Exhaust manifold to catalytic converter nuts and studs rust welded

[FireFox31]

I attempted to remove the studs from the manifold in the car. I was able to remove two studs using the two nut trick. I had cut the third stud too short and mangled the threads trying to get two nuts on it. I may use a die to cut smaller threads then use two smaller nuts. The fourth still has good threads but I can't budge it with reasonable force, blow torch, and oil. I will try inductive heat and maybe see if someone can help me with the oxy acetylene torch.

The good thing is I only need one working stud to somewhat hold on the cat pipe, so I'm twice as barely good with my two new studs. I may switch to installing the used cat and new muffler, worrying about the final two manifold studs later. I think the gaping hole in the muffler is causing more noise than the slight gap in the manifold to cat mating surface.

[kcodyjr]

Just to add a side of fries to this excellent discussion on how to deal with hopeless levels of rust.

The penetrating oil you want for tasks like this is called Kroil. It comes as a straight liquid, or as a straight aerosol, or as an aerosol that also deposits silicone lubricant after it evaporates. This stuff makes PB and WD look like spilt soda pop.

[FireFox31]

Yes, Kroil is what I'm using. I believe it's aerosol without silicone. I would heat the parts to hopefully introduce some expansion and gaps, then spray the hot or warm parts with oil. Wear a respirator because a lot of oil will immediately vaporize. I hope some oil worked its way in despite that. I believe that many applications of heat and oil really helped

I have a followup to this thread which I haven't had time to post. I bought some new tools for the job which removed the remaining studs with ease. Maybe the heat and oil loosened them up, or maybe these tools are truly amazing. I'll post it all at some point. Don't play around, get good tools, even if they're only for a single job. I would have saved many days of work if I had them first.