Patent ID: 8430076

Claim:
An engine comprising: a crankshaft supported on a crankcase; a valve-operating camshaft supported on a cylinder head; a rocker shaft disposed adjacent to and parallel with the camshaft, wherein the camshaft is disposed between the crankshaft and rocker shaft and the rocker shaft swingably supports an intake rocker arm and an exhaust rocker arm and has opposing ends directly supported by first and second support holes defined in opposing walls of the cylinder head; a timing transmission system which includes a drive rotation member fixedly mounted to the crankshaft, a driven rotation member fixedly mounted to the camshaft, and an endless power transmission member wound around the two rotation members, and which provides connection between the crankshaft and the valve-operating camshaft; an access window through which the driven rotation member is attached to and detached from the camshaft being opened in an outer end surface of the cylinder head, and a lid body for closing the access window being jointed to the outer end surface of the cylinder head, a first match mark indicated on an outer side surface of the driven rotation member; a second match mark indicated on an engine main body to coincide with the first match mark when the crankshaft is in a predetermined rotational position; a bolt hole provided in an end wall of a hub of the driven rotation member which is fitted into an end portion of the camshaft; a positioning groove extending radially from the bolt hole; a positioning pin projectingly provided on an end surface of the camshaft in a position eccentric from a center of the end surface in a certain direction, and engaged with the positioning groove when the camshaft is in a predetermined phase relationship to the crankshaft in the predetermined rotational position; a threaded hole which is provided on the end surface of the camshaft and corresponds to the bolt hole when the camshaft is in a predetermined phase relationship to the crankshaft in the predetermined rotational position; and a mounting bolt penetrating through the bolt hole and screwed into the threaded hole to fix the hub to the camshaft; wherein the outer end surface of the cylinder head comprises a slanted surface which is inclined so that at least a part of an outer periphery of the driven rotation member on a side opposite from the drive rotation member is exposed from the access window.