Making thin film RTV gaskets

[raygreenwood]

I think I posted this at one time but I cannot find it...so since it came up in a couple of posts this week I decided to do a better one.

I originally started using this to seal 004 transmission cases.....and it worked pretty good....and now use it with Permatex gear oil specific RTV which works MUCH better
https://www.amazon.com/dp/B0023GM2KK/ref=asc_df_B0...6710904314

I have used this method for numerous engine case joints...and it seals perfectly. Very uniform.

It is also perfect for refurbishing the phenolic block intake manifold gasket sets on type 3 and 4....after you carefully sand off the original gasket on a sheet of glass with 800-1200 grit paper and degrease them.
I use Permatex gray or black on those.

But here is the basic method:

So for this how to...I just used a semi-clean case I had on the bench and wiped the cases edges with MEK. This is just a sample for the camera and not a real build

A sheet of cheap plate glass with the edges taped (or you can Dremel them smooth). The "X" is marked on the backside wit ha Sharpie marker so I can show how thin this is for the camera...and I use it this way as a visual gauge for me as to how even the RTV is in thickness.

Run out a couple of thick strips of RTV on the glass.

Start rolling it out. At first the roller will just ski across it until it thins out. Then use even and overlapping strokes.


The roller is called a "brayer" it is for rolling out block printing ink. This is a cheap one with a plastic body. They make them in widths down to about 3/8". They are available in the $8-20 range at most hobby and craft shops like Hobby Lobby.
I have a 1/2" wide one for working around studs and couple of wider ones. The harder the rubber the thinner it will roll out any liquid or paste.

These work by""shearing" the paste using its natural viscosity and tack.

WARNING: DO NOT do too much at one time. This method makes the RTV cure about 10X faster. So your working time is about 8-15 minutes. After that the RTV will be nearly dry to the touch (still needs to cure for hours though). After that I immediately clean the roller with MEK or acetone and I razor blade the glass clean for a new batch.

In about 15-25 strokes...and its speed and pressure dependent....it thins out to a VERY even layer and is transparent or translucent its so thin. You can see the "X" on the back side of the glass through the RTV.

This took less than 1 minute

Just for this demo....I am using one of my precision wet thickness measuring tools to see how thick this RTV is.

This tool has an NIST certificatiin to accuracy of 1 micron (1/25,400th of 1 inch). For reference.... .001" = 25.4 microns.

You can see that this RTV layer is right at 1.9 microns thick.

So roll across the flat sealing surfaces just like you rolled on the glass. Make a pass on an area and then reload the roller on the glass...work quickly. Make two quick transfer passes to all areas and look for uniform color.

I put X's with sharpie marker in strategic areas so I can see that it is rolling on thin and evenly.

You can see from these close ups...how smooth and of uniform texture this method is.

You need to let this dry completely...and typically for a case parting line...I run a second layer. I do this to both sides of the case. The total build is usually about 4-6 microns per side for a total of 8-12 microns...so about 1/2 of .001".

These go together dry and the there is just enough interlacing surface texture and crush to give perfect sealing. In some cases I have built them out to a total of right at .001". I do that for the phenolic blocks because the machine kerfs in both manifold and head are deeper. Ray

[Lars S]

Nice input Ray, did not know of this method before!

How hard is it to split and clean a case after it has been seald with this method?


/Lars S
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[raygreenwood]

[scrivyscriv]

Thanks for sharing that. Another tool for the toolbox.
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Robert in Memphis
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If you're ever in the Memphis area, you are welcome to stop by for advice and help.