SW Fuel Pumps
 

Does anyone know exactly what kind of plating was originally used to finish the pump bodies??

Gold anodizing??

I think it was a dichromate plating but not sure.....

Cad plating

Bill

I was thinking that but weren't the pump bodies aluminum or zinc? I thought cad is only used on steel?

Correct except it is not a plating but a chemical conversion coating. The reagents used to create it react with the base metal zinc and become chemically part of it. It is similar to the conversion coatings on many parts and assemblies including the bodies of some carburetors. The zinc castings of Holley® brand 4150/4160 carburetors were/have been treated to a zinc dichromate conversion process for decades. You can do the conversion coating process on parts made of zinc or plated in zinc. Cadmium plated parts are also typically given a dichromate conversion treatment to prolong corrosion resistance.

There are several variations of this family of corrosion inhibiting processes. The final color can be quite variable shades of yellow, gold, green, and even black. Sometimes color coding dyes are applied over the parts in addition to the conversion coatings. As purely a corrosion inhibitor the exact color is probably not important to any O.E.M. as it is the corrosion resistance they were/are after. Done well the parts can be protected from high humidity and or salt sufficiently to ward off warrantee claims. Bare zinc corrodes very aggressively and quickly (in minutes) in the ASTM salt fog testing for new parts. Well done dichromating can give parts fairly good protection for days of direct warm exposure. The final appearance and color achieved is a combination of several processing variables so there will be a lot of batch to batch variability.

Dan

Well done, engineering perspective with chemistry.