Alan 91 C2

Has anyone looked at current design guidance for aluminum block and head engines? GM uses Multi Layer Steel (MLS).

A player here is the RA spec for the Head/Block finish, with some manufacturers calling for 10-15 RA, very shiny finish for the components.

Zirconocene

For what it's worth, Cometic offers MLS options: https://www.cometic.com/applications...rsche/928/1990

I'll be looking into this for my 944S2, in the (hopefully) not-too-distant future, so I'm very interested to see what experienced folks say, as it will be applicable to my S4. This may be a hot button topic.

Cheers

Speedtoys

Ive had cars that _require_ a MLS gasket, and the work required to support it, but do we?

Alan 91 C2

So the reason behind the question, is the disintegration of the existing gasket composition. And the role in the corrosion of the aluminum components.

Fred has written extensively about the crevice corrosion, which appears to have merit based on the action of the deteriorated gaskets.

Speedtoys

After 40yrs, you're apt to want to replace a metal gasket as well..it's time for the heads to get service/etc anyhow.

Really, we're not all up in arms over the 2015 model 928 that suddenly has corrosion under the head gasket....AND it's not even all cars.

Context.

worf928

Fred has seen… two? 928 motors’ deck surfaces? Or is it one?

Those of us that have seen many, many more than two, have a different theory that fits the data better.

FredR

Somebody who knows what they are looking at corrosion wise can as I did some 17 years ago take a look at one piece and understand in a millisec what is going on. Those who know squat about corrosion enginering can look at 1001 pieces and still be no wiser.

To date no counter theory has ever been posted by anyone to even begin an attempt to explain what happens - if you have one by all means post it- I would be more than happy to give it the once over.

FredR

Alan,

The stock gasket system in most cases is probably good for 20 years of service in the vast majority of cases- the trouble is we have no meaningful statistical data. However what i saw over here some 17 years ago were three examples in the main dealers workshop all at the same time with exactly the same problem with an average age of about 12 years. All three sets of heads were written off because by Porsche definition they were "beyond repair".

On this list I have studied something over 50 cases all with the same form. One of the problems is that folks tend to post when something goes wrong but they do not generally post when things go correctly and thus when there is no problem but we have seen a couple of such examples recently.

I raised a query about the potential performance of the Cometic MLS gasket a few years ago- responses varied from "they do not work" to "use these with no issues and no mods to the surface roughness".

Later water cooled Porsche models invariably have either closed deck construction [as in my Cayenne Turbo S] or the water passage ways have solid connections both sides of the gaskets as in the 996 and 997 models- one wonders why this may be the case!.

Alan 91 C2

all,

I appreciate the responses. Yes, the design life of the engines is much shorter than 40 years, driven by the weakest link.

The question started by looking into current practice head gaskets, and RA requirements for the aluminum block/heads.

The role of the design engineer is to make product out of materials not perfectly suited to the intended use. And bound the limit of unintended outcome. I think, for the most part Porsche can declare mission accomplished. Well except for 928 cracked dash!!!.

Speedtoys

Oh I dunno about the timeline...welding head surfaces isnt unique to the 928, its fairly common. We even see wildly neglected 928s heads that are not all that bad.
My 87 sat for a decade under a tree until 2000, had some service until I bought it in 2015, had regular service since then. When I did the head service and HG's, I had some erosion but didnt require welding. On expert advice we left it, skimmed the head, and carried on.

UP TO four decades, its time to get in the head anyhow, and gaskets are part of that job..

I love MLS gaskets, but I would hate for it to be a learning curve for us..when OE works for 3-4 decades pretty damned good for the costs involved, and it will, TBH, 30-40yrs before there is solid real world "you can put your eyes on it" evidence...

worf928

The weakest link is the string of a specific 928’s past owners and current owner where any one of them uses the wrong coolant or doesn’t change the correct coolant on schedule.

It is really that simple.

These are the facts:
Coolant eats aluminum.
Coolant has an additive package to prevent this.
The additive package becomes depleted in a multi-dimensional space of time and usage patterns.
The additive package must be compatible with *every* material with which the coolant will come in contact (hence why there is such a thing as ‘the wrong coolant’ for a 928.)

