B pipe replacement and rusted nuts

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.
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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.

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catalytics are expensive.

use a nut splitter or a cold chisel to remove the rusty nut,then clean up the stud's threads and use a new nut.If you can get a Dremel hand grinder with a cut-off disc in there,that can start a nice cut for the chisel to finish. (back when Craftsman was tops,they used to make a nice set of thread- chasers to clean up rusty/dinged bolt threads.I have a set for US threads.)
I suspect shops have air-powered chisels,making it a lot easier.
--
Jim Yanik
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Thanks for the responses so far. If I can't hammer the socket over the nut and were to instead cut off the rusted nut and bolt with a dremel tool, would I be able to replace the bolt coming from the cat or is it spot-welded to the cat? The service manual isn't clear, and I haven't yet taken the heat shield off the cat to inspect the cat-side of this joint. Because maybe the bolt should be replaced anyway, since it also apears a bit rusty?
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See if the exploded parts drawings at www.slhondaparts.com offer any insight.

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I was able to complete ths job today, so thanks to all who gave their advice. As I mentioned before, the problem I was having was removing the rusted nuts off the bolts that connect the catalytic converter and the b pipe on my wife's 1995 Honda Accord EX. Here is how I got them off:
1) liberal dose of PB blaster. 2) put on a small nut-cracker that I got from Autozone for 8 or 9 bucks. I torqued the nut-cracker until the chisel penetrated about 3/4 the way into the nut so I wouldn't hurt the bolt. I think this process deformed the nut just enough for the PB blaster to work its way into the threads. 3) finally, I put my ratchet on there and the nuts broke on the second or third hit with a hammer. I know hitting the ratchet handle with a hammer is likely to ruin the ratchet, but I didn't have a breaker bar and the ratchet still works.
An interesting side note, it seems that the nuts are not 13mm or 14mm. They seem to be somewhere in between, as the 13mm didn't fit over the new replacement nuts, and the 14mm had some slop in it. I also tried standard sockets without an exact match. Perhaps they purposely do this so the 14mm socket will "always" fit over the nut even if it is rusted. I guess this is a good design, especially if you are using an impact gun.
Anyway, the job is done, and I saved myself about $100 by doing it myself. Thanks again for everyone's input.
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Nice update.
I tried one of the Autozone nut busters (with the chisel, to be torqued into place) on a lower control arm castle nut this past summer and got nowhere. Maybe my technique is poor, though. The Autozone clerk warned me that it was not guaranteed to work, and I could even bring it back.
I would be surprised if the OEM nut heads were non-metric.
My exhaust system has been worked over so many times (by places like Midas) and then by myself, that most of it is no longer OEM. I have had to disassemble the joint between muffler and cat converter for other jobs a few times now. Getting the bolts and nuts free is easier every time. I do keep a tube of anti-seize handy, recognizing that technically, the torque should be higher when using the stuff.

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Elle wrote:

Yeah, the Autozone nut buster ("OEM" brand) worked insomuch that I was able to get the nut off. But it defintely did NOT "bust the nut"--at best it dented it. The chisel also kept spinning around instead of staying in a vertical position, which was very annoying. Fortunately enough for me what it did manage to to do seemed to be enough for the PB blaster to work, at least that is my theory.
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Perhaps your sockets were not truly 13 or 14mm. I have a couple of different socket sets,different brands,and the "same" size sockets fit tighter or looser than the other,on the same nut.
--
Jim Yanik
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Greg wrote:

It's probably a stud welded to the cat. The best way to do this, given my experience doing exhaust work, is to heat the nut up. Most mechanics would use a small tip on their oxy-acetylene torch. However, you might be able to get by with a MAPP gas torch (just make sure that it's one that puts out a nice conical flame, I've seen some which produce a very diffuse flame which isn't what you want most of the time). Heat up the outside of the nut until it's red and then turn it with a socket. Use an impact type socket or you can risk taking the temper out of a chrome socket and then it could easily break the next time you use it.

With regards to the nut size, Honda usually doesn't use 13 mm sized fasteners. It was probably a 14 mm at one point. I suggest using a special "twist" socket that works great for stripped or rusted nuts/bolts. You can find some examples at http://tinyurl.com/hrp8a and http://tinyurl.com/kg9td . They are worth their weight in gold when it comes to removing rusted or stripped nuts.
Eric
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