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Slumlord
 
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Join Date: May 2001
Location: Canada
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Gasket Experts

This is sort of Porsche related (because I have similar problems with my valve and timing covers on my 2.7) but all these sealant 'reviews' and ideas are starting to drive me crazy.

I've got silicone, Hylomar, Yamabond, Curil-T and case sealer in my toolbox now, oh and also high temperature grease and anti-seize compound. I seem to pick up a new compound every week. In my pre-Porsche days I had one material (paper gasket) and one sealant (Permatex gasket goo).

So, my problem of the moment is and older car (pre-1930) with a wavy timing chain cover (ie not as flat as I'd like on the mating surface) bolting up to a pretty flat aluminum case. How should I seal this? I'm thinking the thicker cork-type material with Hylomar on both sides would be best, or maybe paper with Curil-T, or just use silicone? Too many choices for me!
Old 03-01-2006, 10:37 AM
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I'd try to make the cover flat again by wet sanding on a peice of glass. If that won't work then get a new cover (good used cover).

-Andy
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Old 03-01-2006, 11:59 AM
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Slumlord
 
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Unfortunately neither of those is an option. The engine is quite rare, the piece is too only a stamping, so I doubt I could lap it flat and it is too complex to make a new one.

I could make a series of steel re-inforcement plates on the bolt-up surface that would help pull if flat. But I still need to choose a sealing method.
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Old 03-01-2006, 12:15 PM
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Hylomar will get washed away by the oil. I doubt that anti-seize and high-temp with do you any good here, either. You essentially want to fill a gap. How about cutting a gasket out of 2mm thick kork sheet material. It would be period-correct and probably being able to fill gaps much better than any compound.`

To really get it sealed you'd need to figure a way to unwarp the cover.

Good luck,
Ingo
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Old 03-02-2006, 10:56 PM
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Slumlord
 
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Is that true about Hylomar? I thought that it was good for oil/gas etc...What is it meant for if not a general gasket sealant?
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Old 03-03-2006, 06:11 AM
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It is. But is more or less acts like a dressing (high-viscosity lubricant) rahter than a true sealant with gap filling capabilites. In other words it wets the rubber of O-rings and such to allow their subtle movement in the gasket seats.

I recently had a chain tensioner cover on a 964 that was ever so slighly bent of shape at one end and no Hylomar in the world did help to seal that leak. The oil under 5 bar blew right through the 0.1mm gap on one side. It literally washed the Hylomer away. Once I sanded the cover flat the issue was resolved.

Ingo
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How about a NoBadDays DualChip for 964 or '95 993
Old 03-03-2006, 08:13 AM
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Slumlord
 
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I guess I'm okay everywhere else with my engine. I used Hylomar on every paper gasket on this engine, and there are a lot, but they all seem to mate up nicely.

I'm wondering now if Curil-T would be any better an a good fit-up?

I have to fix the chain cover somehow. I guess there is no reliable short-cut.
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Old 03-03-2006, 09:06 AM
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I made up a few hard to find gaskets for a irreplaceable piece with gasket material used in the aircraft industry. Check with an aircraft supply house - I was looking for the red silicon gasket material, but was steered to something with better resistence to oil. Let them know what you're doing and I'm sure they would have some kind of recommendation.

Regards,
Andrew M
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Old 03-03-2006, 10:26 AM
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Sounds just like a Toyota 4runner. They do not use a gasket. They use a special RTV sealant with mixed sucess.
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Old 03-03-2006, 02:40 PM
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Gaskets!

Well, I've been in the gasket industry for about 17 years.

Typically when there is a leaking joint, people nearly always blame the gasket when it's really the flanges or installation

Your problem is a very common one that can be difficult to solve, but as with everything you can try to make the best of a less than ideal situation.

Firstly, Hlyomar was developed for very rigid flanges and gaps of less than .010" (if I remember correctly), so I assume your cover is bent beyond that.

I understand that you are dealing with an old warped stamping, you need to do your best to flatten it. I learned and old trick once on stamped oil pans.

Support the oil pan with a socket on the side of the pan that hte bolt head touches and use a ball peen hammer to remove the distortion. If you over do it, actually thats not a bad thing.

Point is that you do not want the bolt hole to be deformed downward.

I also assume that the same thing has happened to you cover as the oil pans, and that is that at one point it was over tightened and distorted the cover at the bolt holes.

This is the ABSOLUTE worst place to have distortion, if we consider that any flange will distorte, general beam bending priciples tell us that the distortion will be greatest directly between any two bolt holes. Make a mental picture of a bowed flange in your head (or better yet on paper) now raise up one of the sides where the distorted bolt is and the center gap gets even larger. (sorry to be so basic).

A picture is worth a thousand words applies here, but I don't have a picture, what I would show you is a Fuji film anaysis of a gasketed joint. Fuji film is an engineering grade carbon paper that turns shades of red at different pressures. If you were to bolt up your cover with a gasket and fuji film, you will see the resulting load that the gasket lives with. Now different materials need different loads to seal, I won't go into that.

These tests are invaluable for looking at how a distorted cover or machining flaw affect sealability.

As far as how flat is flat goes, typical "soft gasket" materials will compress about 10 to 30% at 5000 psi (which is a lot higher load than your timing cover will see). I would assume 5 to 10% in yoru application, so if you are using a gasket .062" thick the MOST gasket compression you will see would be .006"

For the most comprehensive data on gasket materials, see www.sealinfo.com

Now, cork rubber material will have much higher compressability, and also present new challenges.

For your application, depending on flatness, you may need to use a cork rubber material.

I would suggest using a gasket adhesive on both sides of the cork/rubber and DO NOT OVER TORQUE as you will just deform the cover again!

You should use locktight on the bolts. My best anaolgy for this is that you are trading off torque retention for compressability, consider that if you were to use a steel gasket, it would not compress very much, but you would have very little relaxation of the gasket material (because its steel), then consider you would use foam rubber, it would conform very nicely to the flange, but over time will loose the clamp load on the joint.
This is refered to as stress relaxation or creep relaxation.

Since the elimination of asbestos in gaskets many new materials were developed to replace the handfull of materials with asbestos.

In the last 5 years there have been great improvements in the sealability of "soft gasket" materials. The leakage rates of these materials are an order of magnitude better than the materials they replaced. Having said that , cork/rubber is still in large part the same as it has been.

Hope this helps, let me know if you have any other questions.


Jeff
Old 03-05-2006, 09:00 AM
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