Abstract: On the upper portion of a cylinder head 1 of an engine mounted on a vehicle body in such a way that a crankshaft faces in the lateral direction of the body, a head cover 36 is supported in a floating state through an elastic member 14 and a rubber bush 52. A pair of TDC sensors 37i and 37e for detecting the rotational positions of engine camshafts 6i and 6e, are attached from the outside to the front surface and to the rear portion of the upper surface of the head cover 36 with bolts 38 respectively in such a way as not to interfere with a bonnet 39 of the body descending forward. Consequently, while ensuring the maintainability of the TDC sensors 37i and 37e of the engine, the TDC sensors 37i and 37e can compactly be attached to the engine.

Abstract: A first thrust limiting member and a second thrust limiting member are provided on a cam shaft rotatably carried between a lower cam shaft holder and an upper cam shaft holder which are fixed to an upper surface of a cylinder head 1, so that the first and second thrust limiting members and abut against the cam shaft holders 9.sub.5 and 10.sub.5. The second thrust limiting member has a plurality of detected projections provided around of an outer periphery thereof, so that the detected projections are detected by a TDC sensor 37 mounted to a head cover of the engine. Thus, the rotated position (phase), the angle of rotation and the number of rotations of an rotary shaft of an engine such as a cam shaft 6e and a crankshaft can be detected with good accuracy in a structure including a decreased number of parts, and the axial dimension of the rotary shaft of the engine can be reduced.