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Intake gasket leaks/ oil consumption problem

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  • Intake gasket leaks/ oil consumption problem

    Has anyone else encountered this with their pro-flo 4 intake on a small chevy? Engine is a GM ZZ4 short block with AFR 190 vortec style heads and the Pro-Flo 4 for vortec style heads. I have had the system installed for 7 months now and it runs great, but I am sucking up tp 2-3 quarts of oil every 3000 miles thru the intake gaskets. Never encountered this before on a SBC . I have pulled the intake off 3 times now and tried 3 different types of gaskets and sealant techniques with no luck. It appears that to get a proper seal I need to have both sides of the intake milled to change the angle s for better seal and gasket pre-load at the bottom of the gaskets in the lifter valley. 0.015" on one side and 0.006 on the other. Is this a common thing? or am I just the lucky one?

    Any suggestions would be helpful before I have to have this machine work done.

  • #2
    Sorry to hear that you've been having this issue. What's likely going on is that the material around the injector bosses may be interfering with what we call the "break back rail" on the cylinder head. See the pic below for an example of what a break back rail is. When this happens, the intake manifold can't be cinched down to compress the intake gaskets which can result in a leak to the lifter valley.

    break_back_rail.jpg

    The problem stems from the intake manifold originally being designed for an Edelbrock cylinder head that didn't have a break back rail thus there isn't a clearance problem. But stock iron heads and some aftermarket aluminum heads use a break back style rail which can interfere with the manifold. If you try dry fitting the manifold without gaskets and checking this area for clearance, you'll probably see the problem. Usually a couple of passes on a belt sander gets you enough room but if you'd like them to be more precisely machined, you can do that too.

    Can we at least send you a set of gaskets for your troubles?

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    • #3
      Are your AFR heads part number 912?

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      • #4
        Originally posted by Nate S View Post
        Are your AFR heads part number 912?
        Yes, they are also drilled and tapped for the old style bolt pattern as well.

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        • #5
          Looking at pics of AFR 912 heads online, it looks like they have a break back valve cover gasket rail. Is that correct?

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          • #6
            Originally posted by Nate S View Post
            Sorry to hear that you've been having this issue. What's likely going on is that the material around the injector bosses may be interfering with what we call the "break back rail" on the cylinder head. See the pic below for an example of what a break back rail is. When this happens, the intake manifold can't be cinched down to compress the intake gaskets which can result in a leak to the lifter valley.

            break_back_rail.jpg

            The problem stems from the intake manifold originally being designed for an Edelbrock cylinder head that didn't have a break back rail thus there isn't a clearance problem. But stock iron heads and some aftermarket aluminum heads use a break back style rail which can interfere with the manifold. If you try dry fitting the manifold without gaskets and checking this area for clearance, you'll probably see the problem. Usually a couple of passes on a belt sander gets you enough room but if you'd like them to be more precisely machined, you can do that too.

            Can we at least send you a set of gaskets for your troubles?
            There is plenty of clearance between the manifold and the rail. The gasket on there now is the Edelbrock 7235. They were installed only 2 days ago so I wont know if they are leaking yet until I get a couple of hundred miles on them.

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            • #7
              Hmm well I can't readily explain your issue then if you're not having a fitment issue at the rail. My knowledge is more directly EFI related so I suggest calling into our tech line to speak with a tech rep about manifold fitment issues: 1-800-416-8268. In speaking to them, they've experienced fitment issues due mostly to break back rail interference. Don't know that we've heard much about oil consumption without there being some obvious interference with the rail. Are there obvious signs of oil seepage on the gaskets? Signs of oil contamination on the spark plugs? Blue exhaust smoke?

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              • #8
                Yes, oil seepage on the bottom of the gaskets, fouled plugs and oil in the intake runners when I pull the manifold off. No noticeable smoke. The 0.120" thick gaskets are getting compressed to 0.111 at the top of the ports and 0.119 at the bottom on the passengers side and 0.111 top of ports and 0.112 on the drivers side. I will call the tech rep about the fitment issue, but I am thinking that milling the intake surfaces to the correct angles is the only solution. Thanks for your attention.

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                • #9
                  If you intake is sucking oil. You have 1 of 2 problems. Either the intake is bottoming out on the front and rear china walls or the intake is cut on the wrong angle..AFR are pretty dam good heads. I have seen heads drilled wrong which made too much clearance between the intake surfaces. The fix for that is offset dowel pins. Does the intake fit flat against both heads with no gaskets? Did you run the engine before with a carb intake and no issues?

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                  • #10
                    Originally posted by Scselt View Post
                    If you intake is sucking oil. You have 1 of 2 problems. Either the intake is bottoming out on the front and rear china walls or the intake is cut on the wrong angle..AFR are pretty dam good heads. I have seen heads drilled wrong which made too much clearance between the intake surfaces. The fix for that is offset dowel pins. Does the intake fit flat against both heads with no gaskets? Did you run the engine before with a carb intake and no issues?
                    I only ran the engine with the AFR heads for about a week before installing the Pro-Flo. Never tried the intake without gaskets, but with 0.120" thick gaskets torqued I have plenty of space between the intake and china walls, 0.150" front and back if I recall. I think I have some bad geometry happening.

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                    • #11
                      ZZ4 block deck surfaces could be milled wrong also.

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