Hey everyone, I just had a simple question on here. Does anybody know off the top of their head what the largest gap is that can be sealed by RTV? The reason why I ask is that I'm installing an intake manifold into my car and the front and end rails of the block where you normally put RTV have about an 1/8 of an inch gap with the intake manifold. (Maybe a little more) Will RTV be able to seal that or will I need to put on those gaskets for the ends of the block and manifold? Thanks in advance for any help.

 

RTV will work fine.

 

RTV silicone will seal alot wider than that (1/4") against crankcase pressure, if you use the good stuff and apply it correctly. All RTV is not created equal.
Also if you have new rubber embossed intake gaskets, they will pull down a bunch. You can expect the gap to be half once the intake is torqued down. (don't forget to follow the torque sequence).
Whatever you do don't use silicone on both sides of a rubber or cork gasket. It will make the gasket "squirt" out.
In a nutshell: use 3M, Dow, or Permatex red or black with that plastic cone on the tube (the one everyone throws away) and torque the manifold following the sequence and you'll be fine.

 

1/8" gap is normal in those areas, and rtv will work fine.

 

What would be classified as "good stuff"? A friend of mine suggested using the Permatex ultra copper RTV. Will that work fine? Thanks again for the replies... Makes me feel a whole lot better. Thought I'd have to trash my intake.

 

i like permatex black RTV.

 

I agree, Black or Grey work the best. Red is ok too. Permatex or 3m

 

Use the black or grey, i really feel like kicking guys in the jewels when they use the orange stuff. It looks so tacky...!

The only way i would use it is if it was sealing 2 parts that were painted chevy orange!

 

I haven't seen ultra copper RTV but if it's name brand and says "high temp" it's probably good. Since we're on a thread about RTV, I'd like to take the soapbox about the importance of proper application. I've seen radiator flues stopped up with RTV "worms". I've seen oil pickup screens clogged with "worms".
Think of the heartbreak of how expensive those needless repairs were.
This is a case where more is not "better" but worse. Put down a round bead and resist the temptation of spreading it out with your finger. When you do this then it doesn't look like enough and you add more. Then somebody like me ends up showing you something like mentioned above when you can't keep from overheating or don't have oil pressure.
(end rant)
The previous is for the sole purpose of future searches and not intended to make people.

 

I'll tell you right now, ultra copper sucks to use on intakes, oil pans, etc. It's a high-temp sealant, and works better when used for high-temp applications. The ultra blue isn't much better. They both have too thin of a consistency. The best rtv I've come across, and use exclusively on almost everything, is called "the right stuff". It's also made by Permatex IIRC, and comes in a metal can that's similar to a cheese whiz can. It's black in color, and has the perfect consistency. Not too thin, not too thick. It comes with a screw-on plastic nozzle that you can cut to whatever size bead you want. I used to work as a mechanic, and my boss there introduced me to "the right stuff". I haven't had a single leak from anything since I started using it.

 

"The Right Stuff" is awesome. I use it exclusively to seal intakes on the SBC. HondaBond is another great sealer youcan buy at any Honda dealer parts counter.

 

Yeah hondabond is great too. I was gonna mention that but I figured I might get flamed. Yamabond 6 is great too. And yamabond 4 is the only thing Ill use to seal metal to metal like crankcases and transmissions but havent used it on a intake yet. Yamabond 4 has fibers in it to help make a better seal.

Seth