Four-stroke internal combustion engine with valve resting mechanism

Object: To provide a high performance four-stroke internal combustion engine wherein increase in side of a cylinder head is prevented and a valve resting mechanism is provided for a valve lifter. Solving Means : In a four-stroke internal combustion engine (1) with a valve resting mechanism wherein a valve lifter (18a) having a valve resting mechanism is interposed between a valve motion cam (22a) and a stem (16a) of a poppet valve (14a) and a valve lifter spring (38 or 39) is provided for biasing the valve lifter (18a) in a direction in which the valve lifter (18a) is normally held in contact with the valve motion cam (22a), a slide pin holder(43)which is pressed against the valve lifter (18a) by sprint force of the valve lifter spring(38 or 39)is provided on the valve lifter (18a) while a shim portion(27)having a different thickness for controlling a relative positional relationship with the valve lifter (18a) is formed integrally with a valve lifter top wall(40a), and one of a plurality of different valve lifters (18a) which is most suitable for the relative positional relationship between the slide pin holder (43) and the valve lifter (18a) is selectively mounted to effect tappet gap adjust.