leakdown air from between cyl and head

[mskala]

I'm confused. Backstory will be farther down, but I did a leakdown and only
#6 cylinder was about 45%. No air from intake or exhaust but definitely under
the car. After engine is out (2.2 but with JE pistons, AA 86mm Biral cylinders) I
find no broken rings or scored cylinder. Re-bolt down heads and put leakdown
tester back on, and the air is coming from the bottom side of where the head
and cylinder meet.

I had cleaned the mating surface of the heads, there doesn't seem to be any
damage and these were done by a reputable shop only a few thousand miles
ago.

Right before this happened, I was doing an autocross and lost the fuel pump
(carbs) during a run, so for 30 seconds or so it was acting weird, likely getting
leaner and leaner while I'm still going full throttle. After fixing electrical issue
with fuel pump, I did a bunch more runs but seemed to be running a bit poorly
going home.

Not sure where to go next to isolate why the head is not mating up properly
any more, or if i'm doing something wrong.

[jpnovak]

few Thousand miles?

Check head stud torque. Could be loose or pulled stud from 2.2 Mg case.

[mskala]

There didn't seem to be any loose nuts when disassembling. I've temporarily
re-installed on the bench and torqued to 20. The studs are still all the same
length so not pulled. I put this together, heads were newly done, last year. Now
has 8K miles on it. Very strange.

[Steve@Rennsport]

Did your shop resurface the heads when they were rebuilt?

[mskala]

Yes, they were resurfaced.
It's hard to see but this is my pic of mainly #6. I used carb cleaner on the mating
surface and it seems normal I can still see the machining marks all the way around.

[mskala]

Well just trying things, and I swapped cylinder and piston #6 with #5. Now, the
leak is in #5, and #6 doesn't leak. So I think that eliminates the heads and points
to something about the one cylinder. Of course I also just realized that I was test
assembling with the old kinda beat up copper base rings, and just for diagnosis I
can try putting it together without any base rings and try again.

[911pcars]

Suspect, then measure cylinder height. You seemed to isolate this when you swapped cylinder positions (6>5) and observed the same symptom.

Sherwood

[kwikt 911]

Was your head gasket crumbled when disassembled?

[BK911]

I had air leaking there also on a 3.0.
I was able to lap the head and cylinder and issue went away.
Good luck!!