Slider-crank mechanisms used in open/close motion from toggle positions can be driven at the crank by many devices. Usually, the slider motion is defined first to synthesize crank motion. When slider motion has acceleration continuity only, crank acceleration is discontinuous causing shock loading at high speeds. To avoid such behavior, motion constraints must be assigned up to ping continuity at the limiting positions. This paper presents kinematic motion equations of slider-crank mechanisms with input from both the slider and crank. Toggle and limiting positions having required transmission angles at varied link ratios are determined. Motion functions that yield continuous crank acceleration are demonstrated.