Yeah and files snap like twigs when you put any kind of load on them as well, not exactly what u want for a crank. U can take 4140/4340 to the low mid 40's for RC with full heat treating but that's where u want it for making vice jaws, tooling (not cutting tools), and for something thay needs high wear resistance. The higher u go for RC, you lose toughness and maleability, which a crank needs. Go to most any machine shop and ask for a shaft/ bushing whatever to be made and it needs to put up with alot of abuse (loader bucket pins/bushings etc) and they go right to there rack of 4340 and use that in its non heat treated form, which is in the mid 20's for RC.
With all the torsional/longditudal forces on a crank I don't think u would want it very hard, although my experience is from the general maching end of it so I could be wrong
I used the file as a reference point so he could
get a idea... thats all... if you want the right numbers
its wise to call the manufacturer of the better
cranks and rods... on the axles I pulled the prints
at work(Chrylser) so I could get the RC range so
I could get a set of axles cut and hardened to the
upper end of the spec
