Removing Exhaust Manifold Bolts?

The method I have used without fail is what TimGr described, using an Oxy/acetylene cutting torch heat the broken stud to cherry red and give the torch a quick shot of oxygen, this can be repeated until the hole clean enough to pick any slag out. I usually run the correct tap drill in the hole to ensure it has nothing remaining to prevent tapping. Run a tap in the hole to clean the threads, blow out with compressed air, voila you're done!
If you don't have a OA torch, you probably know someone who does. If you are worried about cutting the cast iron with a torch, try cutting a scrap cast iron part with a torch. I used this to remove a broken exhaust manifold stud in my sons' '55 CJ5 F head. Been using this method for 40 + years. Good luck

 

Will this work with a stud broken off flush, or below the surface of the block? It depends upon the stud being much hotter than the surrounding cast iron.

The rear-most stud on my '56 f-fead is busted, but to drill it would require pulling the engine for access, due to the firewall interference.

 

Place a flat washer centered on broken stud and weld it to the stud, then weld a nut to the washer. While hot hit with good penetrating oil (kroil) and as it cools try removing with a socket or box end wrench on the nut you welded. I've found it helpful to use box end and apply pressure a give it a few moderate raps with a ball pein.

 

I have a left hand drill set, be very careful to center punch the very center of the stud. Use the smallest drill you have and drill the center of the stud. After you drill the stud, heat it red hot and let it cool. Shoot it with PB Blaster or something like that. The heat will expand it and when it cools it will shrink then it should come out with the next size left hand drill bit. EZ outs never work, they expand the stud and break off then it's off to a machine shop. Take your time and be very carful and you will get it. Good Luck

 

This works. I did about 20 of those on a flathead V8. Even then, some broke more than once...

 

Do this but add canning wax while hot it creeps in to the threads 99 percent success rate this way for me.

 

When you get all of them out, replace with studs and use brass nuts, they will not seize on the stud

 

PeteL, It will work on any broken stud or bolt, sticking out, flush or below the surface. Try it on a scrap piece, it can be repeated as necessary.

 

Sometimes the bolt head seals so well that penetrating oil wont creep as far as the threads. I have occasionally ground away bolt heads to allow removal of a part, leaving behind a protruding bolt remnant. Then you can get PB Blaster right onto the thread junction. Then work on the bolt with a few heat-cool cycles, more PBB, lots of time, and weld a nut to the stud if needed.

I realize its too late for that now.

 

I finally got around to this after a deployment to the CA wildfires. After many attempts of heat and cool cycles and pb blaster and welding nuts on, that never budged and the wax thing. I decided to attempt blowing one out as suggested by wasillashack. This kinda worked and didnt damage the threads but I had to very slowly work a 3 tap system of removing the debris going back and forth with the different taps. The other two, (total of three to remove) I drilled out with left hand bits to the threads and cycled the three taps in and out until I got all the debris out. Time consuming but I got the new studs, gasket and manifold installed. Amazing to me how entrenched these were in the block, despite the amount of heat applied.
Thanks for all the suggestions, I really appreciate it!!!

 

Thats amazing that you made it happen! Awesome!!!!