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Replace Exhaust Manifold Studs?

Bronco648

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The studs on my exhaust manifolds have seen better days (I'm talking about the studs that hold the Y pipe to the manifolds, not the bolts that hold the manifolds to the heads). There's a nut right where the stud meets the casting. At this point, is there any chance that they will simply unbolt? The manifolds are from Oklahoma and are not that rusty.

Or, am I better off running a die over the threads to clean them up and get new nuts?

Lastly, is there any chance you could cut new threads by going one size smaller (say M8 to M7) if the thread pitch was the same?

TIA
 


Uncle Gump

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Heat them up good... quench the stud with some PB... they will most likely come out.
 

Bronco648

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Heat them up good... quench the stud with some PB... they will most likely come out.
I do not have an oxy/acetylene set-up. Would MAP gas work or isn't that hot enough?
 

Uncle Gump

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I think that would work...
 

Bronco648

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This is what they looked like when new, good luck.
I didn't realize they were two different sizes. :unsure: Maybe running a die over them would be a better idea. @AndyB. Do you know the thread size and pitch by any chance?
 

AndyB.

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M10x1.5 was the closest match I had, but it wouldn’t chase these cleanly.
 

Bronco648

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M10x1.5 was the closest match I had, but it wouldn’t chase these cleanly.
Hmm, OK. With a pitch gauge I was able to determine that the pitch was 1.5 and M10 is the only thing that fits, diameter-wise. Why would these studs be something special/weird (rhetorical question)?

Edit/Update: I ended up trying an Irwin/Hanson M10x1.5 hex die. Like @AndyB. said the threads did not clean up like new but they're certainly better than they were. I'll be using new flanged Stover (thread distorting lock) nuts and that should work just fine. Don't forget that these are 38 year old studs and most are rusted beyond use. I consider myself lucky that they cleaned up and are usable.
 
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4x4prepper

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> I was able to determine that the pitch was 1.5 and M10 is the only thing that fits, diameter-wise.
> Why would these studs be something special/weird (rhetorical question)?

google:
"Are m10 and 3/8 the same?
That said, they are very close, the 3/8" bolt is about 0.019" smaller and the pitch's are very close so the 3/8 -16 bolt will thread in the 10mm x 1.5 but the 10 x 1.5 bolt will not fit the 3/8 but.."


But, to make it worse, they are probably pipe thread 🙃

> At this point, is there any chance that they will simply unbolt?

I suppose there is a chance. When I have had to remove them, for various Fords, I have had to grind them flat and drill them out, and then use regular grade 5 or 8, 3/8" bolts in their place. My expensive stud removers get little use on exhaust systems.

There are aftermarket gizmos that will clamp your exhaust on using the remainder of the stud. If the threads are too loose you can always try copper leaf. Or have an exhaust shop tack weld on a new stud over the old one.
 

Bronco648

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They seemed to clean up OK with the M10x1.5 hex die. I haven't tried to hook up the Y pipe but it might work out OK. We'll see.....
 

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