Try the penetrating oil "PB Blaster" first. Around $4 for a
large can at places like Autozone and Wal-Mart. Soak for at
least an hour. Repeat application. This, with a large
breaker bar and/or a hammer applied to the wrench end, has
worked on every exhaust system nut/bolt I've had to remove
on my 91 Civic, from those at the manifold to those on the B
pipe.

You can't get any socket over the nuts? Try a little
persuasion with a hammer.

A compressed air driven angle die grinder ($6 to $20 at
places like Autozone, Harbor Freight, Pep Boys) may also be
used to cut such nuts off. Get a "cutoff wheel," not a
grinding wheel, for it. Of course this assumes you have a
half decent home air compressor, say 100 psi at 4 CFM. Try
to cut in a direction that loosens the bolt or nut. I have
had a lot of success with this on the tricky control arm
bolts and nuts.

A lot of people recommend applying heat with a torch. Check
the archives for more on this.

"Greg" <centaur99@gmail.com> wrote
> Hello. I have a 1995 Accord Ex (F22B1) that needs the B
> pipe and
> muffler replaced. I have the required parts and gaskets,
> but am having
> a problem removing the nuts that connect the existing cat
> and B pipe.
> The nuts are substantially rusted, and I don't have a
> metric or
> standard socket that will fit securely over it. The nut
> appears to be
> 13mm, but the rust is preventing the socket from fitting
> over it.
>
> So, what is the "standard" procedure for removing these
> nuts? Muffler
> shops must deal with this every day. Most of the rusted
> bolt/nut
> threads I've read seem to either say "cut it out" or make
> the
> assumption that you can get a good socket over the nut or
> bolt head.
>
> If I can't figure this out I think my only option would be
> to replace
> the cat and B pipe as a single unit since I can't seperate
> them.
> Hopefully someone with experience can help me out. Thanks
> in advance.
>