Proper Sealing of Intake to Block

I think you'll find most everybody does the silicone gasket route, just like they did. Mine is 11 years old, and no leaks. I'd think there is some other issue, like not cleaning the surfaces well, paint on surfaces, a small pososity in the metal, etc.

 

Holes might help, especially if you have a lot of crankcase pressure. I also make sure to let it cure at least 24 hours - it's a thick bit of silicone in there.

 

I would also recommend that after a few heat cycles you go back and re-torque on all the intake bolts. I've never had to do more than make sure the mating surfaces were square and clean to get my intake installs to remain leak free for years.
Cork will give you nothing but problems.

 

24 hours - if thin, you can get by with less, but the intake area is a pretty thick bead. Heck, it needs 7 days to reach full strength:

TYPICAL CURING PERFORMANCE
Permatex Black Silicone Adhesive Sealant cures on
exposure to moisture in the air. The product dries tack free in
1 hour and fully cures in 24 hours. Cure times will vary with
temperature, humidity and gap.

PERFORMANCE OF CURED MATERIAL
After 7 days at 25°C (77°F), 50% Relative Humidity
Typical Values
Hardness (Shore A) >18
Elongation, %* >350
Tensile Strength, N/mm2 (psi)** >1.2 (>170`)
*Material will stretch 3.5 times its original length before breaking.
**Amount of force required to break material.
http://www.permatex.com/documents/tds/Automotive/81158.pdf

 

The two key items are getting the silicone thick enough and letting it cure long enough. The crankcase pressure will blow a hole through the silicone if it hasn't cured long enough.

 

Remove the intake/ Clean everything good. Clean it again. Then use brake leaner or acetone to remove the oil. Use "The Right Stuff" gasket maker on the end seals.

Mike

 

Lacquer thinner works very well also. The towel you use, to wipe the surfaces down with, must be spotless when you are finished. No oil or dirt still showing up or you will have leaks.

 

I had the same problem with my Edelbrock performer 289 on a 302. I used the most oil resistant silicone and it leaked in the back. I redid it twice before checking further. Turned out to be the PCV valve was stuck mostly shut causing a pressure build up.

 

Just so that it's clear.....

There was mention of using cork/rubber front and rear gaskets in this thread. IMO, the best results are obtained without using any gasket, but only a thick bead of RTV.

 

When I took off the intake from the wife's mustang the other weekend. It was sealed with just a bead of silicon, nothing unusual. But what I did notice, is that it looks like someone in the past had taken a center punch and dimpled the sealing surface on the block front and rear. I'm assuming that this is supposed to help the silicon stick to the block.

 

Wow, I'm glad I read this thread bj! I'll be putting my intake on very soon. It's just sad to have to wait so long to crank the motor. What is "RTV"? O'reilly has it?

 

Sorry, RTV is just another name for a product I'm sure you're already familar with.....

 

RTV - is a type of sealant. RTV is an acronym that stands for Room Temperature Vulcanizing -- ie. it cures at room temperature.

 

OK, I have built six different small blocks. I always use the rubber gaskets and use some RTV in the corners. I know Dave is good, but I disagree with the use of only RTV. Sometimes I use a small bit of RTV on the block and on the intake, just barely any at all. Then when you torque the intake on make sure the gaskets do not squeeze out.

I have never had a leak in any of the engines I have build. Even the one I learned on in college engine machining class.

Sorry, Dave.

Mel