Cold-formed flat top plunger for use in a hydraulic lash adjuster and method of making same

A method of manufacturing a cold-formed flat top plunger using a cold-forming machine having a cutoff station and five forming stations, the method comprising the steps of:

• at the cutoff station, shearing a wire to a desired length to form a slug having first and second ends;
• at the first forming station, squaring the first and second ends of the slug and forming an indentation in the second end of the slug;
• at the second forming station, extruding the slug at its second end to form a first bore that is defined by a cylindrical wall having a first inner diameter and an end wall;
• at the third forming station, punching through the end wall of the slug to form a hole having a diameter smaller than a diameter of the first bore;
• at the fourth forming station, upsetting at least a portion of the cylindrical wall at the first end to form a counterbore and a shoulder that at least partially closes the first bore, the counterbore having a second inner diameter that is greater than the first inner diameter, wherein the shoulder defines a retainer receiving surface and a ball seat surface;
• and
• at the fifth forming station, coining the shoulder to form the shoulder to final dimensions and forming a channel in a flat surface, on the end wall, the channel and flat surface formed to final dimensions.