High crankcase pressure

[autox]

I have a 91 M42 that I've put a turbo on. Had a problem with smoke but found out it was the turbo seal leaking into the exhaust side.
I originally thought it was a head gasket so I got a .098 Cometic and ARP bolts, after install I had high crankcase pressure, oil bubbling out of the dip and oil mist coming out of the oil catch can breather. So I did it again this time using a OEM BMW head gasket, same results!!!
Compression's are 90,180,172,172
Any idea what else could cause this, pistons and cylinder walls look great...

[monty23psk]

are those numbers correct, your 90 cylinder looks to be shot. The other 3 look fine.

[colin86325]

Yep, probably the rings on the low cylinder.

[autox]

Your both are right...
I shot some oil in #1 and the compression jumped to 140, did it again with no oil and back to 90
Put some Lucas injector cleaner in for a overnight soak hoping it would free a ring up and it went up to 95
The cylinder walls are smooth with no lip still showing cross hatching.
Any ideas on what can be done besides a tear down?

[monty23psk]

could be a few things but only way to be certain is for a tear down plus that is the only way to fix this as well.

[jerseytim]

my car sucked up some ground and i suffered from all the rings being jammed in the pistons and even when the pistons were removed it was difficult to pull the rings out, the pistons needed heating up and it was worrying picking at the rings to get them out without snapping. once cleaned up everything went back together and worked fine but there was no way they were going to free themselves. the guy who did mine also skimmed the head to raise the compression and did it all in about 4 hours start to finish. good luck with yours and i hope it is an easy fix

[DesktopDave]

Motorcycle guys will use Marvel Mystery Oil or SeaFoam with thermal cycling to loosen up stuck rings. It works best on carb'ed engines. It also takes a long time. IMHO if the cylinder walls are glazed smooth the compression rings are worn out and you'll have too much blow-by for compression. You really have no option but to install new rings, have the block torn down & honed, and break it in gently. If you go that path and decide to skim the block be sure to assemble the front cam chain housing onto the block, or else the head won't sit flat during reassembly.