I've been trying to unbolt my passenger side (clogged) catalytic converter for about 3 evenings and made absolutely no progress. There are 2 studs in the flange with two 15mm nuts viewing from the bottom. I had soaked the threads in PB Blaster overnight three times, won't budge. Tried using propane torch on the nut, still doesn't move a bit.

I've got my breaker bar on it and I'm using so much torque already that the stud will either snap or more likely the nut will round off.

Questions:

1. Any other tips for removing the nuts other than PB Blaster and propane? Will MAPP gas help?
2. If the stud breaks, how difficult will it be to remove from the manifold?

Thanks!

 

I have soaked rusty bolts with PB Blaster then smacked them with a hammer a few times. That seems to works well.

 

You need more heat like red hot and then try again. You should replace them if that bad, you just dont want to snap off the studs in the manifolds. That would suck

 

X2. At least you stoped before snaping them off. An oxy acetyene torch works wonders in cases like this.....as long as nothing catches fire!

 

Smoke wrench is the way to go. A little heat is wonderful.
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Yeah, the oxy torch used by an expert is scary & amazing. Had a cat changed on my previous car and watched with interest. I think it's such a vast amount of very localised heat that it snaps all the rust bonds.

It wasn't too expensive to get the work done and it's beyond what I can do - or want to do.

 

What everyone already said.

P.S. Focus the heat on the nut, not the stud. The heat expands the metal allowing you to break the galvanic corrosion bonding them together. It also weakens the temper allowing you to break any burrs that may have seized them together as well. Like Brutal said, when you take the heat away you should see it glowing faint red.

 

+1 For sure it's the nut - you're trying to get as much heat into it - but not the stud - so it expands faster and more thus breaking the bonds. (You have to get some into the stud, but it's a side-effect not the goal.)

The oxy is great because it emits vast heat and fast.

 

Thanks guys, I'm going to look for that MAPP gas cylinder which supposedly burns at double the temperature of propane. With propane I cannot get the nut glowing red hot.

 

Just be aware that might not get hot enough either. I used a propane torch before I got my Oxy-Acet setup and never had much luck with breaking anything free. After I got the big rig it was just a matter of minutes to loosen nuts and bolts.
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MAPP is hotter, but from the sounds of your issue, it won't be hot enough. I have a MAPP setup and it doesn't quite cut it for really stubborn stuff. You probably need a full blown oxy-acetylene torch.

 

Amen! You need to take that to someone with oxy/acetylene and watch in amazement as someone that knows what they are doing gets those nuts right off, just like JagV8 did.

Cheers,

 

There is nothing wrong with PROPANE but the addition of OXYGEN is what is needed.
I use acetylene for welding and some cutting but OXY/PROPANE will braze and solder. It will also heat ALMOST as well as acetylene. I have an old propane tank that I interchange with my acetylene regulator (they have the SAME left hand threads) because propane is a little cheaper than acetylene.

OXY/PROPANE is useless for welding but it heats well for less money if getting something hot is all you need.

Just a thought.

bob gauff

 

Anyone who's never had oxy (etc) cylinders and is thinking of getting them - please research carefully about safety issues (what you must and must not do). Especially oxygen has issues which go well beyond the obvious.

I know mechanics appear to treat these things casually but looks can be deceptive.