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I'm a bolter but I have another vehicle that I am also working on for which there is a relative scarcity of parts and am looking to my fellow bolters for some advice. I have broken the threaded ear off my exhaust manifold that bolts the exhaust pipe to the manifold. It's half off right now and holding with a nut in place but it's a precarious perch. I saw a post where a guy seemed to have some expertise in welding/brazing cast iron. I have not had much success doing that in the past. In my experience, cast iron cracks right after I try to weld it. I have a torch a stick welder and a mig welder and have done gas brazing. What is the trick for welding/brazing cast. I have the piece that broke off but fear making the problem worse.

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orchidskip,

Everyone has strong opinions on welding, especially cast iron. I have done it many times using different methods. This is what I would do, other will say 'nay', do it this way! Take my advice and suit yourself.

Make a flat plate so that the one good ear/bolt will hold the broken ear in the proper position. You could even have another bolt in the fixture plate to hold the broken ear where it's suppose to be located.

Bolt everything up with the fixture plate on the bench where you can get to it. Use your MIG to make two small tacks at each end of the ear to hold it to the broken manifold. Remove the fixture plate.

Using a die grinder, 'V' out the crack on both side, almost to meet itself, but not quite. The MIG tacks will still be holding the two pieces together. When you have the die grinder out, buzz it over all the adjacent areas to knock off the rust and junk and get down to bright cast.

Use a large welding tip and flux coated brazing rod, and as you heat the area to a dull red, bring the brazing rod into the flame and let it melt and flow onto the cast. You don't want to melt the cast iron, just get it red enough so that the brass and flux melts into it and coats it.

After you have made sure the cast iron has taken the brazing material, you can start building up the brass in the deep 'V'. Do the procedure alternating top and bottom.

After it is somewhat cool, use the die grinder again and 'V' out the MIG welds and the area around them. Repeat the process above to build them up. The key to the repair is to make sure the clean cast iron base accepts the first wash of brass/flux. This is the foundation for the built up brass which will give the repair strength.

You must have built up material wherever you can for strength. Brass isn't terribly strong, so your repair must have mass.

In summation, I will recommend you NOT use any stick (arc) rod for this repair. Melting the base metal complicates the metallurgy and will probably make the repair fail. You are trying to glue a little tab back onto a large hunk, then turn around and stick a bolt through that little tab and cinch it down.

This is a common repair. Expect to have to drill the hole true again, and if it's tapped, you will have to do that.

This is how I would do it...this is how I have done it. Others have had success using different methods...maybe! Good luck.

Stuart

I (well my welder anyways) has been successful stick welding cast iron exhaust manifolds. Here is the rod he uses:

http://www.alruqee.net/ind_mkt/RIM-CD&WEB/welding_consumable-files/utp/265-85fn.pdf

Other than the rod to my knowledge the secret is:

1. Only light preheat to take the sweat away.
2. Run short beads to keep the heat down.
3. Aggressively peen the weld and surrounding area after each pass with a blunt air hammer.
4. Get it in the sand, kitty litter, or asbestos blanket right away as grinding will generate “wind” that can induce cracking and leave it there for several hours to slow cool.

This process has worked repeatedly and passes MPI every time for me. I have no experience with brazing these however Stuart knows his stuff and I’m sure his suggestion will work as well. I also would not try to weld the tab back on but build a new one with the rod and a flat pc.of copper against the flange surface would give a good surface to build upon.

Good luck,

Curt B

If you dont care how it looks there is a clamp available for that type thing. I believe its called Clamp-a-stud. I know it's awkward but would work to get by.

Just weld the stud to the manifold with a nickel arc welding rod and grind until it looks good,
Scott

Outstanding tips all. It seems to be the cooling process that then causes cast iron to crack. If I understand the Curt correctly, bury the part quickly in sand to retard the cooling process?

Orchidskip,

Only if you melt the parent metal! When you melt the parent metal, the carbon molecules all rush to the molten site. If its cooled quickly, the carbon all remains there, and carbon is brittle...CRACK!!

If the weld zone is cooled very slowly, the carbon atoms have time to migrate back into solution, where they were in the recipie originally and you are off the hook!

Curt's method and filler rod is great for welding large castings like his split manifolds. Thick flanges and relatively thick cast manifolds with great fit-up!

If you used a stick rod on your little broken ear, especially without previous experience, the ear would probably go up in smoke before you could say 'jack sprat'.

Little funky repairs like that are the perfect place for brazing...in my estimation.

Stuart

brazing cast is on my "to improve" list for the year. i have had mixed results with the nickel rod. i have had it go in so good you had to hunt to see it. i have had it crack right beside the weld several times. want to really get down and practice my brazing on cast so it's good. either way preheat and slow cooling are pretty important. good luck

I also have welded cast with Ni5 Ny-Rod. We start out by preheating the cast iron then lay in a bead of Ny-rod then peaning then I do just a little different by warming the welded piece up along with the preheated metal then bury it in sand up to 24 hrs. depending on how big the welded piece is with a minuminum of 4 hrs. on a small parts. This releives the stress on the metal. This is a very good way to weld up expensive vices that guys break doing stupid things with cheater bars. The trick is Slow Cooling of the Cast. Once the cast is cool you can grind it down and sand blast the part to look like the org.
62Blue
Don

I have both welded cast with nickel rod and also brazed it, and have also had mixed results. Like others have already said, preheating and slow cooling is a very important part of the process.

IMHO: If it is a very rare, or difficult part to replace, I would take it to someone that specializes in that type of welding.

John

In the past I experimented with welding cast and when it cracked I vowed never to do it again. I'm glad I checked with you guys. I'll give it a shot. Thanks again, Don