The Stovebolt Site Forums The Shop Area Engine Shop Cracked exhaust manifold

The right side exhaust manifold on my 69 Pontiac 400 engine in my truck had a crack length wise across from the Siamese center exhaust port. It was cracked when I bought the truck two years ago. I had the manifold brazed and it held up till now. A few weeks ago on a 100deg+ day I got stuck in stop and go traffic for over 30 mins, the engine got hotter than I have ever seen before, probably 200 deg. The manifold cracked again and most of the brazing popped off. It seems these manifolds are like chicken teeth, but I finally found one, on ebay, from a '68 that did fit OK. Truck is up and running again, like new. My question is, I would like to have the cracked one repaired, and heard that welding with cast iron rod, after heating manifold in a oven is the best way to go?

Find somebody other than the person who "brazed" it. A good braze job (properly prepared and brazed) would not have failed. Find somebody who can weld, braze, or otherwise repair it properly. Cast iron welding is a real art, and few people can do it right. Preheat, weld with nickel-alloy rod, post-heat, and peen the weld thoroughly while it's cooling, then bury the part in a pile of sand overnight to S-L-O-W cool.
Jerry

Thanks, Jerry for the info, l'll see if I can find a qualified welder. No hurry, as replacement manifold seems good. Duane

Brass needs to be applied to a totally clean surface. I usually use an angle grinder and a cup brush to clean an area at least 1" wide all the way around the place I intend to braze, and get the metal hot enough to melt the brass rod by simply touching it to the red-hot workpiece. Use plenty of flux to assure a good bond to the base metal. The brass should flow smoothly over the surface it's being applied to and bond like solder does when it "tins" to an electrical connection. If the brass piles up on top of a repair, the base metal isn't hot enough. Once an initial bond is made, additional layers can be built up to strengthen the repair if desired.
Jerry