My first tap... http://forums.pelicanparts.com/porsche-911-technical-forum/597019-time-serts-rescue.html

Just use a Big Serts to fix one of the POs making the TX mount 14mm after he F.U. the 12mm hole.

Helicoil can cause studs to not be perfectly vertical from the spigot face. This can cause other damage...

Ok,

Picked the engine up from the machine shop today.

The photo of the stud in the first picture turns out to be the end of a broken drill bit! That's why it was so hard to drill it out and why weld wouldnt stick to it very well. It took the guy ages with numerous drill bits to finally drill it out.

He wouldn't touch the three remaining studs as he said the metal was now very brittle and would break off.

I'll try the welded-on nut trick over the weekend and see what happens.

G.

Use heat...and lots of a good fluid.
I would try to go through 2 or 3 heat/cool cycles to break them free...before trying to turn them.
If you do go to the heat the block method...try some instant freeze (electronics store) on the stud when the case is hot....the temperature differential will help.
Bob

If you don't want to risk screwing up the block at this point (machine shop couldn't extract them), find an EDM machining service. Not DIY, but less drama.

Sherwood

The welded nut trick worked! Very happy.

I simply put a blob of weld directly onto the end of the stud to ensure it had got a good hold, then welded a 17mm nut to that. - easy. I dont know what all the fuss was about. If an IT geek can do that, why was an engineering shop so afraid to try?

Anyway, all the studs are out now. Next - get the case apart and start cleaning/measuring.

G