A valve operating mechanism is provided with rocker shafts, cam followers press-fitted to one end of the rocker shafts respectively, and rocker arms press-fitted to the other end of the rocker shafts respectively. Approximal surfaces are formed in the cam followers and the rocker arms respectively, and reference planes are formed in a engine body, which come in mutual contact with the approximal surfaces in their rotational direction when the relative phase angle of the cam followers and the rocker arms is proper with each other. Thereby, the invention enables fixing of the cam followers and the rocker arms to the rocker shafts at a proper phase angle and checking if their relative phase angle is proper. |