A method of assembling a pump motor and preloading bearings of the motor including providing a housing, an end bell, first and second bearings each having a plurality of rolling elements disposed between an inner race and an outer race, a rotor assembly having a shaft, and a spring, securing the outer races to the housing and end bell, respectively, assembling the spring on the shaft, inserting the rotor assembly into the housing such that the spring bears against the inner race of the first bearing and the rotor assembly, attaching the end bell to the housing, and securing the inner race of each of the first and second bearings to the shaft.