Variable valve operating mechanism of four-stroke internal combustion engine

A variable valve operating mechanism of a four-stroke internal combustion engine, in which a valve lifter provided between a valve operating cam and a valve stem of a poppet valve is slidably supported by a lifter guide hole and always energized by a lifter spring in a direction to abut on the valve operating cam,

• a slide pin is fit to a slide pin holder attached in the valve lifter and freely slides in a direction orthogonal to the valve stem,
• a stem contact surface which abuts on the valve stem of the poppet valve energized by the valve spring and a stem through hole which the valve stem penetrates are formed in adjacent to each other in the slide pin, and
• the slide pin is energized by a pin spring in one direction while oil pressure acts on the slide pin in an opposite direction through an oil pressure supply passage, and the slide pin is moved by controlling the oil pressure to cause the stem contact surface and stem through hole to selectively face the valve stem,
• the variable valve operating mechanism comprising:
• an oil discharge passage including a discharge port which is opened to allow oil acting on the slide pin to be discharged when the valve lifter is pressed by the valve operating cam to move for opening the valve,
• wherein the slide pin holder includes an outer peripheral recessed groove for communicating with the oil pressure supply passage.