Originally Posted by pitbull2332
You need a nickle rod to weld cast iron. To do it you need to preheat the block to 550 degres and cool it slow. I usually wrap it in a welding blanked and let it be. On the crack v it out good and drill an 1/8" hole at the end of the crack to stop it from spreading. I know this is not what you were looking for being an assembled motor, But it is the proper way to weld cast iron. also be aware, welding can arc between your bearings in the crank and pistons to cylinders ect.
so keep your ground as close as you can to the spot you're welding.
also, if it's just a water jacket you can use JB weld, buddy of mine had an old 79 blazer with cracked water jackets that someone just plastered JB weld all over the side of the block, it was compleatly fine until you started beating on it alot and it'd leak a little bit.