Whenever you change masses on your rotating assembly, you need to have it balanced.
This means if you change your rotors, machine your rotors or change counterweights. The RPM of the assembly when tested is important due to it's resonant frequency. At one particular RPM things might look as smooth as silk, but only go 20RPM above that and things can start shaking violently on an unbalanced rotating assembly. That is something that would then be taking out on your engine's bearings, shortening their life, and also on the seat of your pants. Not very nice to experience when you think you are running something that is supposed to be smooth, as rotary engines are supposed to be.
Our purpose built balancing rig has been designed and built in-house specifically analyse vibrations in your rotating assembly at the correct RPM, and make the appropriate mass alterations to have it spinning like a gyroscope!