Abstract: A valve operating apparatus for driving intake valves and exhaust valves of an internal combustion engine has a valve operating cam and a rocker arm unit. The rocker arm unit is made up of driving rocker arms which operatively contact the valves, a free rocker arm which is free from contact with the valves, and a changeover mechanism for varying the valve lift amount and timing of opening and closing the valves by connecting the rocker arms and releasing the connection between them. The free rocker arm is urged by a torsion spring so as to operatively contact the valve operating cam. The torsion spring is disposed inside a hollow rocker arm shaft of the rocker arm unit. In case the free rocker arm is fixed to the rocker arm shaft, a coil spring is disposed inside a supporting portion for rotatably supporting the rocker arm shaft such that the free rocker arm is urged by the coil spring via the rocker arm shaft.

Abstract: An SOHC-type valve operating system in an internal combustion engine having a single cam shaft commonly provided for a pair of intake valves and a pair of exhaust valves. A plurality of intake valve driving members are rockably disposed between the cam shaft and the pair of intake valves and have an operative-connection switchover mechanism for switching over the connection and disconnection of the intake valve driving members. A pair of exhaust valve driving members are rockably disposed between the cam shaft and the pair of exhaust valves and independently operate each of the exhaust valves. The operative-connection switchover mechanism includes a switchover pin movable between a position for operatively connecting adjacent intake valve driving members and a position for releasing such connection, which pin is slidably mounted in a cylindrical sleeve secured to the intake valve driving members for guiding the movement of the switchover pin.