Figure 3-32. - Types of piston rings.

The four-ring piston has three compression rings from the top, followed by one oil control ring. Commonly used on diesel engines because they are more prone to blow-by. This is due to the much higher pressures generated during the power stroke.

The four-ring piston has two compression rings from the top, followed by two oil control rings. The bottom oil control ring may be located above or below the piston pin. This is not very common in current engine design.

Figure 3-33. - Configurations of piston rings.