The final component that we will examine is the heart of the diesel injection pump; the rotor. (Figure 4-77). Due to the extremely close tolerances of the rotor and head assemblies, a thermal relief groove has been incorporated into the rotor design. Thermal shock can cause a head assembly to contract, resulting in the seizure of the head and rotor. To lessen the possibility of this happening, a reduction in the rotor diameter at the area between the ports has been added.
The rotor in 1980 through 1984 pumps incorporates residual pressure balancing ports. These small vent ports operate by simultaneously registering with the head discharge outlets shortly after each injection. This operation allows a balance of the residual pressures between injection lines and helps smooth out the operation and the sound of the engine.