Understanding Crankshaft journal hardness

[MikeK]

John, those cast aftermarket Model A cranks were cast nodular (spheroidal graphite) iron, not cast gray iron. They run extremely well at a lower hardness than a steel forging. In many ways cast nodular iron cranks are far superior to steel forgings. Nodular iron absorbs harmonics rather than ringing like a bell and is much more resistant to failure from stress-riser points than most heat-treated steel cranks. It cannot crack like cast gray iron or hardened steel, the microstructure is different. If they were available today I'd take one over a steel crank for an A.