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Old 05-13-2013, 01:17 PM   #1
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Intake manifold question. Any ideas?

1990 YJ 4.2 Inline 6


I've had vacuum leak issues ever since I bought the new Offenhauser Intake manifold and only vacuum leaks on the manifold itself on the head. Me and a good shop I deal with have concluded that the manifold isn't built right.

The cylinder head is not messed up. I know for sure.

We have tried different kinds of gaskets and none of them will seal up right. We got it to run really good but not even a whole day and while driving it around it just starts to leak again. And every time we take the manifold off the gaskets aren't messed up but it's not sealed up.

They suggested taking the manifold to a machine shop.

I've thought about just getting the factory manifold but my old one is trash and of course I can't find any new ones.

Any ideas? What should I do????

BTW if anyone has a factory manifold who is interested in a trade well also let me know. BUT IT NEEDS TO BE DECENT AND NOT BRITLE LOOKING!!

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Old 05-13-2013, 02:09 PM   #2
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Is it leaking where the intake manifold and head mate? Or could it be carburator to intake. If it is at the head try some copper gasket compound. Torque to spec. Let it sit over night and retorque. It might be worth a try.

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Old 05-14-2013, 06:40 AM   #3
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Quote:
Originally Posted by CMike357 View Post
Is it leaking where the intake manifold and head mate? Or could it be carburator to intake. If it is at the head try some copper gasket compound. Torque to spec. Let it sit over night and retorque. It might be worth a try.

Yeah it's where they mate. over and over again with different kinds of gaskets it leaks. Now we haven't done any liquid gasket but that's what I was thinking on trying but wasn't sure if it would work. We are worried about the new manifold now being perfectly flat where it mates to the head. But visually it looks fine.
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Old 05-14-2013, 07:21 AM   #4
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I would take it to a machine shop and have them mill the gasket surface. At least that way you know it's flat. GL.
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Old 05-14-2013, 08:56 AM   #5
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is the manifold really new or just new to you? if new I'd contact offenhauser. if used lay a straight edge across the flanges and see if its warped. also, the manifold mounting changed in the early eighties, you might have the wrong manifold. I run a offenhauser manifold I got off ebay and it works great, really worth the effort to get it working. the holley 390 cfm is a great choice for a carb.

EDIT. the manifold must be tightened in a pattern starting in the middle and working out. you can find the pattern in most manuals.
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Old 05-14-2013, 10:41 AM   #6
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yep brand new. that's what summit racing said. I figured it was worth fixing but wondered what a good option was. I will lay a straight edge across it but how hard to you think it would be to just do some small amount of grinding with a air grinder?
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Old 05-14-2013, 11:46 AM   #7
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I wouldn't use an air grinder. If it needs to be repaired it should be machined, for a perfect surface.
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Old 05-14-2013, 12:13 PM   #8
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if it needs repaired, the seller needs to replace it (its it was sold as new!)
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Old 05-14-2013, 08:02 PM   #9
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Even with my factory intake and exhaust, I've found that the bolts loosen up and need to be retorqued at least once (sometimes more than once) before it holds tight.

Just retorqing the bolts that loosed didn't cut it for me and left me constantly chasing a loose bolt. I've found that when retorquing the intake/exhuast manifold bolts that you need to slightly loosen all of them, then retorque all of them sequence. At least that's what worked for me.

Ditto on double checking the manifold mating surface, and while you're at it check the head to make sure the manifold mounting surface is true.

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