Broken heat riser and exhaust studs

[CadillacRob]

Well I was gearing up to paint my manifolds for my rebuilt 365 and the studs for the heat riser each snapped, as well as the heat riser itself. 

The studs have no threads.  I have tried heat with a propane torch, oil and vice grips, candlewax, I even welded nuts on and one snapped off the nut when hitting the wrench with a hammer.  I think the last resort here is to cut and drill them out unless there's any other suggestions?

[C Gorgas]

 Two suggestions: Remove the manifolds so you can get at them then drill out the bolts and put in new threads with a tap or, locate another set of manifolds. It is hard work one way or another. Chet 25441

[TJ Hopland]

If you still have stud sticking out the welding nuts doesn't help because the heat doesn't really get into the threads. 

Propane may not get something as large as an exhaust manifold hot enough to break that rust bond.   Know anyone with oxy acetylene?    IF there is still enough sticking out to grab onto I would much rather heat it than drill.   

[Chuck Swanson]

A good machine shop should be able to get them out.  Worth a shot to ask.  I have had a few items that I didn't want to risk ruining, and each time, my local machine shop got them out, for less than acquiring another part.  (For example, using a good drill press, with part in vice, etc..)  Chuck

[carguyblack]

As another Chuck to the mix, I concur with the machine shop idea. I've had impossible miracles performed by those guys and they act like it is an everyday occurrence. No big deal, they say.
By the way, I have a good heat riser (if what you're talking about the wrapped tube that goes from the manifold to the choke)
Chuck

[fishnjim]

You'd be stuck too if you were that hot for that long.  Somethings just don't come apart after they've been through the fire together for so long.
If you don't have the time, tools and skills, => machine shop.   
There's no threads where it goes inside the heat riser.   Those heat risers are notorious for breaking, and most remove, if not concours.   Just lengthen the exhaust pipe on one side.   It's a restriction too.   Getting difficult to find good original ones.
Hitting a wrench with a hammer is not recommended practice and may have had a poor weld.  Use a socket and breaker bar and rock back and forth.   Steel looses its temper after repeated heat cycles, so becomes soft.   I had to drill one on my spare set, it kept twisting off until nothing left, and easy out didn't budge, so it's not uncommon.   Sometime drilling with the reverse drill bit heats it up enough and they come loose, but that's a one in ten shot with rusted threads.   
Too much heat on old cast is not good either.   Get it red and stop, repeat.  If it gets white or surface liquidy not good, you change the grain structure sets up for cracking.   
The internal threads may be damaged if it's really rusted together.   Sometimes you have to go up one thread size, if there's enough metal or replace.
An old trick is to not replace with a black stud but replace with a plated bolt.  Won't "rust weld" and easier to get out.   Some won't accept bolts, depends on the manifold/pipe angles.   Some you can drill completely through and bolt and nut.   Then you just cut it off, next time.   They should've been designed that way.
My one thing leads to another problem theory of "restoration"...

[carguyblack]

Sorry, my bad about the definition of the heat riser. I was thinking of the manifold tube up to the choke. The "heat rises up to the choke to open it". There, now I'm not quite the goof you must have thought I was.
Same advice on the machine shop idea, though!

[CadillacRob]

Good news guys.  I got it. 

Propane torch on stud, heated for 1 minute, then spray with a bottle of water to shock it.  Repeated this a couple times, put a wrench on the welded nut and gave it a few light hits with the hammer, then pulled back as to tighten.  Working back and forth with oil finally got them out. Very surprisingly, no thread damage at all. 

I should note, these are actually replacement manifolds from a friend's parts car as mine were rusted through if you can believe.