Pot Metal Goes to Pot

You can curse almost any owner of an old car by muttering the phrase "pot metal." An alloy of (typically) zinc, tin, copper, lead and other base metals, pot metal was widely used for castings in Super Six Hudsons. Pot metal melts at about 900° F. -- about half the 1800° of brass and bronze. It's called "pot metal" because it would melt in an iron pot.) Because of the low melting temperature, low shrinkage as it cooled, and the low cost of the component metals, pot metal was widely used in the auto industry through the '20s (and beyond) for door handles, window cranks, other interior and exterior hardware fittings, and some "structural" components. However, pot metal is weak and vulnerable to breakage. Over time, micro-grandularities in the metal oxidize. The oxides expand with moisture, further wedging and enlarging cracks. Impurities in the cast metal can accelerate the process. Almost without exception in Super Six Hudsons, some pot metal fixtures have become broken by the time the car has wended its way through seven-plus decades.

The list of pot-metal components of the 1929 Hudson Super Six is long, and sad. Owners of these old cars have developed an impressive network of foundry and machine shop resources to replace broken pot metal items with brass and bronze re-castings. The catalog of pot metal items includes:

• Carburetor float bowl. This page discusses the problem in detail and discusses alternatives to the highly vulnerable pot metal float bowl in the Marvel carburetor. Pot metal is especially poor as a carburetor material because gasoline attacks and crystallizes the lead in the amalgam. The photo at right shows where part of our carburetor broke off. An old crack, darkened by oxidation, shows on the right-hand side of the smaller set of threads, where the fuel line came into the carburetor. This was on the rear of the float bowl. The crack dumped raw gas into the engine compartment whenever the fuel pump was turned on.
• Front seat mechanism on Briggs-built Hudsons. Briggs used a pot metal casting as the "nut" for a screw that moves the front seat forward and back. I have found a machine shop that made me (and other Briggs-body owners) a replacement.
• Steering wheel bracket. It's OK on our Town Sedan, but other Super Six owners have been forced to cobble together alternatives.
• Cowl vent arm. Super Six Hudsons have a "cowl vent" just in front of the windshield. When the hinges get a little rusty over the years, someone applies extra force to the arm, under the dashboard, that operates the vent. Boom! Another broken pot metal casting.
• Exterior door handles.
• Interior door handles, window cranks, door pulls, etc.
• Rear seat foot rest brackets.
• Radiator caps.

An excellent source for well-made replacements of is Geoff Clark of Palmerston, North Island, New Zealand, who has a local foundry that does excellent work casting replacement hardware parts in a bronze alloy. You have to get the plating done yourself after you get these parts from Geoff. But the quality is very good, thanks to Geoff's vigilance with the foundry, and the prices are very reasonable, due in part to favorable US-NZ exchange rate. Among the parts Geoff has made or is in the process of making: Pine Cone pattern and Rose pattern interior and exterior door handles, interior door pulls and window cranks; Rose Pattern foot rest bracket; cowl vent arm; and radiator caps (including a nice Rose Pattern cap that looks like it should have been OEM, but isn't.) e-mail him directly for anything you need in the way of cast parts. He's also a great resource for old Hudson and Essex parts generally, and he's a great source of information about old Hudsons.

Before we're through restoring our Town Sedan, we're likely to have considerably enhanced New Zealand's trade balance; our list of broken pot metal items includes an exterior door handle, the cowl vent arm, a foot rest bracket, and the carburetor float bowl. (Geoff, by the way, rescued me initially from the broken float bowl by providing a pot metal replacement. Without him, I still wouldn't have the car running. Thanks, Geoff!)