Larry,

I know one thing that has not been addressed on this board, is the optimum compression of the installed cork gasket. My guess is 20% compression.

If you, or someone else could supply the thickness of a new Porsche pan gasket, tonight I could measure the installed thickness of my 90'S4
original gasket and then compute percent compression that was applied at the factory. That should be a good measure of a good seal.

Barry
90' S4, Slate Metallic

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Barry,

Sorry in advance for this turning into a pan gasket diatribe.

The gasket provides three functions:

First it is a splash seal for flung oil assuming that there is basically no pressure in the pan. This also assumes that the pan is not overfilled and
that the capacity of the pan is the rest capacity of the system.

Second it provides an air seal to the engine as it runs under vacuum in the crankcase normally. Some engines false idle air this way when the breather
system is plugged. I know my Audi does this. I don't think that the LH or Motronics have this issue but it does happen. All depends where the fumes
are dumped into the intake. This is also especially important in evacuated dry sump systems.

Last it is a thermal break between the block and the air cooled pan. This is one of those extra little design features that separates our cars from the
rank and file of automotive engineering and is one example of the stuff I love about the car. It's actual contribution to overall cooling is most
likely small but it is the stuff that German car engineers worry about because their task is to design something that can go down the Autobahn with
the throttle mashed to the floor for hours!

On top of all that there is a torque spec for the 7mm? (10mm hex) diameter steel fastener that is in the manuals that is misleading because it is
actually for a metal to metal joint. This does not apply to a 3mm? cork gasketed joint. The actual torque spec should be tighten the bolts all hand
tight then rotate them all the same amount until the gasket is firmly seated. Going back to your original estimate, yes, somewhere between 20% and
30% is what the text book would say for Neoprene or equiv but cork is sort of an old school wildcard back from the days before torque wrenches clicked. There is probably a way to estimate the durometer of cork and then figure out the percentage associated with that but it is probably a crap shoot. That tells me that Porsche must have used it for a very good reason. If they didn't they should be shot. I wish I had thought to ask that question at Euro 928 2002.

So what does all that mean? The spec is basically tighten it enough to not squash the poor thing and enough to keep the fasteners from vibrating loose
(can't be done). Or if you are me blue locktite the bolts AND blue permatex both sides of it snug it up and forget it....That is unless you use Mobil 1.
If so it is going to leak no matter what you do :)

If you want to compute compression you can always just use the thread pitch and convert it into degrees of turn of the head of the bolt. IOW 1mm? (not sure of the actual just an example) pitch equals 1mm per 360 degrees so if you have a 3mm gasket 20% = 0.6mm of compression or .6 * 360 = 216 degrees. That won't feel like enough. Been there.

It is also expected and planned that this gasket will be snugged over its life. That means that unless you have had your 90 from day 1 and done all
your own work and not snugged that gasket then you are correct in assuming that you can measure a new one and derive inference from it. If it has been at the dealer ever there is a good chance that it was snugged some number of times and then that theory is blown. This is once more credence that Porsche must have had a damn good reason for doing this because access is a big issue for part of this gasket.

Hope this helps to frame out what is involved in answering your tightening question. Probably not what you expected.

Jay Kempf
79 US 5ish speed (next time I am in there I am getting rid of the gasket and using the crank girdle sealer and shorter bolts on the pan with proper
Torque on the bolts)

http://www.sealinfo.com/isiweb/website.nsf/EngineeringView/Relationship+of+Composition?OpenDocument

Some basic light reading.

Jay K.

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> would whoever said they had bad results with the yamabond vs. dry please provide more detail? what was the problem?

Greg, I used the Yamabond on my oil pan. (both mating surfaces and the bolts) Pan started leaking after about a year. The gasket does shrink after
time, thus leaving the bolts appearing loose. My bolts actually were loose. I could turn them with my fingers. I gently, and as evenly as possible,
snugged them all back up. About 6 months later, it was leaking again, with the same problem. I pulled each bolt one at a time and put Blue Loctite on
them and snugged them back up. Then, I took a high grade (aircraft) sealant and put it all around the pan/block/gasket vertically. Not real pretty, but
no more leaks. I'm sure I'll pay for it when I do the gasket the next time, as the sealant will be fun to get off, but it works for now. Just my
experience with it.

