Heat Exchanger and exhaust studs questions 2.4 litre

[billwagnon]

I successfully removed the original heat exchangers and I'm replacing with SSIs.

I decided to try removing the existing exhaust studs to replace with new ones. One broke off and I free-hand drilled it out, but couldn't get everything. Used the Stromski jig which includes a tap and was able to get all the old stud out.

On that particular stud, I can now thread the stud by hand.

For the other studs that did come out, the new ones are very very difficult to thread. I got them all using two nuts but I was concerned about breaking them off. They look like they could go in about 2 or 3 more threads deep.

1. Should I pull the new ones out again, and re-tap the holes using the Stromski tap? I have a fear of ruining the aluminum threads.

2. For the studs that wouldn't come out, should I turn until they break, and then use the Stromski jig to drill them out and clean up the threads like on the first one?

My concern is the existing old studs look original. The engine was rebuilt about 30,000 miles / 14 years ago but I think these are the originals and they look somewhat corroded, like they may be 45 years old.

[Amstaff]

I just finished extracting a few of mine. Best bet is to soak them with some type of rust penetrating spray like PB Blaster for a few days. Then try double nutting them and extracting them. Then, if they break they break.

Just my 2 cents

[billwagnon]

I've done PB Blaster and also used a MAPP torch on the cylinder heads but the heat didn't seem to matter.

Should I re-tap the threads on the super-tight holes?