A uniformly preset spring force pre-load among a number of identical solenoid actuated valve assemblies (28) by uniquely adjusting the spring pocket length (L) of each respective plunger (12) to accommodate a respective spring (20) which is uniquely mated thereto. This adjustment is accomplished using a two-component plunger (12) consisting of a plunger body (14) having a central bore (22) and a rod (18) slidably located within the central bore. The rod (18) is press-fit into the central bore (22), and the spring pocket includes a portion of the central bore unoccupied by the rod. By pressing the rod (18) a selected distance into the central bore (22), a precisely set spring pocket is obtained which is uniquely correct for a selected spring (20), in that the selected spring is compressed to a precisely preset spring force pre-load. The adjusted plunger (12) and spring (20) are uniquely assigned to each other to collectively form a customized plunger assembly (10) having a preset spring force pre-load, whereupon a valve assembly (28) is manufacturable therewith having the precisely preset spring force pre-load. In carrying-out the adjustment of the plunger (12) with respect to a specific spring (20), the rod is pressed into the bore by a controllable source of force, such as for example provided by a stepper motor (88), and the spring force pre-load is monitored by a load cell (78) to ascertain when the desired spring force pre-load is achieved. Monitoring and force control is preferably automatic via a micro-controller (98), but may be manual.