Here is my saga a few months ago.
A friend starts having a strange Putt-putt noise on his engine. Turns out that there is a broken head stud on lower outside #1. Yep, His 83SC had lower dilivar studs
Next thing you know, the engine is out of the car, heads are off and we are pulling studs. Using the usual method of heating the case spigot by the stud using the Oxy Acetylene torch is mostly working. We managed to pull 9 of 12 lower studs with no problem.
One of these remaining was the initial broken stud. I tig welded a nut to the top and with a little heat it came out easily.
Remaining stud #2 broke about 1 cm above the case spigot. Enough room for a welded nut. Again, the tig welder to the rescue, or so I thought. The nut welded easily enough. Then after some heat, the stud started to back out. Next thing, Snap. The stud broke clean below the newly welded nut. I guess it was really time to get these out of the motor. Dilivar bad
This remaining stud material was almost level with the spigot. Time for plan B. Grab a bolt, clean the end. run a TIG bead around the base with no problem. This time, more heat and the remains succumb to a CCW rotation. Yep, out at last.
Remaining Stud #3. Of course, the last stud is the worst. We started with the OA torch heating the spigot. With the double nut on the top we started to turn it out. It went about 1/2 turn and then broke level with the spigot. I thought there was enough room for a nut. I welded a nut. The tiny filler I added to the middle of the nut ran down the side and into the recess in the spigot formed by the diamter of the hole. Crap. The nut held but I could not turn it as it hit the case. We tried anyway. The stud now broke clean at the nut, just like #2. I got a bolt out and started to weld. This stud would not take a bead no mater what I tried. It just would spit and sputter and not melt. I finally got a bolt welded only to have it break off. AFter several cycles I thought we were done. We started getting out the phone book looking for EDM. I thought we would try one last thing.
Drilling these studs is next to useless. Yes, we tried this too and broke 3 bits. Crap.
Using the dremel cleaned up the stud remnants. By this point they were flush with the case. I then laid a bead of weld on top of the stud forming a mushroom. The TIG filler is soft and allowed us to center punch and then drill a small pilot in the soft material. Next we started grinding with the Dremel and a carbide cutting bit. After about 45 minutes we milled down 8mm using small circular motions. This was deep enough for an extractor.
We seated the extractor with the hammer and began heating. The entire case was so hot we could not touch it but stud finally backed out. Victory at last.
Here is the carnage.
For reference, here is the carbide cutter that actually managed to cut the dilivar stud. I was not hopeful when we started but was ecstatic at the end results.
What a fun way to spend a Saturday. Wrenching and burning metal.