When the pump is operating, the force required to displace the plungers inward plus the momentum of the rotor assembly transmitted by the rollers, produces the cam loading force. This tends to turn the cam in the direction of rotor rotation. (Figure 4-59). This movement retards the pumpโs timing.
This cam loading plus spring force is transmitted to and opposes the power side forces. The combination of forces positions the advance mechanism at a definite point for each full load speed. At part load the reactive forces diminish and are not as effective in opposing power side forces. As a result the cam assumes a more advanced position.
