I am putting the finishing touches to an authentic, factory original type restoration of my 1952 GMC and trying to determine what the original correct finish on the exhaust manifold would have been. I have a similar question posted at the OldGMC site but have not received a satisfactory answer yet, so will try here too.
I have recently sandblasted a manifold from a 1952 truck that was in exceptional condition with no rust or pitting. Under the dirt and grease I found what appears to be a black porcelain coating that the sandblast would not remove. Interestingly on two other GMC manifolds I cleaned up I found traces of this same finish. On the one I just finished cleaning up, the finish is almost intact. Before finding this I was getting ready to apply the Caylx manifold paste to give it a natural cast iron finish, but now I am thinking that possibly in 1952 GMC was applying a porcelain finish to their exhaust manifolds. Here are a couple of pictures to give you an idea of what I am talking about.
picture1 picture2 picture3 It almost appears that the finish was applied and then the machine work was done to the flats where it mounts to the engine block and bosses where the manifold is bolted. I am speculating that originally in the manufacturing process GMC would have assembled the intake and exhaust manifolds to the block and then the entire assembly would have been painted with the engine paint eventually burned off the exhaust manifold revealing the black finish underneath. Does anyone have any insight about this?
