Yes, Benny, forged cranks have parting, or forging lines. These lines are ground down after the crank is stamped, which leaves the distinct look of grind marks, as opposed to the non-ground casting mold parting line.
Also, the surface of the cast crank is different from that of a forged crank, in that it is more like an orange peel, whereas the forging is slightly smoother.
Forged cranks were the norm in older bikes and older Detroit cars, especially HP engines, since they were almost always stronger.
But, Pontiac used cast
steel cranks for some years, and Ford used
nodular iron cast cranks in many HP motors, and both of these are really tough items.
Aftermarket crank makers (like Crower) have made cranks out of large steel billets. (I've seen Crower's crank milling machine in action and it's impressive how it roughs out the basic unit.)
Remember that forged cranks used to be made in a couple of forging stampings: first a flat mode, and then a twisting of 90* on each end of a V-8 crank, while the center section was held fixed. These twisted forgings were not at optimum strength where the twisting was done, BUT, later, advanced techniques were developed to where the manufacturer could do a NON-twisted forged V-8 crank, where the metal grain was not stressed.
Many bike cranks have been built-up ones, made of several pieces pressed together, in both single and multi-cylinder versions. This is easier for an engine manufacturer to build, as they don't need a dedicated crank grinding machine.
There's lots more to be said about car and bike cranks (and radial aircraft engines with a master con rod and slave rods), but that would be hijacking this great thread even worse. Anyone interested in really neat bike cranks can go here to learn more:
http://www.faliconcranks.com/
