Cat-converter mounting flange replacement/work around

Hi all!

Let me just preface this by saying that I'm stubborn, so as to head-off the "take it to a shop, it's cheap" comments. I want to do this myself, because that's how I learn and get better at fixing my vans!

Anyway, I'm replacing the cat. Got a bolt-in replacement on the ebay for $65, so am doing pretty good so far. Problem is that the rear bolts are rusted on tight and no amount of penetrating grease is going to do a thing. Luckily, the front bolts came out without too much effort, so I was able to get the cat - plus about 4 feet of exhaust from the cat back to the muffler, out from under the van in order to work on it. In the light of day it was clear that it's too far gone for conventional removal. So I got out the grinder and took off the heads of the bolts. Success, the old cat is now removed from the exhaust but for one part: the flange that holds it all together. Hopefully this makes sense, but if not, it's got the nut/threads for the mounting bolts built-in to it, with a small flange at the bottom to hold the cat in place. It's a very secure system, and I'm specifically wondering how integral it is to the integrity of the joint?

So, to be clear, the issue here is that the remnants of the mounting bolts I ground the heads off of are rusted into the threaded-nut portion of the mounting flange. In fact, most of the flange itself is badly rusted - and though I could do something drastic like try and drill out the center of the bolts and chip away at it from inside, I sincerely doubt the threads would be salvageable and would also suspect the metal itself to be compromised and weakened because of rust.

Long story for a short question: Why can't I just buy 2 bolts and washers and strap the cat in there minus the flange? And if the answer is that the flange is integral, where can I get one, or more likely, any ideas for a DIY work-around?

Thanks for any input, drive safe out there!

Pictures would be very helpful as I can't quite invision your suggested work-around. Typically rusted bolts will usually come out if heat is applied. If focused correctly heat expands the outer material more than the bolt and will usually soften the rust and material that's making it seize. A portable propane torch wouldn't get hot enough, but acetylene/oxygen will. If you don't have access to an acetylene torch outfit there might be cheap alternatives, but I'm unfamiliar with what those could be. Regardless, you'll need to get the threaded part of the flange glowing red (focus heat on flange, not the bolt). Once glowing, assuming you have enough bolt to grab onto, you should be able to remove with vice grips or a stud remover tool.

Tim's right about the pictures.

On a side note, generally speaking, at least from the factory, there would be nuts welded to the back side of the flange (pipe side) so cutting the heads off wouldn't help much in that case, cutting the welded-on nuts off the back side of the flange, will usually allow one to install a standard 10mm nuts and bolts to provide appropriate clamping force on the flange.