All engines covered by this manual are equipped with hydraulic valve lifters. Valve systems with hydraulic valve lifters operate with zero clearance in the valve train, and because of this, the rocker arms are usually nonadjustable. The only means by which valve system clearances can be altered is by installing 0.060 in. (1.5mm) over or undersize pushrods; but, because of the hydraulic lifter's natural ability to compensate for slack in the valve train, all components of the valve system should be checked for wear if there is excessive play in the system.
When a valve in the engine is in the closed position, the valve lifter is resting on the base circle of the camshaft lobe and the pushrod is in its lowest position. To remove this additional clearance from the valve train, the valve lifter expands to maintain zero clearance in the valve system. When a rocker arm is loosened or removed from the engine, the lifter expands to its fullest travel. When the rocker arm is reinstalled on the engine, the proper valve setting is obtained by tightening the rocker arm to a specified limit. But with the lifter fully expanded, if the camshaft lobe is on a high point it will require excessive torque to compress the lifter and obtain the proper setting. Because of this, when any component of the valve system has been removed, a preliminary valve adjustment procedure must be followed to ensure that when the rocker arm is reinstalled on the engine and tightened, the camshaft lobe for that cylinder is in the low position.