Exhaust gasket confusion

[OldTee]

The following pictures show leaking exhaust gaskets on an engine with only 400 miles. The gaskets came from the standard gasket set, the cylinders are new Mahle, the heat exchanges are two year old SSIs. New nuts torqued to 25NM. I don't understand why they leaked. Is there another type of gasket in use? Should I have the SSI's ground down. I can't detect any warping.

[cgarr]

Something is not flat. I would surface down the header flanges, or at least check them on a surface plate, it does not take very much to cause a leak.

[911 tweaks]

a wild ass guess here... is it possible to have 1 or 2 heads slightly "twisted" in its position on top of the cylinder ?? Or, did a previous owner of the heads have 1 or 2 of the heads exhaust port surface re faced , now possibly causing all 3 on one side of the engine not to be on the same plane ???
I hate to even bring up these guesses as it could be involved to fix, but I would guess that you have already checked the ssi's surface to be all on the same plane !!
Like Craig said above, it looks like it is a slight area on the shown ports... put 1 header on a flat plate and try to slip a feeler guage under the specific suspect areas. This will tell if all flanges are on the same plane and square.
Good luck here and I hope for the best for you !!
Bob

[lucittm]

Tee,
You mentioned that your cylinders are new Mahle. Possibly, do they have the relief cut in the exhaust port for the ring type exhaust seals rather than the flange type? If your heat exchange pipes have the raised surface that projects into the exhaust port, the round gasket goes over that raised area.

I can't tell from your pictures if the exhaust port is cut for the newer style seals. Here is a picture of mine for comparison. Here is a picture of the newer seal, it is P/N 930-111-223-00, the 993 seal is slightly larger (DAMHIKT) and that P/N is 993-111-195-00.



Maybe your cylinders or your pipes (or both) require the newer style seals.

Good Luck,
Mark

[356RS]

Each header pipe on the header system is able to be pulled up or down a few mm when bolting up to the heads. In other words the pipes are a little flexible. Even if the heads were not the same in length between intake & exhaust ports or even a little bit twisted as Bob said, but I don't think that can really happen, the header pipes will move a relocate. I would say the flange's on the headers are not flat. The two bolt holes always seem to get bent upward after a few R&R's of the headers. File the header flanges flat and change out the gaskets then you should be good to go.

[rsrmike]

It appears in the pictures that the exhaust gaskets could be upside down.

Typically they have a steel side, and a softer side, either aluminum or grayish material.

I believe the idea is to have disimilar metals against both the aluminum head, and stainless flange. I doubt the SSI flanges are warped personally, mild steel pre -75 headers? maybe

I would certainly check the flanges as described above but you would probably be fine with new gaskets oriented correctly.

Also, most importantly, I've found that using liberal amounts of a good antiseize lubricant on not only the threads, but the contact surface of the nuts as well and tightening them as much as you can without breaking the stud always results in no leaks.

Unless you are using all new studs, all new hardware, and mild steel flanges, the 25 nm is simply not sufficient in most cases, as it's too easy for the nuts to start to gall or bind making the actual torque on the flange much less then what the torque wrench measures. This principal is also what lead to angle torque head tightening procedures

A quick call to John Daniel at SSI should give some more insight if problems persist...

Good luck

[rsrmike]

looking at the pictures again, you appear to have reliefs in the heads for the slip in tubes, but your stud length suggests you are using flat flanges??

That will most likely add to your troubles, looks like you have the wrong set of headers for your cylinder heads...

[Steve@Rennsport]

Good input from everyone,....

I cannot tell from your pictures, but if your heads have the stepped outlet surface such as what Mark's heads look like, you must use the SSI's made for that application (3.2) which have the tubes extending slightly beyond the flanges and into the ports. Those use the O-ring type seals that sit in that "ledge".

[OldTee]

Mahle cylinders was a mind burp. Cylinders are not in the equation. The heads are 79SC standard. New studs. The idea about the gaskets sounds good. Back in the old days ... aircraft had copper sandwich gaskets that compressed when installed. Aircraft headers were always warping and you would take a hammer and hit the ends of the flanges to bend them down. This solved most problems. Would love to find some copper gaskets for the 911SC. Stainless is not an improvement IMHO.

[88911coupe]

Just got new gaskets for my 3.2 and they look like stainless on both sides, i.e. they look like the ones in the pic...are we supposed to have installed them one way or another? I don't recall either side looking different.
Old Tee, did yours look the same on both sides? The only thing I noticed was the metal was that there was a seam visible on one side which I think I had oriented towards the cylinder side.

[OldTee]

Yes same ones. I installed them with the seam side toward the SSI flange and the flat side toward the cylinder. Maybe this is wrong. Don't' know. My simple mind reasoned that the flat side would give better contact to the cylinder which you don't want to leak and cause erosion.

[88911coupe]

That sounds like what I should have done. I was surprised how good the old copper ones looked after I cleaned them up a bit...probably should have reused them!!

[Bob Goding]

Probably just add to the confusion, But--when I was working in General Aviation,[I am retired now] there evolved an exhaust gasket,originally for/by Continental
that absolutely eliminated the too common blown gasket.
I was working with a fleet of Lycoming powered helicopters and the gasket P/N is still in the old memory bank.
Lyc p/n is 77611----so I googled it and got Aircraft Spruce as follows.

BLO-PROOF EXHAUST GASKETS
These gaskets are manufactured in a 1-
piece design in 7/64" thick steel. They
have a split metal inner ring which provides
an absolute seal and they are guaranteed
not to blow off. Engine manufacturer’s parts.
Continental P/N 627429 for all A, C and E Series ..............................$9.00 Ea
Continental P/N 628260 for 0-470-R .................................................. $6.40 Ea
Lycoming P/N 77611 for 4 & 6 Cylinder Engines .............................. $6.80 Ea

I dont know if any of them will fit Porsche ,but the design is a total success.
Maybe someone has access to some for comparison ,
Be great if this was of some use .
Bob

[cgarr]

They are close Bob, but the holes are about one hole width off, these are off our O-200