Piston Ring Museum

Piston Ring Function

B-6 Oil Ring

Engine lubricating oil performs an essential protective function in the engine by allowing parts to slide and by preventing them from making direct metal-to-metal contact (reducing friction *1), which causes wear, and in the worst case, total engine failure. Engine oil reduces operating friction, making the engine more efficient; while also serving to cool critical engine components and trapping harmful dirt particles.

Appearance of the Oil Ring

Appearance of the Oil Ring

Can you see how it is assembled? This 3-piece oil ring is installed into the piston groove and functions as an assembly to generate the required performance. The oil ring assembly above has a diameter of 86mm, an axial width of 2.0mm and a radial thickness of 2.5mm.

Cross-Sectional Shape of the Oil Ring Side Rails

The thin, upper and lower plate-shaped rings are referred to as side rails. Each side rail is about 0.4mm wide. Each oil ring assembly requires two side rails: an upper side rail and a lower rail. The periphery of each side rail makes contact with the cylinder walls and slides. A hard film of CrN (nitrided chromium) has been applied to the running face by a PVD process. Other surface treatments for the side rails' running face include nitriding and hard chrome plating.

Appearance of the Oil Ring Spacer expander

The wave design seen in the picture below allows the spacer expander to act as a spring. The spring action of the spacer expander presses the side rails against the cylinder wall until the correct tension and unit wall pressure are achieved.

Oil Ring

As mentioned above, the two side rails and the spacer expander form an oil ring set or assembly. This is why it is referred to as a three-piece ring.

2 Piece Oil Ring

The oil ring illustrated above is a two-piece assembly that is used most often for diesel engines and some of gasoline engines applications. We refer to this ring as a oil ring assembly. This oil ring assembly consists of a M-shaped steel rail and a cylindrical coil spring. The DVM is characterized by its lightweight, high conformability and its ability to accurately control oil and reduce oil consumption.

2 Piece Oil Ring

  • *1 Friction that occurs when the outer periphery of the piston ring rubs the inner periphery of the cylinder