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Originally Posted by guage
I'd feel a whole lot better about doing this if I could just get
that stud center punched before try'n to drill it out.
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I just removed 3 studs from M117 aluminum heads I am working on. Drilling into the exact center of the stud is absolutely critical especially in aluminum heads. If the drill goes off center it will break through the stud and take the path of least resistance into the aluminum at which point its pretty much FUBAR. I have also found that stud removers are pretty much useless and usually break and leave a hardened piece of metal in the center of the stud, once again a FUBAR deal.
Fortunately I have the heads off my car. To aid in drilling I made a drill guide out of a steel block. For 8mm studs I find a 1/4" drill bit works good. I drilled a 1/4" hole in the steel and another 5/16" hole that aligns with the opposite stud hole. I bolt the plate to the head and align the 1/4" hole over the broken stud. I apply a little superglue to the edge of the plate to help keep it from moving. I then drill out the stud using a sharp 1/4" drill. Once the stud is drilled I go in and remove whats left of the threads. Sometimes I can pick out a strand of thread and pull and it spirals out of the hole leaving nice clean threads. I finsh up by chasing the thread with a tap which removes any remaining thread material.
In the case were you still have the heads on the car I wonder if there is any way you could use the exhaust manifold as a drill guide. Go to a hobbly shop and buy some 5/16" OD brass tube with a 1/4" ID. You can use a short piece of tube to center the drill in the manifold. I don't know if you can get the clearance to do something like this. One thing I do know, trying to just drill out a stud unguided with a drill will 90% of the time result in bad news... You feeling lucky???