A power unit includes a rectangular frame base having a left shoe and a right shoe having a longitudinal track on their inner sides, a forward end having a support plate for receiving a jack stand, and a rearward end having a rear plate with an aperture for receiving an actuator shaft. After a rigid inner mold is inserted into the body, suction is stopped and the body is transferred to the outer peripheral surface of the inner mold. A heat exchanger is located in thermal communication with the plurality of cooling channels to transfer thermal energy from the airflow to the liquid coolant. When the Euler angle is set at, it is possible to reduce differences in each propagation direction by setting each propagation angle so as to satisfy a formula: \u03c8=0. Moreover, protruding pieces corresponding to the grooves of the upper cover are located on the lower cover forming a solid structural configuration.