Cracked exhaust manifold

perfacar said
hi, the area has to be clean. welding with stick is the best way. use a machinable nickel rod. or there is cast rod now. v out the crack, weld bout one inch, stop, remove slag with a slag hammer, keep hitting on area with slag hammer for bout a minute. when you can touch it without burning finger, then weld another section, repeat with slag hammer. when you pound with a sharp end of a slag hammer, it stress relieves the cast iron. do not heat it before, cast is not a very stable metal when hot. weld at room temputure.
I 've welded cast this method. exh and blocks, heads. from a pipefitter/welder.

I got the nickel rods the other day and practiced on a cast iron brake rotor that I smashed in half. I welded at room temperature, and stress relieved with the hammer afterward. When all was done, I went back to the street and threw the rotor in the air trying to break the weld. After 6 drops, the rotor finally broke, but not at the weld! The weld was stronger than the castiron. Thanks for all your advice.