Does anyone know what material the early chrysler 331, 354, 392 hemi cranks were made from? I know they are forged, but are they 5140 steel? Im getting one nitrided and they wont heat treat it until they know the exact material. I had never stopped to think about the material, just that they were forged.
The winner is 1050 alloy. Finally got someone who knew. Even Gene Adams didnt know. Marine Crankshafts in California was able to confirm that early chrysler hemi cranks are 1050.
I didnt even realize any of the stock chrysler cranks came from the factory nitrided for the gen 1 motors. Im doing it because its a race car and I cracked one last season, and Im hoping this makes it last a little longer. It was very affordable. Even if I had to grind it -.010 and have it nitrided again. Its only $125 to have it nitrided.
I had Henry at Velasco do two cranks for me. Both offset ground to BBC journal size and he nitrided both. Also tapped the flywheel bolt holes. Mile high cranks in Colo is good also. Lippy
Old HAMB metallurgist here. Just providing some info on nitriding, it is only about 0.001 inch thickness. Very thin, but does significantly improve surface hardness. That is why if you get the crank ground at all, the nitriding that may have been present is long gone. Nitriding is done at approx 1000F temps, low enough the crank will not be distorted after the process. It also produces slight residual compressive stresses on the surface, which are beneficial for fatigue crack resistance. Carburizing is another way of surface hardening, but done at higher temps and can be 0.010-0.030 depths. Because of the high temps required, like red hot range, it is not an option due to distortion that can result.
They wanted to know what the alloy is because the temperature they heat is to during the process of nitride hardening depends on it. I know all the flathead 6 cranks in the Canadian 25 1/2" motors were 1050 alloy and of course forged right from day 1 when the engine plant opened in 1935 for the 1936 model year. Were spinning out early 50s flathead six mopar well close to 7500 rpm so even a heavy polish can damage the hardening. Definitely if you turn the crank at all you would want to nitride it if you want it back to what came from the factory with, obviously even more important if you intend to stress it.. lol
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