[hawk]

Something I wrote in another thread:

The harmonic damper is there to absorb torsional vibrations of the crank, principally at harmonics of the rotational frequency. The crank is not rigid, it twists and rebounds like a very stiff spring in response to the power pulses coming from the individual cylinders and associated pistons.

The crank in conjunction with the harmonic damper forms a classic "spring-mass-damper" system. The response of such a system is sensitive to the spring rate, the effective mass, and the characteristics of the damper. In the case of a rotational system, the absolute mass is not as important as the rotational effective mass which is a combination of the static mass and the mass moment of inertia (MMOI - essentially a measure of the geometry of the system and how the mass is distributed).

Smaller pulleys, with a lower dynamic mass thanks to decreased MMOI, allow excessive torsional vibrations, and those are what damages the relatively brittle gerotors in the pump.

Or at least that is my understanding...