Method of assembling a pump motor with bearing preload

A method of assembling a non-reciprocating motor adapted for driving a reciprocating load, the method comprising:

• selecting a housing having first and second ends and a predetermined coefficient of thermal expansion;
• selecting a first bearing having a plurality of rolling elements disposed between first inner and outer races and having a predetermined coefficient of thermal expansion that corresponds to the coefficient of thermal expansion of the housing;
• selecting a second bearing having a plurality of rolling elements disposed between second inner and outer races and having a predetermined coefficient of thermal expansion that corresponds to the coefficient of thermal expansion of the housing and to the coefficient of thermal expansion of the first bearing;
• selecting a rotor assembly including a longitudinally-extending shaft and having a predetermined coefficient of thermal expansion that corresponds to the coefficient of thermal expansion of the housing, to the coefficient of thermal expansion of the first bearing, and to the coefficient of thermal expansion of the second bearing;
• positioning the first bearing in the housing;
• positioning the second bearing in the housing;
• rotatably mounting the rotor assembly in the housing with the shaft received in the first and second bearings, such that the rotor assembly is in a first position having a predetermined amount of axial and radial play relative to the housing;
• installing a biasing element between one of the rotor assembly or the housing and one of the bearings, such that the biasing element forces the rotor assembly to a second position in which the axial and radial play is eliminated;
• and
• permanently securing each of the first inner and outer races and the second inner and outer races to one of the rotor assembly or to the housing, such that the rotor assembly is retained in the second position over a temperature range of about minus 40 degrees to about 105 degrees Celsius.