Exhaust Stud Heli Coil Pulled Out, Wou is me, Help! Correction Time Sert came out Options

[913B]

So the continuing saga of fitting the SS heat exchangers continue. I somehow pulled out the heli coil repair on the exhaust stud. The coil measures 9.5mm OD.
I suppose I need to re-tap the hole with a step stud.

So what size step stud should I use ?? M8 to (M10 or M11) ?
Where would I find such a stud ?
Is it do-able, drilling and tapping from under the engine ?
How the heck am I going to keep the bit and tap straight and not F/up ?

Man it never ends with old cars...... (IMG:style_emoticons/default/ar15.gif)
Thanks in advance for everyones help !!!! I really appreciate it.
(IMG:style_emoticons/default/beerchug.gif)

[HAM Inc]

Because of the proximity of the ex seat to the stud boss simply welding the boss and remachining (which needs to be done on a mill on a fixture for accuracy) is not a good idea. The welding causes distortion to the seat counterbore and can/likely will lead to a dropped valve seat.

The right way (and the only way I approach this situation) is a total remanufacturing of the heads. Anything short of that is patch work. Doing a little work here (welding) and a little work there (replacing one valve seat) but not doing a complete job will have you revisiting other issues at some point in the future.

Once you make the decision to pull the head, my advise is to pull both. Have them properly gone through, put the thing back together and don't worry about head issues for a very long time.

There are shortcuts and many people have tried them. Some have gotten lucky, many have not. You have to ask yourself, "Do I feel lucky?"