The Crank Pulley on the MINI Cooper engine not only functions as a Harmonic Balancer but just as important it drives the pulley for the Supercharger and alternator pulley. The job to connect all the pulleys together is accomplished with a Serpentine belt, also known as a Multi-v or Multi-Rib single continuous belt. As the crank pulley is the main drive pulley not only does it do most of the work load but the diameter of this pulley sets the speed of all the ancillaries. Changing the diameter of this pulley will also change the speed of the Supercharger (and thus the water pump) and the alternator.
The "other" function of the crank pulley is actually the more critical as the job of controlling vibration has turned into a very high tech exercise. The damper part of the pulley is composed of two parts; the first part is simply a mass that resists the acceleration of crankshaft vibration. The second part is the energy dissipating part that absorbs the vibrations. It is this part of the pulley where different engineers that different approaches, some will simply use a rubber element, other will use a centrifugal clutches and yet another will use a fluid element.
The Stock Crank Pulley as designed by BMW uses rubber as the element of vibration control. While this design is probably the oldest and most commonly used, production problems and sever demands from a modern engine has resulted in a number of series failures.
Fluid Damper Pulleys are made with an internal steel inertia pulley ring that is surrounded by a high viscosity silicone gel. The internal intertia ring "floats" in the silicone gel to combat the engine harmonics at all RPM ranges. Crankshaft and bearing life is significantly improved and safely increases torque and horsepower.