- Valves lifters are also referred to as cam followers or tappets.
|Fig. 2.18 (Left "a" & right "b')|
- With the engine valve closed, there is no load the on the lifter, and the plunger is held upwards by the spring.
- Oil from the oil gallery enters the lifter through holes in the lifter body and plunger.
- They oil pressure forces the check valve open to keep the chamber below the plunger full (figure 2.18 (a)). This removes lash from the valve train.
- As the cam rotates and raises the lifter, the check valve closes to trap the oil in the chamber below the plunger.
- The lifter moves upward as an assembly, as shown in the figure 2.18(b), to open the engine valve in the usual way.
- As the cam continues to rotate, the lifter moves down words to close the engine valve, and the force on the plunger is relieved. Any oil lost from the chamber is replaced by oil through the check valve.
- The chamber is designed to have a slight leak past the plunger. This acts as a lubricant between the plunger and body, and also enables the air to be bled from the lifter.