Abstract: This cam has a cam lobe having opposite sinusoidal surfaces which have two rises and two reverse rises or two dips in 360.degree. of each sinusoidal surface with the rises in one such surface being opposite to the reverse rises in the other such surface, which sinusoidal surfaces will have full, centerline contact with a pair of bearings attached to the same connecting rod connected to a pair of pistons, these bearings being on opposite sides of the cam lobe and at one time being driven in one direction by one of the two pistons in each pair and then at another time in the opposite direction by the other piston in that pair. The surfaces of the cam lobe avoid friction or binding between the cam lobe surfaces and across the width of each bearing continuously through each revolution of the cam and of each bearing.