I've already rounded one of the nuts on the exhaust manifold to Y-pipe studs. I think the nuts are probably 14 or 15mm, but I don't remember exactly. The flat ends of the studs are about 6.3mm (1/4"). I want to just replace the studs and nuts completely at this point with the nuts and bolts that came with the new exhaust manifold gaskets I got. I know there's a trick where you use new nuts to break a stud free, but I think the studs might have metric threads, and all I've got is a key-type SAE thread checker. I've got a different metric thread checker set, but they're the closed-end type, so they're not deep enough to reach the threads of the studs.
I could buy a deep-well socket extractor for the rounded-off nut and just ignore the stud, but I'd still have to get a new nut that matches it. Since the end of the stud is flat, and since there's not enough room in there to fit in needle-nose vice grips (assuming that even then they'd give me enough grip and torque to break the stud loose), I think the two-nut method might be the only way to get it out, but even then, I don't know if it'd work due not having room to fit a wrench up in there (if I recall correctly).
All of this is related to getting rounded-off and seized o2 sensors out and not having enough room to fit extractor sockets on the passenger-side one. I don't think disconnecting the Y-pipe end would let me lower the Y-pipe enough to get the tools in there. At some point, I expect I'll have to replace the exhaust manifolds, so even if ignoring the exhaust manifold studs now is feasible, I'll have to disconnect those someday.
I could buy a deep-well socket extractor for the rounded-off nut and just ignore the stud, but I'd still have to get a new nut that matches it. Since the end of the stud is flat, and since there's not enough room in there to fit in needle-nose vice grips (assuming that even then they'd give me enough grip and torque to break the stud loose), I think the two-nut method might be the only way to get it out, but even then, I don't know if it'd work due not having room to fit a wrench up in there (if I recall correctly).
All of this is related to getting rounded-off and seized o2 sensors out and not having enough room to fit extractor sockets on the passenger-side one. I don't think disconnecting the Y-pipe end would let me lower the Y-pipe enough to get the tools in there. At some point, I expect I'll have to replace the exhaust manifolds, so even if ignoring the exhaust manifold studs now is feasible, I'll have to disconnect those someday.