37lookin - you can arc weld cast iron with nickel rod and it works well. It is often used in large truck blocks to patch holes and cracks. Since big diesels are megabucks to replace.
But! and this is a big BUT!
If you have a crack. You must drill a small hole in each end then weld it. If you do not drill the hole at the end of the crack, when you heat the metal, the crack will expand and continue to grow. The weld is more of a brazing process than welding, so its not actually welding the metal but attaching the metal like soldering.
If you do not prepare the crack by counter drilling, you will have problems later.
In the instance given above, there is no crack to expand. So the nickel rod should hold well. But with a cracked block you need to stop the crack. The weld wont do that on its own and you will have problems later.
It is also recomemended that you only weld about a 1/2 inch at a time, peen the weld with a small hammer (lightly) for stress releif and then weld the next 1/2 inch untill you finish.
If done correctly, the weld should hold for many years.
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