My green '71 B passed its smog test not long ago, but I got a
warning from the mechanic who twiddled it into submission that
the middle two cylinders were showing compression of 90 and 70
psi, instead of what they should show, up around 160 or so. Now,
I've known for years that the gasket was loose in the vicinity
of the #2 and #3 cylinders, because you can see that coolant and
oil seep ever so slowly from between the middle two spark plugs.
So a week or so ago I retrieved my head gasket set from Dick
Nyquist (who was holding it as a just-in-case spare while he
finished driver's school in a borrowed MGB) and over the past
few days I've taken a few swipes at installing it.
It's been an interesting experience so far. To begin with, all
the manifold studs stayed in the head when I took off the carbs
and exhaust. This is unique in my MG experience. Not only that,
but all the nuts were tight but required only a light tap with a
rubber mallet on the wrench to break them free. This scared me.
So last night, Chris Kantarjiev came by to help me wrestle the
almost 70 pounds of cast iron off the car. I got the ancillaries
off the right side of the head (air pump, air pump rail, heater
cable and heater hose), popped the valve cover, and we started
to loosen the head nuts.
After sweating, shoving, and struggling with my breaker bar with
a 1/2" drive, Chris and I stopped to catch our breath. "I'm really
really glad I don't collect stamps," I said. We went back to the
task and eventually got all the nuts loosened at least 1/4 turn.
To my utter amazement, all but one of the nuts came off the stud.
Only one stud screwed out of the block. This, in case you've never
done this, is virtually unheard of. Now, I had doused all the nuts
with Liquid Wrench the night before, but still, I had expected a
much higher stud count when all was said and done.
So with all the nuts off, we saw the head lift up slightly from
the block. Good, there'll be no problem getting the head to
separate. We pulled the rocker shaft so I could get the pushrods
out and ran into the first snag. The pushrod for the #3 exhaust
valve wouldn't come out of the head. It was being blocked in
by something fairly solid, so we just decided to lift the head
out with the pushrod in place and see what was what.
I pulled the head off of a slimy, oil-covered, coolant-spattered
head gasket -- of a kind I've never seen before, but had read about.
All the MGs whose heads I've pulled have had the fiber gasket with
a metallized top surface and rings around the cylinders; I've installed
copper-faced competition gaskets as well. But I've never before seen
the factory stock copper head gasket.
I suppose it could be a gasket replaced by an MG dealer at some time
in the car's life, but I strongly suspect that this was the original
gasket on my 21-year-old car.
Now, as for the reason for the low compression and also for the stuck
pushrod: You don't have to know what to look for to see what the
problem was. The big circles are obviously for the pistons, right?
Well, Mister Em Gee Buff, howcome you got three Os and one C there?
Yep... There's a section about 3/8" long missing from the circumference
of the gasket that goes around the #3 cylinder. It goes all the way
out to the pushrod hole for that cylinder's exhaust valve. Let's just
say that it's serious enough that I don't think my exhaust leak was
as bad as it sounded.
But discounting the cleanliness issues, the engine is in the best shape
of any MG motor I've disassembled. There is a ridge around the inside
of the cylinders where the top ring hits, but it's very minor compared
to the other two engines I've torn down. The cylinders are very smooth,
which unfortunately is NOT what you want; I can't see any crosshatching
lines, but the car does have 148,000 miles on it. And the blown gasket
on the pushrod side of the engine (the same side where the breathing
happens) explains why the engine was so heavily covered with gunk and
slime under the header and carbs. (I cleaned that off with Breeze and
a high-pressure water spray -- *before* I pulled the head, of course.)
The head looks fair too. The exhaust valves are a nice even brown, the
intakes slightly sooty -- I ran this car very rich for a long time. The
plugs (which are clearly not indexed, as Chris pointed out) show that the
smog dude got them right on the money; I'll try not to fiddle with the
carbs when I put them back on the car, but we do have a Colortune and I
now know the trick with the dashpot lifting pin.
So my current plan is to decoke the cylinder head and have it jet-washed
and probably resurfaced by the machine shop that did the machining for the
black car's motor, Kaeding Performance in Campbell. I really wish the
block were out of the car so they could resurface it and countersink
the stud holes... no, no, stop thinking that way. As I said to Chris
last night while I was talking about some other similar extension of
the work, "And all I ask is a tall ship, and a budget to build her by."
Kim had the best comment on the subject of rebuilding the rest of the
engine: "I won't let you do it. It's the beginning of summer, and this
is your only convertible. You'd be impossible to live with by June."
On the other hand, I'm almost certainly going to do *something* about
the roughness of the casting in the intake ports... and when the exhaust
ports clean up, I imagine they're just as bad. And the manifold really
needs to be ground off just inside the entrance, I'd bet... you get the
picture. No, dear, I won't rebuild it, not yet anyway.
In other interesting news, the cylinder head casting dates it at 2-71,
which fits well with the car's build date of March 1971 and the distributor
casting number saying that it was built in the 7th week of 1971, which
would be mid-February. Damn, a numbers-match MGB... does anyone care about
that kind of thing?
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