Hi Matt:
If memory serves me correctly, the reason that the crankshafts were heat
treated is to essentially harden them. The later, I think 1968 and on,
crankshafts were made through a casting process, thus requiring heat
treatment and subsequent machining. The early crankshafts were
manufactured by machining forgings, requiring less stress relief and
hardening. The reason for the move to the casting process was cost and
the ability to rapidly ramp up to meet MGB and other variants of the B
series engine rate production. So if you find any early five main
cranks, keep them. Lindsay Porter published a book called "BMC and
Leyland B-series Engine Data" it provides a historical account of the
B-series engine, its applications, and technical data.
Good Luck: Rich Boris
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