<p>A noise-reducing pulley arrangement is described. The pulley (16) has a plurality of recesses (24) and a plurality of flat surfaces (25) which are arranged alternately in the circumferential direction. A boundary (27) locating between each recess (24) and each flat surface (25) extends in the radial direction of the pulley (16). When pistons in cylinders of the engine reach the top dead points respectively, the direction of the corresponding boundary (27) conforms with the direction in which the piston force acts upon the shaft (15). <IMAGE></p>