Those facts are independent of head gasket design.

Enter crevice corrosion (CC). CC will not cause two otherwise compatible substances to react. CC will not cause the proper, young coolant to corrode 928 aluminum heads. It will, however, significantly speed-up corrosion with depleted coolant.

How will an MLS gasket change that?

Fred ‘blames’ the head gasket design that enables the head deck to be wet as the cause of 928 head corrosion via crevice corrosion.

If we assume that CC will turn gold into lead and will cause fresh coolant to eat 928 heads because the head deck is wet…

…how will an MLS gasket solve that problem?

If you believe that the wet head deck is *the* problem or at least a non-trivial problem then the solution is to seal the entire binding surface of the gasket against the head deck.

How will an MLS gasket change that solution?

Ergo: For a stock, or even mildly-built, 928 engine an MLS gasket is a solution in search of a problem at best.

GregBBRD

100% correct!

No matter how many times Fred promotes his theory, it was disproved by the very first engine which anyone removed the heads from a 928 engine, without any or minor deck damage:

"A theory is automatically made invalid by the first contrary example" is a main tenet, in science or physics.

Use the proper coolant and keep it fresh has always been the solution to the 928 corrosion issue.

Unfortunately, this is exceptionally rare on low mileage examples, which sat for multiple years or on engines where the improper/old coolant was left inside, between water pump or hose failures. (Common....finding a 928 engine that got the coolant changed every 2 years with the proper type coolant might be tougher than finding the Holy Grail.)

Paper head gasket deterioration is a different matter. All original 928 head gaskets have long since exceeded their life expectancy and should be addressed.

Are MLS gaskets a solution?
In my opinion, the song and dance required to get these items to seal is only worth the effort in extreme performance engines or in engines with strange bore sizes, where a stock type gasket dimension is not proper.

worf928

This -^, AND what is the material used in MLS gaskets? How does it react with the coolant we would otherwise use?

Red Flash

For sure, an LMS gasket is not going to help the situation for 928s. In all reverence, however, Fred's remark about crevice corrosion when framed against the backdrop of another expert's (not from this forum) comments about casting variations was rather an "ah-ha" moment for me.
My understanding about Fred's comments now is that due to the head gasket design coolant is trapped and the additive packages are consumed and not refreshed in certain areas because it is trapped. The lack of circulation would then dramatically affect the on-set of crevice corrosion especially in porous areas of the casting, and once it starts, there is no way those additive packages are going to prevent the corrosion inside the crevice form going deeper. So once the condition has advanced to crevices, I tend to think the type of coolant starts to become irrelevant, and this is why certain 928s that sit really suffer from head rot, even though the coolant gets change regularly.
I happen to be dealing with a very similar problem at work right now involving slip ring manufacturing. Material science is fascinating stuff. The problem is worth enough money that we have 3 scientists working on it right now. I just want to point out that the RCA is not necessarily a "that's it" kind of an affair. Kind of like an airplane crash, there a lot of things that typically go wrong to actually lead to a crash.

GregBBRD

They make different thicknesses, but this is what I always keep in inventory:
104mm bore. .040" thick.
3 layers.
The two outer layers are thinner than the center layer. Lightly magnetic. Appear to be coated with a dark grey layer. Fire ring rolled into it, with rolled areas around the perimeter and the head bolt holes.The coating is very smooth and even.
The center layer is the thickest. Very smooth. No coating. The surface texture appears as if someone went over it with Scotch-Brite. Non-magnetic. My guess is that it is a stainless material (too heavy to be aluminum, in my opinion.) Fire ring rolled into it. No rolling around perimeter or head bolt holes.

I've personally never had one of these gaskets leak compression.(See below.)
Water leakage is a different matter, especially difficult with a welded cylinder head.
Mark Anderson once told me that he had a client who had water leakage into the combustion chambers to the extent that the client could not start the engine, due to hydraulic lock fears. (Unconfirmed, by me.)