enough to allow leaks.

Once you narrow it down to which side is the culprit, get the head off, then look the gasket over well, and if it looks good, then have the head pressure tested.

Missy

[neo]

I tried the compressed air to the cylinder. Insured valves closed by putting on compression stroke a little before tdc on each cyl under test. No air escaping into crankcase, or none i could detect anyways. My compressor max pressure is 175 though, but i think that is 50 above most 2x7.5hp dual stage pumps.). I also check the radiator during this test and no bubbles from either one or seven. Cant run yet cause i had to take the turbo off to get to cyls 6&8. Rebuilding it while i can. I guess ill yank the head (again!) and see what i have. Pretty frustrated with it at this point, but guess it goes with territory. Ill update when head comes off. Thank you all veryuch for the input and advise. May try the tstat test one i get turbo rebuilt and back on.
Maybe a blessing. Have had turbo kit since christmas time when i did the burbs gm-8 and was wondering when i would get around to it. :D

[sctrailrider]

No need to wait till you put the turbo back on, just take the belt off, put the turbo oil line in the filler tube, remove the stats, crank her up and look for bubbles... don't let it run too long this way, it will heat up quick.....

[neo]

quick update. Head is off. Can't see anythign glaring on cyl 7 or 1 (slightly low) Head goes to shop in the am for the pressure testing to id any cracks and clean her up. Hopefully, it is okay. I'll post again once I know. Thanks again for all the help from everyone.