Variable valve mechanism, engine, and automatic two-wheeled vehicle

A variable valve mechanism which changes an opening/closing timing of an intake valve or an exhaust valve in response to an engine rotation speed, the variable valve mechanism comprising:

• a cam sprocket which rotates in response to a rotation of a crank shaft;
• a cam shaft which is integrated with any one of intake side and exhaust side cams and is provided to be rotatable relatively to the cam sprocket;
• and
• a link member that engages with the cam sprocket and the cam shaft and transmits a rotation from the cam sprocket to the cam shaft, wherein
• the link member is supported by the cam sprocket to be swingable and swings in response to a change in rotation speed of the cam sprocket to rotate the cam shaft relatively to the cam sprocket,
• the link member includes:
• a swing shaft which is fixed to the cam sprocket;
• a weight portion which is disposed to be separated from the swing shaft;
• and
• an engagement portion which engages with an engagement pin provided in the cam shaft and transmits a rotation of the cam sprocket to the cam shaft;
• the link member is supported by the cam sprocket to be swingable;
• and
• the weight portion moves outward in a radial direction of the cam sprocket and the engagement portion moves to move the engagement pin in accordance with the rotation of the cam sprocket so that the cam shaft rotates relatively to the cam sprocket;
• the engagement portion is formed as a groove having an inner wall surface, and
• the groove is provided with a first holding position which receives the engagement pin while the link member does not swing to a predetermined position or more and a second holding position which receives the engagement pin while the link member swings to a predetermined position or more,
• a first stopper portion is provided in the inner wall surface disposed at a farther side from the swing shaft in a vicinity of the first holding position, and
• the first stopper portion protrudes toward the inner wall surface facing the first stopper portion.