Abstract: Employee #1 and an assistant were removing the lower end of an oil well pump unit pitman arm to change a worn pin. A gin pole track was used to rotate the unit's counterweights to an elevated position; the counterweights remained connected. A chain and load binder were placed between the front of the unit's walking beam and base to counteract the counterweight's energy. A hammer was used to drive the arm off the pin. It was nearly off when Employee #1 moved the chain and binder to the tail of the beam. The assistant, standing in the unit's base, applied the binder. Employee #1 then leaned over the base under a counterweight and helped reapply the binder. As the binder went home, the counterweight, held by the track line, overcame its friction mounting and slipped, breaking the chain holding it. As the counterweights rotated, Employee #1 fell across the base. The counterweight he was under struck him across his shoulder and then severed his head; the assistant was not injured. The initial position of the chain and binder counteracted the counterweight's energy; their movement to the rear of the beam increased the energy being held by the track line. No other energy restraining device(s) were used to counter the combined energy potential of the counterweights and binder.