Exhaust Studs Broken.., need suggestions. Options

[DougC]

OK, I have 3 broken exhaust studs on my 2.7 six. All but these three came out easily but these 3 were never going to move! I spray (for several days) with PB blaster, used a torch and nothing worked. Finally I bent one on purpose because I was at my wit's end and eventually broke it. I went ahead and cut the other two off in preparation for drilling. I have drilled out the originally broken one and tried using an "ease-out" but no luck (of course). I'm at the point where I can actually tap the hole for the original thread size. What size tap do I need to buy?

Doug C

[Sammy]

Two ways to do it, one is electronic discharge machining as mentioned.
The other is to make a machining fixture that guides the drill perfectly.
A jig like that is darn near fool proof and even allows drilling out the broken stud with the engine in the car.
John Walker up in Washington does it that way, I think TRE in Hollywood does too.
The trick is to machine almost all of the bolt out getting as close to the root diameter as possible without going into the aluminium. Then it is just a matter of peeling the threads out of the hole with a pick or something.
Don't try it freehand or you may be in the market for a rebuilt head.

Might want to do a search on the pelican 911 technical board, maybe even post the question. There are several guys on that board who have done it correctly and successfully, they may even have a sketch of the jig. Lots of very experienced helpful folks over there. They may be able to save you a lot of money, time and aggravation.
Just don't mention anything about car wax, CWs, or small winkies. They don't like people who ask for advice and insult them at the same time.