Oil from the oil gallery flows into the cylinder heads through an external oil line. The oil flows up through the rocker arm pedestal, to the rocker arm, down through the push rods, to the hydraulic lifters.
When the lifter begins to roll up the cam lobe, the check valve is held against its seat in the plunger by the check valve spring that traps the oil in the base of the lifter body below the plunger. The plunger and lifter body then raise as a unit, pushing up the push rod to open the valve. The force of the valve spring, that is exerted on the plunger through the valve lever and push rod, causes a slight amount of leakage between the plunger and lifter body. This leak-down" allows a slow escape of trapped oil in the base of the lifter body. As the lifter rides down the other side of the cam lobe and reaches the base circle or valve closed" position, the plunger spring quickly moves the plunger back (up) to its original position. This movement causes the check valve to open against the check valve spring and oil is replenished. This restores the lifter to zero lash.
To determine if replacement or repair of the hydraulic lifter is necessary, perform the following procedure. See Figure 28407 .
Flowchart for Replacement of Hydraulic Lifters
Remove the hydraulic lifters as follows:
Clean the hydraulic lifters as follows:
To avoid personal injury when blow drying, wear adequate eye protection (safety glasses or face plate) and do not exceed 276 kPa (40 lb/in. 2 ) air pressure.
Inspect the hydraulic lifters as follows:
Install the hydraulic lifter as follows: