To provide an energy-saving cam drive exhaust valve operating system capable of flexibly controlling the switching timing of an exhaust valve of a cross head type large-sized two-cycle diesel engine.

The actuator system comprises a plurality of cylinders each having at least one exhaust valve 11, at least one cam shaft 28 each having an exhaust cam 29 for operating at least one exhaust valve for each of the cylinders, a hydraulic actuator 34 provided for each exhaust valve 11 for moving the exhaust valve 11 to the opening direction, and a hydraulic piston pump 32 provided for each hydraulic actuator 34 so as to be driven by the corresponding cam 29 on the cam shaft 28, and controls so as to add pressuring actuator oil to a hydraulic push rod for opening the exhaust valve by timing earlier than that determined by the exhaust cam shape or opening the same by an amount larger than that determined by the exhaust cam shape.

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