1. Piston Rings

LO 7-05: Identify and explain the purpose and functions of piston rings, their construction features, and their ring shapes according to ring function.

 

Piston Rings

Piston rings are among the most critical components for engine durability and efficient operation. Worn rings cause high oil consumption and a loss of compression that results in low power and excessive blowby Figure 27. Rings, along with cylinder walls, will wear faster than other internal engine parts, which limit engine life. In fact, one of the primary determinants of engine life is the ability of the piston rings to work efficiently. Long ring life is a function of ring design, maintenance practices, and proper engine operation.

Piston Ring Functions

Piston rings must perform the following jobs under extreme temperatures for the life of the engine:

  • Form a gas-tight seal between the piston and the cylinder wall: Gas-tight sealing of the cylinder is necessary to provide adequate compression pressure. It also minimizes blowby, which reduces power and leads to oil contamination and excessive crankcase emissions. An oil film on the cylinder walls enhances the sealing between the ring and the cylinder wall.
  • Assist in cooling the piston: Piston rings transfer heat to the cylinder wall, which helps keep pistons cool.
  • Apply a film of lubrication oil on the cylinder wall: Piston rings must apply a film of oil that provides adequate lubrication properties. However, the film of oil cannot be excessive and thus cause high oil consumption and increased emissions.
  • Form a compatible, replaceable wear surface with the cylinder wall: Piston rings must be compatible with the cylinder wall. Compatibility is a property that allows two metals to slide against one another with minimal friction or wear.
   Fig07_27

FIGURE 07-27: Piston rings provide a gas-tight seal in the cylinder to minimize loss of compression and blowby.

 

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