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)

[913B]

ok, so I checked it again, appears the depth of hole is deep enough for the following ez lok. I think I will go with the standard external threads thinking easier to get the drill bit. I put the 27/64 drill bit in my hole and it looks like it barely have enough meat for it to clean up, but it will not go in the hole without drilling. Is this a good indicator I have enough meat for the ez lok ?

The next important part is drilling/tapping straight. I know it is VERY important, can I rent or borrow anyones jig or fixture they have made. I promise not to damage or will pay you for it. If the tap is crooked, am I all lost, is it still possible to tap the stud straight with mallet or something. Of course I am going to eye ball the best as possible. Any reccomendations and experiences to share ?

Once I buy a good quality 27/64 bit from Home Depot or whatever, I'm kinda scared of the HF one. HSS is good right no need for cobalt I think. I am going to turned it down in my friends shop so I can chuck it in my 3/8 drill and not have to man a heavy 1/2" drill under the car.

Anyone, anyone I can or borrow your jig/fixture to drill straight ?

http://www.ezlok.com/InsertsMetal/SSthreads-uncExternal.html
P/N 653-8
Internal thread M8-1.25
External thread 1/2-13
Length .484
Tap Drill 27/64
Tap size 1/2-13
Min Depth 9/16

Thanks All !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!