I broke an exhaust stud and got it out by welding a big nut onto it. Of course, it galled the head. Perhaps, it was inevitable or I did not let it cool enough or should have heated the head with a torch or melted wax or whatever. At least one third of the threads are gone. A stud would hold in a pinch, but I figure it really ought to be repaired while the head is out. I am down to:
Time-Sert: What I see a lot of and for sale on VW sites. Expensive to get the tool set with countersink. E-Z Lok: Cheap but I keep reading about Time-Sert instead. Seems like the OD is bigger, but I can't find the OD of the Time-Sert. Step stud (oversized on one end): Cheap but I figure it could gall the head should the stud break again.
Which is best?
If my concern of the step stud breaking some day and ruining the head is unlikely, then I will go with that.
By the way, this looks like a very low mileage head. The engine was in a Ghia that has probably changed hands a lot and sat hardly ever run (even less to operating temperature).
TimeSerts and Heli-coils generally use the same size tap, 1mm larger (and the same pitch) as the original thread. TimeSerts make a nice repair, but as you say the kits are pretty spendy for someone who'll only need one every few years - if then.
There are step-studs which are 9mm on one end but they're hard to find - the ones you'll usually come across are 10x1.5 on one end, bigger than they need to be IMO.
Long story short, for your situation I'd recommend a low-end Helicoil kit, since a machine shop would probably charge the price of one for a single repair. They don't come with as fancy of a "shooter" as the industrial-grade versions, but on a small thread like this the simple plastic winder is good enough to get the job done.
A cheap & dirty fix that's sometimes possible is to grind a nut down so it can be stuffed up into the head, and use a stud that's a bit longer so that it engages the nut..but it sounds like this head is too nice for that approach.
