RTV or Rubber Gaskets on Ends of Intake Manifold

[Allen N.]

I am restoring a 70 big block and am ready to install the intake manifold. It seems most people recommend not using the rubber gaskets and just using RTV on the ends.

I would prefer to keep the original look of the rubber gaskets (and not lose the judging points). Does anyone have a method of installing the rubber gaskets with a high degree of success of not having a leak?

Thanks,
Allen

[Mark E.]

Re: RTV or Rubber Gaskets on Ends of Intake Manifold

Prep the block and intake mating surfaces; ensure they are clean and dry with no oily residue. Brake cleaner works for this. Do the same with the rubber seals, ensuring they are squeaky clean and dry. This will help prevent the seals from shifting during installation.

Install them dry except for a dab of RTV on the ends. While installing the intake, use a helper, one of you on each side of the engine, to lower it straight down, taking care to avoid any front/back, side/side movement after contact.

[Allen N.]

Re: RTV or Rubber Gaskets on Ends of Intake Manifold

Thanks Mark

[Joe L.]

Re: RTV or Rubber Gaskets on Ends of Intake Manifold

I am restoring a 70 big block and am ready to install the intake manifold. It seems most people recommend not using the rubber gaskets and just using RTV on the ends.

I would prefer to keep the original look of the rubber gaskets (and not lose the judging points). Does anyone have a method of installing the rubber gaskets with a high degree of success of not having a leak?

Thanks,
Allen

Allen------


Here's the biggest problem with stock-type end seals: a variety of factors can cause the gap between the block and intake manifold ends to "shrink". These factors include, but are not limited to, cylinder head surfacing, block deck surfacing, intake manifold surfacing, side gasket thickness differences, and manufacturing tolerances. If the gap is too small, the end seals will "squeeze out" to one degree or another. This guarantees a leak to one degree or another. Using RTV instead of end gaskets eliminates this problem.

[Allen N.]

Re: RTV or Rubber Gaskets on Ends of Intake Manifold

Thank you Joe

[Mark E.]

Re: RTV or Rubber Gaskets on Ends of Intake Manifold

Allen------


Here's the biggest problem with stock-type end seals: a variety of factors can cause the gap between the block and intake manifold ends to "shrink". These factors include, but are not limited to, cylinder head surfacing, block deck surfacing, intake manifold surfacing, side gasket thickness differences, and manufacturing tolerances. If the gap is too small, the end seals will "squeeze out" to one degree or another. This guarantees a leak to one degree or another. Using RTV instead of end gaskets eliminates this problem.

Agreed- RTV is a better method than original style seals. It's a question of originality vs. functionality. Seals often work ok if deck, heads, manifold haven't been surfaced or decked.

[Mike M.]

Re: RTV or Rubber Gaskets on Ends of Intake Manifold

after thorough cleaning of all involved engine surfaces ,and the seals themselves,with lacquer thinner, i apply a thin film of contact cement to the intake, block and the pair of rubber end seals.then a small BB sized amount of RTV at all 4 corners, have a helper lower the intake onto the block. haven't had any end seals blow or squeeze out with this method. mike

[Edward J.]

Re: RTV or Rubber Gaskets on Ends of Intake Manifold

after thorough cleaning of all involved engine surfaces ,and the seals themselves,with lacquer thinner, i apply a thin film of contact cement to the intake, block and the pair of rubber end seals.then a small BB sized amount of RTV at all 4 corners, have a helper lower the intake onto the block. haven't had any end seals blow or squeeze out with this method. mike

I agree with Mike the rubber seals need something to hole them in place, I have had luck with 3m weatherstrip adhesive. But contact will work.

[Joe R.]

Re: RTV or Rubber Gaskets on Ends of Intake Manifold

I had an annoying leak in the rear intake gasket of my 327 that took me a while to pin down. When I pulled the intake to fix it, I decided to use Permatex Ulta Copper RTV for the rear seal, but use a correct-style rubber gasket in the front to keep the original appearance. One nice thing about the Ultra Copper is that its color blends in well with Chevy Orange.

Even though my car was judged several times at NCRS events, no one ever noticed that I had used RTV in the back, so I never got a deduction for it. On a 327, the area where the rear seal is located in very hard to see. I'm not sure what the situation is for your big block.

Interestingly, after a few years, the front seal started to squeeze out and leak. The RTV rear seal stayed bone dry.