cast iron exhaust manifold with a ~4" long hairline crack. if it weren't for the smoke, the crack would've been difficult to spot.
wanted to weld the cast iron with the tig welder. thought i could fuse the crack without filler. first pass, closed the crack. just to be certain, i ran a second pass with SS filler (308L)
now i know SS isn't the right filler for cast, but.. i recall hearing somewhere that SS filler could join cast iron to mild steel. maybe i misheard.
after laying down a beautiful bead, we reinstalled the manifold and fired the engine up. 10 minutes at idle and the bead split right down the center. its like the original crack floated to the surface. i couldn't draw a line down the bead that accurately!
did it crack because of incompatible (stainless) filler? if yes, why didnt it crack along side the bead? i'd think the weak spot'd be the interface between the stainless and the cast iron.
i pre- and post-heated the manifold. drilled out both ends of the crack. let it cool down for over an hour in a draftless shop (lunch time).
-tony