System for controlling valve shift timing of an engine

A system for controlling a valve-shift-timing of an engine, comprising:

• a cam shaft arranged so as to be rotatably driven by an output shaft of the engine;
• a swingable cam disposed so as to be swingable for lifting at least one of an intake valve and an exhaust valve in accordance with a pivotal movement of said swingable cam upon at least one of a direct and an indirect abutment with said at least one of said intake valve and said exhaust valve;
• a rotatable cam disposed on said cam shaft so as to be rotatable integrally with said cam shaft and to move said swingable cam pivotally in accordance with rotation of said cam shaft;
• a transfer means for transferring said rotatable cam in an axial direction in which said cam shaft extends;
• and
• a rotational phase changing means for changing a rotational phase of said rotatable cam relative to said output shaft in accordance with the movement of said rotatable cam by said transfer means;
• wherein each of an abuttable surface of said swingable cam and an abuttable surface of said rotatable cam is of a shape tapered in the axial direction in which said cam shaft extends;
• and
• said rotatable phase changing means is disposed on a portion other than said swingable cam.