Abstract: A method of assembling a downhole well pump system comprising a reciprocating piston pump having a total vertical length exceeding the clearance available in most factories. The pump comprises a tubular body which is positioned horizontally within which an upper barrel section is threadably secured at the end corresponding to the top of the barrel section when the pump is in a vertical position. The lower end of the barrel section thus rests on the lower interior surface portion of the shell. A pair of axially spaced pistons are mounted on opposite ends of a piston tube and the piston tube slidably traverses a divider which has threads for connecting to the bottom end of the tubular shell and a cylindrical surface for snug insertion into the bottom end of the tubular barrel section.