sprocket wheel 10 by meshing engagement of the chain or belt with the teeth or friction pads 18 of the sprocket spur and or friction gears 12 which are each constrained by one way clutches not shown in their centers to rotate in one direction centrally of the sprocket wheel 10 is a shaft 20 upon which the sprocket wheel 10 is mounted for rotary motion the portions 22 of the assemblies that move radially tend to form uniform effective diameters and tend to be equidistant of the center of the sprocket wheel 10 and mechanically are kept that way by a regularly disposed collection of linear linkage guides such as telescoping rods 24 and sleeves 26 shown in fig1 and a single association of rod and sleeve in greater detail in fig3 an alternative method is shown in fig4 in which a series of intermeshed sprocket or spur gears 48 are arranged circumferentially around sprocket wheel 10 near the circumference so as to intermesh with one another and also simultaneously mesh with arm 22 which has been suitably modified for operation in this embodiment with a series of teeth along each side as in the commonly known rack and pinion arrangement these equalizing assemblies may be attached anywhere on the piston and rod assemblies and may incorporate additional structure for attachment a flange 28 is mounted on the portion 22 of the assembly that moves radially on the sprocket.