I have limited experience welding cast, but have done it. Had to repair an expensive racing engine block one time. It was a shot in the dark, either fix the old block or buy a new one and than do all the expensive machineing needed to get it race ready. Nothing to lose by trying to weld it so I did. First thing I did was drill the ends of the crack. Then vee'd out with angle grinder. Then took a propane torch (weed burner) and preheated around the weld area to 900*f. I kept the propane torch handy during the entire welding process. I would weld about 1 inch at a time using my mig and 70es wire. I would then take the torch and apply heat until the entire weld area was a even 900*f and then repeat procedure of welding, 1 inch at a time and add heat. Once weld was complete, we set the entire engine block over the wood heater with a roaring fire and let set until fire died and engine cooled off. No cracks and engine won ten races that year and has been rebuilt several times since.
I also brazed up a old water pump that had froze and busted the whole side out of it. I didnt have the money to buy a new pump, so it was either fix it or do without water. Followed pretty much same procedure as welding the engine block, except at that time I didnt have a propane torch to preheat with. Since it was winter and I had a fire in the old barrel stove, I set the pump head on top of the stove and did all brazing with pump setting on the stove. I had every thing on I could to keep the stove from burning me up while brazing and it took several step backs away from the stove for me to cool off before the braze was complete. Left pump head on stove over nite and put together and reinstalled the next day. Far as I know that pump is still in the pump house and working fine.
