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
