Camshaft phasing allows the further optimization of performance, fuel economy and emissions without compromising overall engine response and driveability. Variable valve timing also contributes to a reduction in exhaust emissions. It optimizes exhaust and inlet valve overlap and eliminates the need for an exhaust gas recirculation (EGR) system.

The camshaft position actuator is a hydraulic vane-type actuator that changes the camshaft lobe timing relative to the camshaft drive sprocket. Engine oil is directed by a camshaft position actuator oil control valve to the appropriate passages in the camshaft position actuator. Oil acting on the vane in the camshaft position actuator, rotates the camshaft relative to the sprocket. At idle, the camshaft is at the default or "home" position. At this position, the exhaust camshaft is fully advanced to minimize valve overlap for smooth idle. The camshaft position actuator incorporates an integral trigger wheel, which is sensed by the camshaft position sensor to accurately determine the position of the camshaft.

The camshaft position actuator control valve directs oil from the oil feed in the head to the camshaft position actuator. A filter screen protects each oil port from any contamination in the oil supply. During start-up, when little oil pressure is available, an internal spring loaded locking pin keeps the rotor and stator locked together in the home position. When phasing is desired oil pressure is applied to the phaser unlocking the pin.

The camshaft front journal has a drilled oil hole to allow camshaft position actuator control oil to transfer from the cylinder head to the camshaft position actuator. Oil in this oil passage is used to move the camshaft position actuator to the default or home position. The camshaft position actuator is mounted to the front end of the camshaft and the timing notch in the nose of the camshaft aligns with the dowel pin in the camshaft position actuator to ensure proper cam timing and camshaft position actuator oil hole alignment.