A drive transmission, having two counter-rotating cams bearing-mounted within a housing about a rotational axis. The counter-rotating cams have asymmetrical lobe profiles which are operative to drive a corresponding pair of coaxial drive shafts in opposite directions along the rotational axis. The asymmetry of the lobe profiles prevents the cams from locking when the lobe apexes pass the top and bottom dead center positions relative to the follower or drive pins.