Intergranular Corrosion (IGC) in the zinc die casting alloy.
Early zinc die castings, i.e., in the 20's-30's had so many
problems that many of the castings made back then will literally
crumble in your hands today. Zinc castings were often made from
recycled alloys and poor control over what went into the
melting pot created problems in many products.
Aluminum die castings are much more stable over time than
zinc castings.
One of the major problems with the 'B' was the fact that the air
horn used only 4 screws to hold it down to the main body. Had
they used a few extra fasteners it would have helped stabilize
the die casting and many of those badly warped early 'B's would
still be usable today. Adjustments to the alloy in later
Rochester 'B' versions is the reason they faired better than
the ones made in the early 50's.
Lots of information on the web pertaining to the IGC problem.
Denny Graham
Sandwich, IL
Last edited by Denny Graham; 01/06/2014 12:16 PM.
