Cast iron is very tricky. It depends on the mass of the piece you are welding on. If it's relatively small Welco 65 in 3/32 or 1/8 inch is some pretty good welding rod and you don't usually have to preheat, and cool down slow like larger pieces. I believe this will work for what you're doing. However, for something like an engine head, you need to bring it up to about 500 degrees and keep it hot while you're welding it. I used Welco 95 on a Chevy racing engine "Bow Tie" head that had two holes the size of half dollars knocked out of the two middle cylinders between the valves. I cut 1/4 inch mild steel plugs that just fit flush in the holes. I positioned them and after pre heating I tacked them into place. You will get all kinds of trash from the oil that the cast iron has absorbed and your welds will have all kinds of pinholes from the trash vaporizing while you're welding. Regardless, I welded them up all the while keeping the head hot. Then I went back over the welds with a TIG and just puddled the weld together. You have to keep working the molten nickel until it fills in the hole and move on to the next one. Do that all the way around and when you're done cool down very slowly. Usually it takes about 24 hours to bring them back to ambient temperature. Believe it or not the guy I did it for was out winning races with that head the very next week.
Last edited by Mocopperhead; 04-28-2007 at 08:56 PM.
Reason: I needed to tell him what rod and the diameter to use in his case.
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