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broke all bolt tabs on the upper side of an EFI lower intake

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arse_sidewards
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Posts: 846
Joined: Mon Jan 21, 2013 7:18 am

broke all bolt tabs on the upper side of an EFI lower intake

Post #1 by arse_sidewards » Sun Jan 03, 2016 8:08 pm

I'm in the middle of replacing a core support. I'm tacking half a dozen other little things including an exhaust leak while I'm at it. I pulled the upper intake and found that every one of the tabs on the top of the manifold was broken off. None of the lowers were broken. The exhaust manifolds were fine. I know for a fact that I looked up the torque spec and torqued them down in the proper sequence in three steps. I'd have noticed if I broke a tab when torquing it down. There was no OEM exhaust gasket. I installed one. It leaked, now I'm replacing it with sealant. I'm also replacing the bolts with studs. The truck didn't run poorly (probably because speed-density EFI is pretty resistant to vacuum leaks).

What did I do wrong that caused this?

Could the exhaust gasket have raised up the exhaust manifolds enough that the bolts weren't doing much to support the intake and as a result it leaned toward the driver's side breaking the tabs?

I have a spare intake but I'd rather not break this one too.
1994 F150 4x4 8ft, engine is basically stock.

66" leafs, extended radius arms, lockers in both ends, nothing special.

Sick6Turbo
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Posts: 78
Joined: Sat Dec 19, 2015 12:53 pm
Location: Almond, Wi.

Re: broke all bolt tabs on the upper side of an EFI lower in

Post #2 by Sick6Turbo » Sun Jan 03, 2016 9:02 pm

I'm betting on the thickness change with the added exhaust gasket.

I had the same issue when I surfaced efi mani's, took quite a bit off to make them straight. On the last sequence I thought I heard something not right, 2 or 3 broken tabs on the lower intake.

Picked up another lower and matched up mani's and gaskets til the combination yielded the same thickness on intake and exhaust tabs so the washers sit flat, and all was good.
Dale
79 F-100 turbocharged 300 rear mount 20 psi
Stock EFI bottom end, mild port carb head
12.44@106 1/4 mile in 2015

arse_sidewards
Registered User
Posts: 846
Joined: Mon Jan 21, 2013 7:18 am

Re: broke all bolt tabs on the upper side of an EFI lower in

Post #3 by arse_sidewards » Wed Jan 06, 2016 4:43 pm

I'm going to reinstall the manifolds tomorrow and will try my best to surface them accurately. Are there any tricks I could employ that would allow more wiggle room for differing thicknesses? I'll be using sealant on the exhaust manifolds and a gasket on the intake.

Is it worth swapping to studs at present? I've got a set of studs I made but am unsure if it's worth the hassle. What about just using studs in a few select positions to make it easier to align three manifolds (two of which will have sealant on them) and a gasket?
1994 F150 4x4 8ft, engine is basically stock.

66" leafs, extended radius arms, lockers in both ends, nothing special.

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