sprocket 12 tooth engages with the continuous synchronous belt 16 the orbiting sprocket 12 tooth profile is a function of the constrained diameter of the continuous synchronous belt 16 fixed within the circular mounting flange 7 consequently a different constrained continuous synchronous belt 16 diameter will produce a different orbiting sprocket 12 tooth profile for instance a continuous synchronous belt 16 having a diameter of 4 470 inches would preferably have the orbiting sprocket 12 tooth profile shown in fig1 a 11b an eccentric counterweight 2 is fixedly mounted on the sprocket end 14 of the sprocket shaft 15 and has a rod journal end 28 a counterweight end 29 and a rod journal receptacle 1 a rod journal 13 is rotatably mounted within the rod journal receptacle 1 of the eccentric counterweight 2 the rotation of the eccentric counterweight 2 and crank arm counterweight 30 are interdependent and must be appropriately balanced and positioned to facilitate the proper functioning of the unit the relationship between these components requires adjustment of the apparatus during final assembly in order to properly balance the apparatus a mass or combination of masses is positioned on the counterweight end 29 of the eccentric counterweight 2 this can be accomplished by affixing a counterweight mass 33 to the eccentric counterweight 2 or by fabricating a one piece eccentric counterweight 2 with an appropriate mass on the counterweight end 29 referring now to fig1 in the balancing process the eccentric counterweight 2 is first rotated about its center of gravity and observed for imbalance the counterweight mass 33 is increased and or moved along.