lightening the crank has little effect because the mass you can remove is so close to the center line. You can shape the crank lumps to a wedge shape to reduce drag (oil/air mist) and polish the crank, but you would not notice any real life application difference at the speeds you would be spinning it. Lightening a flywheel from the outer rim is very effective because the weight is so far from the center line. Reciprocating masses matter too, lighter pistons and rods help.
