Welding a broken cast iron manifold

[Jonny69]

Somehow I managed to shear the end off my exhaust manifold where the pipe attaches on the way to the NSRA Supernats. Irritatingly I threw my spare one away thinking I'd never need it so I upgraded to a tuned tubular jobbie, only now I'm "untuning" the engine so it lives a bit longer and I want to go back to the stock inlet and exhaust. I could either look for another manifold for a pittance or try and fix my broken one. I like fixing things and I'm a tight fisted miser so lets get on with it...

These are the two bits that need sticking back together:





I've cleaned them up as best I could and ground a shamfer on the edges so the weld has somewhere to go:



Cast iron is brittle and welding a cold manifold will probably crack it so I'm going to preheat it and weld it hot. She's out in case anyone is wondering. I wouldn't normally get away with this:



Gas mark 7 for 30 minutes, that's 220 degrees in new money. 'Scuse the state of the oven, I know I really should clean it...



While the manifold was in the oven I had a quick practice laying down some short beads on some scrap thick steel. Welder up on full:



When it came to the real thing I was expecting to use full power but the iron on the manifold is very poor and was just blowing away. I knocked the power back a notch to get a few weak tacks in place then basically worked my way round using the tacks as a starting point to melt in a small pool to fuse the two parts together. There was no way a continuous weld was going to work so it's not pretty but it's fixed:



In hindsight I think next time I have to repair something like this I'll gas weld it because it'll give me more control over what melts where and it'll result in a much neater join with better penetration. The amount of muck in the iron wasn't helping at all and made a lot of mess with the MIG.