proper way to weld cast iron

[TBART70]

what is the proper way to weld cast iron engine block,
I have ni-rod and a torch, how hot should the base metal be !

[Matt@RFR]

Do your weld prep with a cutting tool (end mill, carbide rotory cutter, etc.) NOT a grinding tool. Then pre-heat the entire area to 300ºF. Use the Ni rod you have at an otherwise appropriate amp setting for steel. Some will tell you to use only 1/2" long welds or so, but with the pre-heat that becomes pointless. Just make sure there are no temperature spikes at any time.

For cooling, you have two choices. 1) Peen the weld itself and the HAZ until it's cooled to below 300º, or 2) using fire blanket, a hole in the ground filled with sand, a big oven or with your torch, alloy the whole deal to cool very very slowly. The slower the better.

A combination of the above two is prefered but not necessary.

One tip: Don't over constrain the two peices. That's a sure fire way to get the thing to crack as it's cooling. It's going to move alittle, and you have to let it.

[TBART70]

Thanks Matt, it is a crack about 1" long, I drilled the ends of it and v-ed it out a little. how far around should it be heated, right at the weld spot or uniformally around it, I would think a broader area would be better for slower cooling. Thanks again!