27 Cast Iron Exhaust Manifold Brazing Demonstration:
Resurrection Autobody and Paint in Olympia, WA, contacted Muggy Weld with a cast iron 1963 Cadillac DeVille exhaust manifold in need of repair. Originally, the cast iron manifold was merely cracked, but the crack quickly turned into a hole as they attempted to make the repair.
Muggy Weld utilized SSF-6 Silver Solder and a MAPP gas torch (later replaced by an oxyacetylene when the MAPP gas ran out) to braze the cast iron manifold.
First, bevel the crack and clean the cast iron until it is shiny, then preheat the base metal to remove any moisture from the cast iron. This action provides for better bonding of the filler rod, and allows for more even cooling across the cast iron exhaust manifold. Once the cast iron begins to turn dull red, apply the SSF-6 flux and rod to the crack. Each time you deposit more SSF-6, be sure to flow it flat into the base metal before applying more rod.
If you run into an area in which the silver solder is not sticking, stop and re-clean the area to ensure no grinder residue is impeding the bond.
Old cast iron can be brittle, and while grinding the backside of the crack, a chunk of cast iron fell out. Fortunately, SSF-6 easily bonds mild steel to cast iron, so the hole was repaired with only 1/2 stick of SSF-6, and the cast iron exhaust manifold was ready to reinstall within minutes.
We covered the work area to keep the heat in and wind off while cooling (to eliminate cracking). After the part completely cooled, we used a sanding disc to remove the residual flux, but hot water and a wire brush or a wire wheel are just as effective.
Thanks, Resurrection Autobody and Paint!