Cracked exhaust manifold

Mopar Exhaust Systems

  1. 69swinger340391

    69swinger340391 Well-Known Member

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    Has any one had any luck welding a cast iron exhaust manifold? I have a crack near the drivers side rear bolt on the exhaust manifold on my 69 340 Dart.

    It leaks (ticks) for a couple of minutes after startup until it warms up, expands,and seal the leak.

    I practiced welding a cast iron brake rotor with .030 flux core MIG, and it held up pretty well, but after some hits with a hammer, the weld broke. It was obvious that the weld doesn't penetrate the cast iron. Any ideas on a better way to weld this?
     
  2. daredevil

    daredevil Well-Known Member

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    I have always used a torch with a rosebud tip and a braizing rod. then smoothed it off and used a little black hi temp paint
     
  3. DARTLARRY

    DARTLARRY Well-Known Member

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    The best way to repair it is with an arc welder and nickle rod. Ive seen them brazed with a torch. But the arc welder does alot better job.
     
  4. mplsmyke

    mplsmyke Well-Known Member

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    I also have had good luck with the nickle. V out the crack first.
     
  5. Burntorange70

    Burntorange70 Well-Known Member

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    I welded up a big crack on my manifolds. I just ground the crack a little bigger so the weld had some area to stick to then welded it up with the MIG welder. 4 years latter it is still holding strong.
     
  6. 1970duster440

    1970duster440 Senior Citizen Member

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    The biggest thing is to pre-heat it before you weld or braze it. If you don't it could crack somewhere else do to drawing of heat. If you can get to it drill a small hole at the end of the crack to stop the cracking before you fix it.
     
  7. 62v200

    62v200 Well-Known Member

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    Yep...all of the above. Get the area almost cherry red if you're gonna stick weld it then hit it with the arc. If you're gonna braze it, take your time , do the same thing and then apply the braze rod. Get it good and clean first with a wire brush or sandblast.
     
  8. matthon

    matthon Well-Known Member

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  9. bobscuda67

    bobscuda67 Well-Known Member

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    I had mine brazed. What they did was heat the manifold up to 1200 degrees in an oven and braze it, pack it in sand and let it cool down very slowly over a few days.
     
  10. 69swinger340391

    69swinger340391 Well-Known Member

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    Thanks for all the replies. I think I'll go smash up another old brake rotor and practice with the arc welder.
     
  11. perfacar

    perfacar Well-Known Member

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    hi, the area has to be clean. welding with stick is the best way. use a machinable nickel rod. or there is cast rod now. v out the crack, weld bout one inch, stop, remove slag with a slag hammer, keep hitting on area with slag hammer for bout a minute. when you can touch it without burning finger, then weld another section, repeat with slag hammer. when you pound with a sharp end of a slag hammer, it stress relieves the cast iron. do not heat it before, cast is not a very stable metal when hot. weld at room temputure.
    I 've welded cast this method. exh and blocks, heads. from a pipefitter/welder.
     
  12. Rob64GT

    Rob64GT Well-Known Member

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    I would have to agree an Arc welder and nickel rod, grind a V in the crack and drill the ends of the crack, although I heat the item in my BBQ before welding (350-400 degrees) then let it cool slowly as the charcoal burns its self out. Yum Yum BBQ manifolds no sauce needed.
     
  13. 69swinger340391

    69swinger340391 Well-Known Member

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    I got the nickel rods the other day and practiced on a cast iron brake rotor that I smashed in half. I welded at room temperature, and stress relieved with the hammer afterward. When all was done, I went back to the street and threw the rotor in the air trying to break the weld. After 6 drops, the rotor finally broke, but not at the weld! The weld was stronger than the castiron. Thanks for all your advice.
     
  14. jamesdart

    jamesdart Well-Known Member

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    manifolds are funny to weld. im not aying impossible, but all the heat cycles they go through really changes the cast iron. i like to braze them. for my 1931 essex i had a piece that was completely missing from my manifold where the pipe bolted up it has a 3 bolt flange. once i cleaned it i could see it was already welded with nickle and there were a ton of stress cracks in it. i ground it all out threw it in my bbq at 500, heated the area to be brazed to a dull red and built the entire area up out of braze with a cool flame, nice and slow. i used a ton of braze i didnt really have any choices as the manifold is pretty much non existent. it held up great. i do not like the nickle rod. there are some old timers out ther ethat weld cast iron with cast iron. there is no rod available, they use things like broken bath tubs and piston rings for filler with flux, preheat the shit out of the part to where all of the expanding is done and gas weld it up, heating the entire part until welding is complete. then slowly walking the temp back down. i nthe end you have a part that is welded with machinable cast iron. it has the same properties through out. the last thing you ever want to do with cast iron is mig it. you wind up with a very hard brittle weld that attracts al lof the carbon fro mthe surroundign area.
     
  15. TheCrackHead

    TheCrackHead Banned

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    That passenger side 340 exhaust manifold almost always cracks.
    Torch and rod - mig, all work.
     
  16. 69swinger340391

    69swinger340391 Well-Known Member

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    I used the nickel rod and welded the broken section back on. Vee-d out the crack, no preheating, small sections at a time and let it cool to the touch in between. It's been been back on the car for a few hundred miles now, and the exhaust leak in gone.

    Thanks to all for your advice.
     
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