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Old 05-30-2013, 09:57 PM
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Manifold to Exhaust Bolt Size

Question for the part number gurus...

I've posted this a couple other places...the more lines in the water the better your chance of a catch...BUT...

I'm looking for the size/tpi of the bolt that connects the exhaust pipe to the exhaust manifold on 70's SBF's. I've got a 302 with 78 and 75 exhaust manifolds replacing my old 69 manifolds that were cracked and broken, but the old bolt doesn't match up. Long story short, I need the bolt that connects the manifold to the exhaust pipe. I can't find one in my limited supply that fits.

Thanks!
Jim
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Old 05-31-2013, 12:31 PM
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They're not bolts, they used studs here. They're 7/16" NC if I'm not mistaken. Dorman used to make these, proably still do.
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Old 05-31-2013, 02:08 PM
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BD,
Thanks for the reply. On my old manifolds, the RIGHT had studs, the LEFT had bolts. On the new (salvage) manifolds they're just threaded holes on both sides. I picked up 7/16-14 bolts as that's what went in the old LEFT manifold and I figured the newer ones would take the same. The 7/16-14 bolts go in about two threads and stop. I tried a 3/8 bolt it just slides right in and out. So 7/16 is the right diameter. I think NC would = 14tpi, meaning I might just need to tap out my manifolds. But if they're 16 or 12tpi I could really make a mess of things!

Thanks again for the reply!

Jim
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Old 06-01-2013, 06:34 PM
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As Baddad has said, the manifolds should be fitted with studs, not bolts. The thread is 7/16-14, i.e. standard coarse thread.

The fact that you found bolts used simply indicates that someone improperly reassembled the parts at some point.

The threads on the manifold are regular threads, but the studs have a special interference thread design to keep them from unscrewing. Double nut them to insert (poor quality replacement parts may not have this feature).

You can probably still get the studs from your local Ford dealer.

Use never-seize on the nuts.
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Old 06-01-2013, 11:41 PM
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I think my 390 has a somewhat similar setup. When changing a flang gasket I found a crack in the manifold. I salvaged a good replacement manifold. As far as the studs, i replaced with all new grade 8 studs and hardware. The parts store had quite a selection but all were either shorter or longer than what I needed. I got the longer studs and ground them down to the length I needed. I then applied a bit of High temp locktite and snugged them up.

This seemed to be the best way to replicate what Ford did on a dime. Hope this might help.
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Old 06-03-2013, 08:14 AM
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Beans,
Thanks for the details. I got her sorted out over the weekend. I was worried I might crack the iron (or more likely cross threads) but I discovered that after running them in, the threads on the stud went from sharp points to dull rounds. I'm guessing this is the interference design you mention as the stud threads themselves were identical to the bolt threads.

Oh, and I'm a big fan of anti-seize!

Thanks Crazy for the info. For your sake, and the sake of anyone who comes after you, I hope you those studs never break or need to come out!

At any rate, this hurdle's been crossed. Thanks fellas.

Peace,
Jim
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Old 06-03-2013, 08:14 AM
 
 
 
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