You can take off a lot of mass by rounding and smoothing the CW's and cleaning up flash and sharp edges from the original forging. BUT, it won't be nearly as effective at removing bobweight as lathe turning, because you're working at a closer radius to the crank centerline. It's just like torque, force times distance. An equal force/mass at twice the distance from center is twice as effective.
What I did with my factory crank projects is to go apeshit with the grinder first, then send it off to get the journals ground(if needed), nitrided and then do final balance, lathe turning etc etc. S/F....Ken M
