Do air-cooled 911s ever blow head gaskets?

[H.G.P.]

I read so much about broken head studs, but do air-cooled engines ever (if possible), blow a head gasket? (Or does something else just give way first?)

[asphaltgambler]

Everything else being equal, there is usually are contributing factor(s)

[Superman]

The answer is "not," for a very simple reason. Our engines do not have head gaskets per se. If the mating surfaces are not flat, or if the head studs are not torqued properly, or if they break, then compression gasses can pass between the cylinder top and the head. But if everything is working properly, those surfaces make an effective seal. I'm not sure why there are those little aluminum ring thingies between my cylinder tops and heads. Those two parts mate directly with each other, so I think of the sealing ring as useless. But then, I'm not a Porsche engineer.

[H.G.P.]

Originally posted by Superman
The answer is "not," for a very simple reason. Our engines do not have head gaskets per se. If the mating surfaces are not flat, or if the head studs are not torqued properly, or if they break, then compression gasses can pass between the cylinder top and the head. But if everything is working properly, those surfaces make an effective seal. I'm not sure why there are those little aluminum ring thingies between my cylinder tops and heads. Those two parts mate directly with each other, so I think of the sealing ring as useless. But then, I'm not a Porsche engineer.

It seems to me, that since I'm going to re-torque again Wayne"s 55 rebuild book), there's a reason, keep mating surfaces sealed?

Anderson's book pp. 68-69 shows two head gaskets, mine with a metal perforated diameter, and another type for different model that even uses a tubular spring.

[Superman]

Not sure what you're getting at HGP. When I rebuilt my engine, I carefully torqued them, then retorqued them almost immediately, then continued to retorque them until they were stable. That is, I did not back off the nuts, but I put a torque wrench on them to ensure they were torqued properly after a heat cycle or two, or twenty, or a hundred. Eventually, they stopped accepting movement, and all are at the proper spec.

I had a head stud fracture, but I had damaged heads on several cylinders, not just the one with the broken stud. I had them flycut.

When I assembled the engine, there is a sealing ring at the top of each cylinder. The sealing rings go into a recessed area at the tops of the cylinders. In other words, while they touch both the cylinder and the head, they do not get squished between those two parts. All 911 engines, as far as I know, basically use a metal-to-metal seal between the cylinder tops and the heads. There is no "head gasket" per se.

[beepbeep]

Turbos don't have any "head gaskets" as far as I remember. So there is no head-gasket that can leak....unfortunately there is "uneven mating surface problem"

It would be much easier if you could just change gaskets instead of having to fly-cut the heads.

[tsuter]

Just weld the head on..... you'll be fine.

[svandamme]

Originally posted by tsuter
Just weld the head on..... you'll be fine.

if i remember correctly .... Porsche did that ... electron beam welded the heads to the cylinders in a 935 or 956/962... not sure which one

[Nine9six]

Hey Superman,
Did you get your torque wrench calibrated between retorqueing? :-)

[Superman]

No. But I did take all three of my torque wrenches to the airport where the aviation mechanics have theirs checked out/certified. Mine were certifiable. Kinda like me.

Hey, I'm curious as to any other method of connecting the cylinder tops with heads. Has there ever been an air cooled 911 engine where the mating of these two parts was not metal-to-metal?

[sketchers356]

Originally posted by svandamme
if i remember correctly .... Porsche did that ... electron beam welded the heads to the cylinders in a 935 or 956/962... not sure which one

It was the 956/962. Although it could have been both, I dont know all to much about 935 engines.