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Thread: Big block manafold problem!

  1. #1
    Senior Member MASTER BUILDER
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    Oct 2003
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    Big block manafold problem!

    I have a big block I have been trying to fix a problem with the manifold.
    the engine is a 502 bbc with world products heads.
    the manafold is from the original 427 that was in the car.
    the problem is the intake gasket always leaks in the cam valley. I have replaced it several time and it still leaks after a long drive.
    I found out thru checking, the manafold when installed is not sitting deep enough into the block to seal the ports. When looking at the old gaskets. the sealing surface is about 1/16 or a bit wider on the bottom of the manafold ports.
    I tried a aftermarket manafold and it seems to match the ports better.
    The customer is particular and with the aftermarket manafold, I have to use a really low profile air cleaner to clear. ( it is a 66 vette )
    He is wondering why an aftermarket manafold will work and not the one on from the old 427. I am wondering the same.
    anybody run into this? I told him the heads may have been cut, but that still does not figure whay the aftermarket one works.
    the gasket is a square bore 1/16 thick.
    thanks
    Al

  2. #2
    Junior Member APPRENTICE
    Join Date
    Jan 2003
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    17
    The intake may need to be machined slightly to fit correctly, but before doing that I would switch from the 1/16 in gaskets to 1/8 in gaskets if this helps, but if that is going the wrong direction then you will need to have the intake machined. Also don't use the end gaskets if you are attempting to, instead use a thick bead of silicone sealer.

    Good Luck.

  3. #3
    Senior Member RACING JUNKIE
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    I always had the best luck with using silicone on the end rails,also.I found that Permatex's Ultra Black holds up the best.47,ooo miles and counting.The blue stuff doesn't do well with constant oil,regardless of what the tube says
    "The problem with quotes on the Internet is that you cannot confirm their validity"- Abraham Lincoln

  4. #4
    Senior Member RACING JUNKIE
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    Somebody angle milled the heads, but didn't do the manifold to match!

    Or, someone angle milled the manifold to fit another set of heads, which no longer fits correctly on these heads!

  5. #5
    Senior Member RACING JUNKIE
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    Quote Originally Posted by OneBadGMC
    Somebody angle milled the heads, but didn't do the manifold to match!

    Or, someone angle milled the manifold to fit another set of heads, which no longer fits correctly on these heads!
    I'm with you on this too, get a protractor and measure the angle of the intake and compare it to the heads, you'll see the difference. However using a thicker gasket just might take of the problem without doing anything else.
    I also use the ultra black on the end rails. I lay down a medium size bead and let it "SKIN" up about 30 minutes and then install mainfold, after it dries ( 24 hours) I come back with a razor and trim the excess for that clean and neat look.

    >< Cp
    ***IN GOD WE TRUST***

  6. #6
    Senior Member RACING JUNKIE
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    Talking about angle mills,did you build this motor/buy these heads?If you did that wouls rule that out.Every aluminum manifold I have bought I had to have milled.But I'm kinda picky,too.Never had one perfect right out the box.Make sure you use right sequence when tightening those bolts.More important than you might think
    "The problem with quotes on the Internet is that you cannot confirm their validity"- Abraham Lincoln

  7. #7
    Senior Member MASTER BUILDER
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    I did not build the engine.
    I agree, the manafold has to be milled.
    The customer does not want to mill this (original) manafold.
    I have an aftermarket one I am going to mill for this application.
    thanks guys
    Al

  8. #8
    Senior Member RACING JUNKIE jmarksdragster's Avatar
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    If the bottom is open more, it's likely the manifold was milled in the past and the heads are stock. Heads are cut on the exhaust side, and would open the top with an uncut manifold. Try a Performer or Torquer II.
    Mark Whitener
    http://racingfuelsystems.myfunforum.org
    __________

    Good work isn't cheap, and cheap work can't be good.


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