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catalytic converter

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  • catalytic converter

    A friend wants me to weld a threaded bung to accept an oxygen sensor into a catalytic converter. I'm sure the stuff is galvanized or coated somehow.
    I was wondering if anyone brazes them in, or is welding the ticket. I would be tig welding if I go that rout.

  • #2
    Add the bung just up stream or just down stream of the cat dependong on its use, not into the cat container itself. I don't think there would be a heavy coating of zinc if any on ex pipe. Zinc and many other metals can damage a cat. I have added bungs on a few with no issues. Any method will require you to clean the surface to the base metal so overall it is not a real issue. Welding is prefered IMO.
    Last edited by Vicegrip; 10-30-2008, 06:27 AM.

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    • #3
      Originally posted by Vicegrip View Post
      Add the bung just up stream or just down stream of the cat dependong on its use, not into the cat container itself. I don't think there would be a heavy coating of zinc if any on ex pipe. Zinc and many other metals can damage a cat. I have added bungs on a few with no issues. Any method will require you to clean the surface to the base metal so overall it is not a real issue. Welding is prefered IMO.
      Thanks.
      I think he did mention that it was in a short piece just before the converter.
      I guess I will weld it.
      Last edited by burninbriar; 10-30-2008, 06:50 AM. Reason: Question already ansered

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      • #4
        Cats...

        I have a '96 Jeep that the cat starting making a nasty rattle when you shut it down. I unfolded the seam on the outer cover and removed it, used a grinding wheel to slit open the cat and found the covering on one of the ceramic sections was gone. I wrapped it with an industrial product called fiber-fax and tigged it back together. My guess from cutting it open was it was some sort of stainless, I used 308L filler to weld it back together. The cat itself wasn't galvanized just the outer cover which I replaced and re-crimped the edges.

        I wouldn't think welding in a bung for the o2 senser wouldn't be a problem. Worse issue would be to issue you hit open space in the cat.

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        • #5
          I build a lot of custom down-pipes (exhaust tube from turbo to cat) and high flow cat installs. There are 2 O2 sensors..*at least on a 4 cylinder* One is upstream more to the motor side and reads air fuel ratios for the engine's ECU to adjust delivery to maintane the correct AFR. The downstream one (behind the cat) is just there to make sure the cat is working. If the readings are too close between the 2 sensors the ECU knows there's no cat on the car, or that it is not working and signals a "check engine" light.

          As for welding them.. on pla in exhaust i MIG them just inside of the open garage door, this way I don't breathe the fumes of any coating burning from the pipe. The one exception would be when i do stainless setups for people, then i TIG it because there's no galvanizing or anything like that on stainless parts.

          Hope this helps

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          • #6
            info

            Most newer pipe is what they call aluminized, not galvanized. I've welded lots of it. No fumes and no grinding or cleaning it before welding, just mig right thru it.

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            • #7
              Thanks for all the replies guys.
              The bung is going on the exit end of the cat. I wanted to put it into a separate adapter pipe but the way it is I think I will have to put the bung in the exit pipe on the cat itself and then weld the adapter pipe on. The pipe comming out of the cat is a gold color, like a grade 8 bolt.

              This guy is my best friend and he's really pissed at himself for how he ended up in this position. He was doing this for his daughter and trying to save money. After going through the first car bit for three other kids before her, he knows how you can waste a lot of money for nothing.
              He now wishes he had just bought a whole new exhaust. This universal cat was less than half price of the one that is made for it and the guy that sold it to him said they just cut the O2 sensor off. My buddy bought it not thinking that down here there is no emission inspection and up where he lives that wont fly.

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              • #8
                most aftermarket (if not all) convertors are have a shell of 409 stainless which is a non-austentic and ferritic... meaning a magnet will stick to them.

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                • #9
                  Well, its welded in and everything went alright, the senser screws in OK. I ran compleetly out of argon on this, the gage has been on 0 for a while now, I know what I'll be doing tomaro.
                  Attached Files

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                  • #10
                    Well now

                    That looks better than factory. Good job and I'm sure he'll be happy with it.

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                    • #11
                      Well now put that in your pipe and smoke it!

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                      • #12
                        Yea, that's one pipe no one on this forum can weld.

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                        • #13
                          Your weld looks just fine. I see you decided to TIG it anyway I would have too, now that i have my own that is.

                          Lots of people in no emmission areas will either cut off the rear o2 or replace it with a "jim-stim" (it's an O2 simulator box) Those people are ignorant...even though mine is not used (stand alone engine management system) I still have the wires, sensor and bungs in place so that it all looks factory and i don't go cutting up a factory wire harness <---read: expensive!!

                          what kind of car is it? I install and tune engine management computers, fab turbo and exhaust systems and do some other custom stuff. The one thing i really hate is chasing down factory wiring as there's usually changes within a "series" of body styles over the years it was produced.

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                          • #14
                            I can't remember what kind of car he said it was.
                            There was an adapter I welded on at the end of this pipe also since there was not enough room for a clamp after welding in the bung. I also had to splice the sensor wires back together witch was a pain becouse he cut them right at the sensor. I sure hope the sensor is still good, he said the new one is around $80.00.

                            Thanks for the complements on the weld.

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