Message for John (UK)

Welding cast iron is tricky. It is tricky for the welder himself, and it is tricky for the company which make the welding rod. The reason for this is that cast iron expand so much when heated.
I have never heard it was possible to weld cast iron with a mig welder, but then, I have heard so little of what is to be heard in life, that it may be possible too.

In general, there is 3 ways of welding cast iron, weld it cold, weld it warm, and weld as it was regular construction steel.

To weld cold, you normally use a nickel rod like UTP 8, and weld just a small bit, so small that you can put your hand directly on the welded spot without getting burned. Yes, it is possible. When welding just a short distance, in the time you have removed your mask, and taken off your gloves, the weld should be cool enough to touch. Then, use a pin hammer to hammer the weld out. Weld a little more, and hammer it. If the cast iron gets too warm, you need to slow down and let it cool until it has a low temperature before you continue.

Second way is to weld hot, it means you have to warm the entire piece of cast iron, and then you can weld, more or less as regular construction steel.

Third way is to neither weld cold or hot, but just weld. To do this you need a special welding rod, and I have no idea if anyone else than Certanium makes such rods. You just weld as if it was regular construction steel, and it sticks, and it will not break or crack....
I have seen engine blocks repaired like this, only the coolant emptied so much that it was not sipping out of the crack... then the crack was welded, from one end to the other... it was allowed to cool, then coolant was topped up, and the engine started and the boat left for the fishing fields.

As John says, it is a good thing to drill a hole at the end of the crack to stop further cracking, and then grind a V to fill up.

I have used the Certanium welding rod myself, I have some. But, I have used it a very little so I am not very used to it, as I got it very recently.
The way I am used to, is the cold welding method.

Best regards, Bill

I've welded steel for years and cast occasionally for a couple of years, an engine block is probably not the place to learn how to weld not to mention welding cast. If you are new to welding this would be a good time to hire it done. I don't know about the continental motors but the Ford N blocks get welded somewhat frequently and successfully, depending on where the crack is. If the crack is internal in the block there are comapnaies tha can do it but that is another story.
just my $.02