Silicone gasket sealer

[Dan P.]

I went to GM school when this stuff first came out .When used correctly it works great . Incorrectly and it can cause a lot of problems . We were taught that it has to be .011 of A inch thick to work.The proper way is to lightly tighten the part till the sealer is squeased out all around the part and then wait 1 hour before tightening . I like overnight. If you tighten the part with out waiting the sealer is force out and very little is left to seal the part .I do not know how many times I have torn something apart to find the silcone has has come loose and plug something up .I had A old Harley Panhead that had no oil presure when it was warmed up . Found A long piece of silicone between the check ball and seat. They do make the new stuff that says you can tighten right away . I still wait A hour to give the stuff an little time to cure .

[Dick W.]

Re: Silicone gasket sealer

Dan, another problem with the silicone is that it has acetic acid in it. We used to rebuild spare transmissions using silicone on the gaskets. Sometimes the transmissions would sit on the shelf for 8-9 months. We started having problems with bearing failures, especially the input shaft bearing failures. Eaton/Roadranger service rep's had seen the same problems in other fleets. It was finally determined that the acetic acid was etching the bearings, setting them up for failure.

Another product that I have always liked when mating two machined surfaces is Loctite gasket maker. Use their surface prep spray to clean the surfaces and then apply the product. Let it sit for 24 hours to allow it to properly set up.

[Ray G.]

Re: Silicone gasket sealer

Hello Dan and Dick;

Do you know if the bearing problem occurred on gaskets coated with silicone and/or when silicone gasket sealer was used in place of a gasket?

If the trans was put into service immediately, do you think the fluid would neutralized the the acid?

Thanks for your help.
Ray

[Dan P.]

Re: Silicone gasket sealer

Dick could answer the question beter than i could.Silicone should never be used between two machined surfaces .The best application is if one part is a cover . Valve cover rear axle cover or if there is air gap between the parts like ends of the intake manifold.When using silicone with a gasket you have to seal 4 sides instead of two .Both side of the gasket and both parts.Silicone is beat used with out A gasket . Now if you have a major flaw in the part say A broken ear silicoen is great .
I tighten the part lightly till the silicone is squeased out and let the part set overnight. Now you have formed the gasket to the part and now compresing it insted of squeesing it all out.

[Dick W.]

Re: Silicone gasket sealer

Hello Dan and Dick;

Do you know if the bearing problem occurred on gaskets coated with silicone and/or when silicone gasket sealer was used in place of a gasket?

If the trans was put into service immediately, do you think the fluid would neutralized the the acid?

Thanks for your help.
Ray

We did not notice the problem when the part was put into service shortly after assembly, only when it was stored for a lengthy period of time

[Jim T.]

Re: Silicone gasket sealer

When I bought my 85 in 1992 I had to repair leaking valve cover gaskets. Service history documents showed previous repair at the Chev dealer.

Black silicone was used by Chev dealer on both valve covers. Found this black silicone wrapped around the upper part a few of the pushrods.

62K miles later, no engine problems yet.

I used real valve cover gaskets installing the valve covers.