How to extract mangled manifold stud?

[FoxFivePointOh]

Don't screw around with it at this point. Pull the engine and weld a nut to the stud. If you attempt to drill it out with the engine in the car, there is a good chance you will end up drilling in at an angle. I messed up a head on a different car that way.

Drilling should be your last resort.

[Phoenix///M3]

Ouch, if you attempt to drill it use a good cobalt bit (Dewalt, Bosch). Cobalt goes through anything like butter. Might be able to be done with a right angle drill but I would vote against that. I would consult a good machine shop and get some advice.

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[sapote]

Has it been soaking in penetrant? You can try heat too. Maybe drill a hole, perpendicularly, that's half the diameter of the stud and slot an icepick or punch and use that to turn it CC? Hole would need to be large enough to accommodate a piece of metal rod (or icepick or punch) that's not so thin that you just end up bending it.

Its worn shaft is too small for this method.

[sapote]

So.....I broke it, basically flush. Is this an engine out situation?

Sorry to hear this bad news. I was late to this thread otherwise to would suggest to use a medium hammer tapping on the stud head into the head. Patient and time will loosen the threads before trying to wrench it out.

Time to get the cylinder head out and work safely outside. If the broken stud still protrudes a little, then use a dremo to cut a slot for screwdriver but use an impact driver and hammer it to turn CCW.

Currently I'm in the similar work: The earthquake in Socal couple weeks ago knocked my water heater tank enough to crack a rusty cold water 3/4 NPT galvanized pipe threaded to the tank. There is not much for the pipe wrench to grab on the crushed pipe now, so I am cutting a line inside the short pipe and then fold the cut pipe inward to release its threads from the tank female threads. This is like a prisoner cutting the jail bar.