I hate doing exhaust work because of the possibility of rusted nuts and bolts breaking, as well as the crampted quarters under the car, but I've got to do it or be ripped off.

I've got to replace the pipe between the exhaust manifold and catalytic converter - the one with the piece of woven flex material in it. I've already purchased the pipe and two gaskets.

This post is part of the planning process.

The pipe in there now is original to the car, so almost 21 years old, and the woven material is now leaking pretty good.

I'd really rather not replace the stud bolts in the exhaust manifold flange where the new pipe will connect to it, so that means getting the old nuts loosened without damaging those stud bolts.

I have a propane cylinder, but the thing takes forever to heat nuts of that size and they never really get even red hot and many times in the past bolts have broken, etc.

I've never used MAPP gas, let alone the small MAPP + oxygen set-up that is currently available from Bernzomatic.

Does either MAPP by itself or MAPP + oxygen really work better than plain old propane for this application?

Do you have any other advice about replacing this particular piece of the exhaust sytem?

Thanks for the information.

 

I'm not familiar w/ MAPP or Mapp+O2, but I recently replaced everything on my 94Ex from catalytic converter rearward. I did use heat on the nuts, PB Blaster, and both seemed to help. However, I did not have a lot of corrosion and I know in areas w/ salt on the roads, the situation is much different. To give you an idea of level of corrosion, I did not have to replace any fastners.

I agree this job is no fun. I spent most all of a day underneath my 94EX. Wrestling those pieces into alignment single-handed is tough. I don't like the spring-loaded bolt combinations as they are just short enough to make getting the nut started barely possible.

New gaskets at each joint are essential.

good luck

 

Ive replaced the spring loaded combinations with stainless on mine. I think I used a 1/4 stainless bolt or 5/16 with a steel coupling that acts as the sleeve going through the joint the steel spring and then a stainless nut, some washers as well. Works very well Ive had them apart several times still have to replace the gasket but they unbolt very easy. The coupling or spring dont rust much and the threads stay intact.

My experience with the bolts is that they were so rusted even when I got the nut off there was no bolt underneath to actually hold anything after the nut came off!! This was on a 96 in the rust belt after probably 10 years. The studded bolts on the cat I re-threaded as they were a little bigger.

Good Luck (sorry my post probably doesnt solve your problem)

 

Well, misery loves company and there are at least two people here who sound like they're as miserable as I am when I do exhaust(ing) work. I just love it when I'm squeezed under the car, looking upward and reefing on some fastener as the rust falls down on my face.

But back to MAPP. Anyone using MAPP to heat nuts and bolts and, if so, how's it compare with standard propane?

 

I've used MAPP in a "normal" propane torch. Not with oxygen. It burns hotter, but the torch itself controls how fine of a flame you get. You probably want a smaller, hotter flame so you heat the nuts but don't overheat the nearby manifold. The difference in MAPP vs. propane is not tremendous. Air vs. oxygen (regardless of which fuel) is a much bigger difference.

I've gotten those manifold nuts off after soaking in PB Blaster overnight. One thing seems to help is clamp the nuts sideways with a visegrip pliers. This flexes the nuts just enough to fracture the corrosion and allow the PBBlaster to soak into the threads a bit better.

That's sorta how heat works, as long as you're heating the nut much faster than heating the stud. You may have better luck with a little micro-torch (butane?) because the flame is so small. You can more easily prevent the heat from playing over the exposed end of the stud.

 

Fantastic suggestion, Jim! Clamping and unclamping vise grips on the nut should in theory do exactly as you suggest. The problem is the access of the vise-grips to the nuts, but this can be improved by "simply" griding or cutting away excess old pipe or pipe-flange from around the nuts.

After soaking in PB, I indend to use an impact wrench on the nuts which will be set on low pressure in order to "bang away" on the nuts more gently than instantly trying to remove the nuts and quite possibly breaking the stud instead.

Thanks again, Jim. At least I now have some hope that doing this job many take an hour, or so, rather than a day.

Since I'll be saving quite a bit of dough by doing this job myself (as usual), I might spring for that Bernzomatic MAPP+O2 setup for this job and have it in the tool box for any future job that requires nuts to be heated. Speaking of heating, if the nut is heated say close to white hot and then allowed to cool, should an attempt be made to remove the nut while it's still hot, or should it be allowed to cool a bit first? After heating, is the stud bolt far less likely to break?

 

You may be able to get away with a hammer and a sharp cold chisel to split the nuts. Even better would be an air chisel that so the nuts can be "walked" around the bolt. Take the nuts off hot if you use heat.

 

I guess I wouldn't go white-hot just because I don't want to anneal the stud underneath. Even if the nut is barely glowing, it probably moves enough to do the fracturing you need.

OTOH, if you start the stud loose from the manifold, then you can replace the stud easily. What you don't want is to break the stud. So don't heat the stud enough to anneal it.

Cutting wheel in a Dremel might allow you to put a slit into the nut. Then take a screwdriver & pry into that slit. Even without slitting all the way into the threads, that can also flex the nuts and improve penetration of PBBlaster.

 

Thanks Jim and Roader.

 

Anyone tried this method and, if so, what did you think?

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