Nice!
Alternative method for extracting bolt or stud broken in aluminum with less space for all the fancy drilling, and higher stakes of failure (like extracting a broken stud from an aluminum head):
Need: Welder, fender washers, appropriate sized nuts, appropriate tools for removing a nut / stud.
Backstory: At first I was going to not replace the studs because I was scared of breaking one. Then when I was cleaning up the threads with a die the studs were coming out with just the grip of the die backing off, so they all came out very easy, until the last one which broke without warning.
The first time it broke, it left 3/8" sticking out that I was able to weld a nut on, but then it broke again. This was probably my fault the second time, I got so excited it was coming out I didn't take my time and just started going to town on it. If this happens and it starts turning out, take your time, use penetrating lube and drive it back in. Like, 1/4 turn out, 1/8 turn in. Or whatever you see fit. If it starts getting tight backing out, turn it back in.
This picture shows the 3 stages of removal for this stud. The initial break when I had two nuts on it and was backing it out. The second break when I got excited it was coming out, and the final extraction.
As I was mad, I didn't get pictures of the second time it broke. The break left it approximately 1/8" below the machined surface that the exhaust manifold mates to.
I asked a ton of people, did a bunch of research, and found this method. Part of my research was asking a few local shops how they would do it, and actually an older guy at a Midas turned me on to this method. He seemed very very confident with it and said he has used it dozens of times on exhaust manifold studs. He also said if I could get the car to him he would do it for me. He really stressed to just keep on trying, and that sometimes he had to do it 10-11 times before the stud would come out, and since I had already had the stud backing out he was certain it would work. At this point, I was left with the choice of trying this or removing the head and bringing it to a machine shop.
On to the method:
This method involves building up weld on the stud, welding a washer on, then welding a nut to the washer.
For me, it worked on the 6th attempt. The first few times I tried using materials I had around the garage, the last few I went and bought better sized washers and nuts knowing what I had learned from the first failed attempts (1/4" or 3/8" fender washers and 3/8" nuts).
This method helps in that welding the stud will shrink it in size, it also gives you something to build on and get a wrench on in tight spaces where drilling isn't ideal, or possible.
So, set the welder to the appropriate temperature and wire speed. Do a quick (2 seconds or less) circle around the center of the stud to start a little puddle. While the puddle is still hot, tamper it with a hammer or a flat punch and let it cool. Repeat, running the stinger in circles and continuing the pile about the size of the stud until it is protruding enough that you can get a washer on it. Extend the puddle of weld outward to the washer to fill the hole of the washer.
Once you have the weld built up, the washer welded on, and the gaps between the washer and the weld built up and filled in, you then weld the nut on. I found it was best to weld 5-6 spots around the outer edge of the washer and then weld in the center of the nut. Let it cool, attempt extraction.
As I said earlier, when it starts backing out take your time. I used a 1/4" ratcheting wrench and the appropriate short socket, so it was more sensitive to movement and wasn't so bulky and you could tell if it was about to yield. Use loads of penetrating lubricant, back it out, if it starts getting tight, lube, drive it back in, back it out again until it gets tight, lube, lube, lube, heat. (I had a friend holding a torch in the exhaust journal pointing towards the stud)
Shaky, blurry, excited picture of the success! As you can see, the weld will puddle to the aluminum but not bond with it.
Then you can chase the threads, put in the new studs.
