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Proper Sealing of Intake to Block

Discussion in 'Engine and Drivetrain/Mechanical' started by hivewax, Mar 24, 2010.

  1. hivewax

    hivewax Member

    Oil has been leaking from the back and front of the block-to-intake seals... it puddles in the pockets. The engine shop has redone this 3 times and it still leaks. They used the gray and red Permatex. The red did a little better than the gray from my observation. They want to try using cork next.

    What have you guys done to properly make a gasket seal between the block and intake? TIA
  2. apollard

    apollard Active Member

    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.
  3. hivewax

    hivewax Member

    Hmm, I watched them scruff the surface and clean it... maybe the engine vibrates too much?

    I've seen an article once in a Mustang magazine on engine building... the builder made small holes/dimples on the block contact surface to provide better grip.
  4. apollard

    apollard Active Member

    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.
  5. Horseplay

    Horseplay I Don't Care. Do you?

    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.
  6. hivewax

    hivewax Member

    Does the silicon have to cure for 24 hours??! Wow, I didn't know that... that could be the problem. It makes sense... similar to caulking. Thanks.
  7. apollard

    apollard Active Member

    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:

    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.

    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.
  8. buening

    buening Active Member

    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.
  9. jmlay

    jmlay Member

    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.

  10. gwstang

    gwstang Member

    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.

    KGMUSTANG New Member

    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.
  12. daveSanborn

    daveSanborn Active Member

    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.
  13. 66gt350

    66gt350 Active Member

    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.
  14. AzPete

    AzPete Well-Known Member Staff Member Moderator

    That dimpling is also done as an attempt to get the cork to stay in place. Never works either.
  15. Sluggo

    Sluggo Active Member Staff Member Moderator

    What Dave said. Throw those cork and rubber turds in the garbage can.
  16. Dne'

    Dne' Well-Known Member

    Wow, I'm glad I read this thread :pbj! 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?
  17. AzPete

    AzPete Well-Known Member Staff Member Moderator

    It is a rubbery type sealant that dries flexible. Yes, any parts store will have it.
  18. daveSanborn

    daveSanborn Active Member

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

  19. 66gt350

    66gt350 Active Member

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

    guruatbol Always on vacation!

    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.


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