A mechanism is disclosed for actuating the intake and exhaust valves of a reciprocating multiple cylinder external combustion vapor expansion engine in either forward and reverse rotation. Electrical solenoid and pressure actuating valve mechanisms responding to a sophisticated digital computer program replaces the cam shafts, push rods, adjustable tappets, throttle, fuel injection, and cooling systems of a conventional internal combustion Diesel engine. The computer integrates the many system variables, including, temperature, pressure, speed, friction, mass, and acceleration to obtain the optimum efficiency of shaft work output.