Abstract: A container-filling machine having a continuously rotating member with an orbiting drive cam thereon which causes reciprocatory piston movement of the piston filler. An adjustment shaft carried by and radially of the rotating member adjusts the radius of the drive cam orbit, and the length of the piston stroke, when the adjustment shaft is rotated about its axis. A toothed rack is movable into the path of a pinion gear fixed to the end of the adjustment shaft so that interengagement of the rack and gear causes adjustment of the radius of the drive cam orbit as the cam moves in such orbit.