Abstract: A self-aligning connection between a rotary and reciprocating pump piston allows relative radial movement between the pump piston and the rotary cam. The self-aligning connection is formed by a pin carried by the rotary cam and is positioned in a radial recess located in the pump piston. An improved drive for the rotary cam is perfected by a cam follower pin supported from the housing by a roller bearing race which is pressed fitted within a bore formed by the pump housing. The pump piston abuts a TEFLON pad located in the pump cylinder to reduce dead space and insure that the pump produces accurate volumes. The employment of different plastic materials between the rotary cam and the pump housing provides an improved bearing surface.