GT Technologies assembles rocker arms with hydraulic lash adjustors from parts received from many different suppliers. A hydraulic lash adjuster is a device used for maintaining zero valve clearance in an internal combustion throughout its cold and normal operating temperatures. It compensates for the thermal expansion of intake and exhaust valves by placing a small hydraulic plunger between the rocker arm and the base of the valve stem. This system allows an internal combustion engine to operate smoothly during warm-up and normal operation and eliminates the need for periodic valve clearance adjustment.      The plunger operates off engine oil and the pressure created by engine operation. A ball bearing placed in a spherical seat inside the plunger acts as a valve for the oil. The plungers received from the supplier were once machined from pieces of bar stock and heat treated. The heat treatment would leave scale and other debris in the seat of the plungers. In order to ensure that the ball bearing valves would create a sufficient seal, GT Technologies would grind the seats with rotary grinding stone for a fixed amount of time. The supplier now uses a cold hardening treatment technique and the scale is no longer an issue, however, GT Technologies still grinds the plunger seats.