Mig welding a cast iron manifold

I would like some information on welding a cast iron manifold on a boat. There is a 1 inch long crack, on the Y pipe of a mercruiser and is a cast
iron metal. I would assuming drilling a small hole at each end and placing a small V in the crack, I could weld mig weld the crack, and peen it afterward. Is this the correct method, and how well will this hold up. The material is only about 1/8" to 3/16" thick. If peening the material afterward, I would assume I will not be able to hit it very hard. I am hoping to weld this, as the part is not very expensive to replace, just alot of work involved in removing it. I am able to weld the brocken piece without any problem.
Thanks for any help in advance.
Cheers,
Dale
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You have nickel MIG wire? This is a job for cold welding with nickle. Peening is not a matter of hitting it hard - it's a matter of hitting it a lot, quickly, to help the nickle stretch with the cast iron as it cools.
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So, would there be a better rod for use in a stick welder instead of mig welding, or I will have to check with my local supplier for some nickel mig wire? Is this common?
Thanks,
Dale
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Since I have not yet ponied up for a wirefeeder or even a Readywelder, I don't know about availability of nickle MIG wire - I expect it can be gotten, though if the price of nickle stick electrodes are any guide, the price may be a bit shocking. I use stick, and I was trained to repair cast iron using 99% Ni rod with a stick. A 1" crack should be a 1 stick (or 1/3 stick) repair.
Not that you couldn't try it with regular steel MIG, but from what I was taught that's not likely to make a repair that will stay put. Considering that it was some years ago that I was in class, there might be newer methods that some other folks here know about better than I do, so stay tuned for more information.
Much past discussion here indicates that exhaust manifolds are more of a bitch to repair than heavier hunks of cast iron. MIG brazing (discussion here definitely indicates that that wire exists) may be an easier repair for a one-off.
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