All engines covered herein are equipped with hydraulic cam followers, which Do NOT require clearance adjustment. If a 'ticking' noise is heard from the cylinder head while the engine is operating, the cause is usually air or small particles trapped within the cam followers themselves. This prevents oil pressure inside the follower, and causes the 'ticking' sound. In some cases, an engine 'flush' treatment can cure this annoying problem. If a hydraulic lifter (or multiple lifters) fails to quiet after an engine flush treatment, it may need to be replaced.