Is it ok to double up the copper gaskets?

[RobFrost]

I'm using 0.5mm copper gaskets under the cylinders in my 2.2 911. One needs 0.75mm and I have a 0.25mm to hand. Does anyone have experience whether it's OK to double up the copper gaskets? Or do I need to get an 0.75mm one made?

Thanks in advance.

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[mikedsilva]

It's 'OK' to do it. Not desirable of course.

I think the thicker one goes on the case... use some curil T on them..

I've done this a few times and so far, never had an issue.

I've tried having gaskets made locally, but the providers here are shocking quality. I'm safer stacking than using custom.

[356RS]

Remember, if one needs a .75mm they all get a .75mm. All cylinders have to be the same height from the engine case or your cam towers/heads will not be happy.

[Henry Schmidt]

Our experience is that even a set of "matching" cylinders are not always the same height so I would machine the cylinders with within .0005 with the intention of using a 1.0 mm base gasket.
Matching cylinders to closer than Mahle specs has been SOP for our builds ever since we got our Hardinge lathe.
Keep in mind the the case halves/cylinder decks are often inconsistent as well.

[RobFrost]

Thank-you for the advice and for the benefit of your experience. Everything has been measured very carefully.

One cylinder head is 0.25mm shorter and unless I learn a really good reason why not, it's staying that way, therefore its barrel will receive a 0.25mm thicker gasket than the others, ensuring the cams do not bind.

Does anyone know if the gaskets can be doubled up 0.5mm + 0.25mm, or must a single 0.75mm be used?

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[Henry Schmidt]

Yes, it's OK to use more than one base gasket. It's a compromise.

.25mm cylinder height difference unaddressed properly is an unnecessary compromise.
What other compromises are you planning to make?
These old engines will have issues and the "best" way to build them is to address each issue head on with the least number of compromises.

[stownsen914]

There was a recent thread where a guy mentioned a company that made him custom base gaskets pretty much any thickness for a reasonable price. Should have bookmarked it.

[draw]

One of the heads is shorter by 0.25mm and all the cylinders are the same height? I'm no expert, but if you add an extra 0.25mm shim under the cylinder, then the deck height on that cylinder will be different by that amount. Compression on that cylinder will be lower, too. Might want to look for another head or have them all machined to the same height.

Anyway, I'm the guy that had custom shims made by husseyperformance.net if you're looking for some...

Originally Posted by draw

When I measured on the opposite side of the piston, I got 0.029". This is a little too close for my comfort.

I could stack a 0.25mm and a 1mm shim together to get a better deck height, but this would be about 1.14mm and would lower my compression ratio to 9.98. So doing some googling, I found Hussey Performance who makes custom gaskets in any thickness in 0.001" increments. I gave them a call, sent them one of my shims from Ollie's, and two weeks later got a pack of 6 shims for $150...



I ordered the shims in a 0.047" thickness, which measured out to be 1.204mm...

[RobFrost]

Originally Posted by mikedsilva

It's 'OK' to do it. Not desirable of course.

I think the thicker one goes on the case... use some curil T on them..

I've done this a few times and so far, never had an issue.

I've tried having gaskets made locally, but the providers here are shocking quality. I'm safer stacking than using custom.

Thanks. Curil T both sides and in-between? I didn't realise the shims got Curil T. That's liquid gasket so technically there'll be 5 gaskets in there!

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[stubble88]

I just did this. Curil T all sides. Smoosh together. Hope for the best

[MoreGAS]

You can stack them and we have been doing it for decades with no leaks, There is a copper spray aerosol can we have put on both sides that is slightly we add for insurance, similar to using curil T, Two is no problem, 3 we try and avoid.

A larger issue is most folks don't deck their cases , especially on the aluminum 3.0-3.6 cases, this also has to be done, and a competent machinist resurfacing the heads flat and all the same. We aren't as worried about the difference in compression which is minimal with a few .001" one way or the other(calculate it and see), but that the bank clamp will not be even and things will not seal up well compression or sealing the bottom, especially if your intolerances stack up the wrong way eg- deck off .003 shallow, next cylinder deck high .002 then head cut wrong another .001", now inadequate crush on the gasket or compression surface. The last Mag case we decked it was off on the deck surface almost .015" to clean up, shocking. Then realize that with used cylinders even those on streetcars( as most racecars) w a lot of time on them, they collapse on the exhaust side if you measure around them 4 corners where headstuds are, often .002-.0025" shockingly(shows how HOT these engines run . That issue has to be recut , trued-up running parallel to the compression surface .

This is what makes buying new cylinders vs Boring and plating used ones, with those inherent additional risks(does the "Nikasil " stick) make more sense these days. Assuming one can get the bore size they want new off the shelf.

CheeRS


Kevin
GAS Motorsport

[RobFrost]

Thanks Kevin, really reassuring.

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