Chris "Bigun" Lockhart
'89 GT

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Jay, Larry,

Tonight I measured the amount of compression on my 90'S4. Took measurements in a few areas. They range from 2.5 - 2.6 mm. That's the
thickness of the compressed gasket. I also found a spot above the starter that looks like a casting defect, where the old gasket is fully exposed (never been compressed). Measures roughly 4.0mm.

So based on the 4.0mm thickness, I compute the original gasket was installed by the factory with a 35-38% compression. That's more than I
thought, but this seems to be within the compressibility range of some cork gasket materials I found on the internet.

I don't know the pitch on the bolts, but with that, one could pretty easily to figure how many turns of the bolt would yield a 35% compression.

Barry
90'S4, Slate Metallic

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I replaced the cork oil pan gasket on my 90' S4 two months ago. It's still bone dry with Mobil 1. Here's how I did it:

Instead of tightening the pan bolts using a torque wrench, I tightening them to a prescribed number of turns, yielding an even amount of desired
gasket compression. A 31% compression was selected based on the original factory gasket installation, which still had an excellent seal in the
front of the engine. This compression is also consistent with the compressibility ratings of many cork gasket materials I found on the
internet.

I purchased an Aftermarket gasket from 928 Intl. What they sold me was a cork gasket with a nitrile (synthetic rubber) binder. My install method
will work on all cork gaskets regardless of the binder and no sealant is required on the gasket seating surfaces or bolt threads.

Prior to engine cross brace removal, the engine and body were supported by only four jack stands. Overhead engine support was not used. Jack stand
height adjustment is critical. Two stands were place under the front body side jacking points, while the other two were place on the front flat
spots on each side of the clutch/bell housing. All jacking was done from the rear side jacking points. Care must be taken when lowering the engine
on the clutch housing jack stands (to raise and support the engine), such that the O2 sensor is not damage. To adjust the jack stand height under
the bell housing, I measured the floor to clutch housing distance, then adjusted the two jack stands appropriately, and I taped two 2" x 2" square
x 1/4" thick steel washers (Home Depot) on top of each jack stand. Motor mount bolts on engine block must be removed prior to raising the engine.

Degrease and clean all oil pan bolts. After degreasing the engine sides and pan gasket surfaces, clean all engine block threads with an aerosol
brake cleaner to remove any dirt or grease. Since some of the block bolt threads can become contaminated while cleaning the sides of the engine,
it's important to run a bolt in each one to ensure that they are clean.

Use acetone or other strong solvent to remove any engine oil stains from the gasket seating surfaces.

With the new gasket placed on the oil pan, and using a floor jack with a block of wood, jack the oil pan into place. Install all bolts finger
tight and so the gasket is snugly in place. Mark the orientation of all bolt head tops with grease pencil.

Working around the engine in the same direction, tighten each bolt sequentially 1/4 turn, until all bolts are 1 1/4 turn, except the last 1/4
turn should be done in 1/8 turn increments. You'll notice the tightening will get progressively tighter, and the last 1/4 turn will be very tight.
Again, that's 1 1/4 turns each bolt. This is based on a new 4mm thick gasket, and thread pitch of 0.1mm.

Hope that helps someone avoid doing it twice.

Barry
90'S4, Slate Metallic

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Can the sump be removed without having to remove the engine ??
Eric,

Yes it can be done. There is a little bar with rubber feet and a hook in the middle that supports the engine from the fender edge under the hood on the sides. Then you unbolt and remove the crossmember above the rack. The rack need not be removed, it just hangs from the tierods and steering column. Once the crossmenber is out you can do the oil pan gasket, rod bearings and engine mounts. This job can be easy or tough depending on the age of the car, how long it has been leaking and how corroded everything is under there. It really isn't that many bolts.

Some have done this job by lifting the engine as high in the tunnel it will go and somehow sneaking the pan out around the pickup tube. I haven't heard anyone describe that in say 5 years so I don't think it ever really caught on.

jfk