Piston Ring Museum

Piston Ring Function

B-3 Ring Design Criteria

The following are some of the questions that must be addressed before designing a properly functioning ring:

  1. Does the finished piston ring conform to the cylinder walls of the engine? Even a tiny gap between the ring's running face and the cylinder wall will provide a leakage path for hot combustion gases and/or engine oil.
  2. Does the ring press against the cylinder wall with enough force to generate the necessary unit pressure *1
  3. Can the chosen ring material withstand extremely hot combustion gases?
  4. Is the ring material also resistant to corrosive attack by the hot exhaust gases?
  5. Can the ring withstand a high-speed operation without losing performance?
  6. Does the ring avoid improper movement (i.e., not 'pounding out' its groove in the piston)?
  7. Is the ring scuff-resistant, even at the upper point of the piston and cylinder, where lubrication is very poor and friction force is very high?
  8. Does the ring show adequate life characteristics, i.e., even when the engine is being operated at 2,000 to 3,000 rpm, the ring must last many thousands of operating hours (= years!)?
  9. Can the ring survive the bitterest cold in very cold climates and also the highest temperatures in very hot climates?
  10. Does the ring perform its function well without generating too much friction?

The rings are checked and tested against these criteria again and again before they are approved for installation in a production engine.

  • *1 Pressure exerted in the direction of the cylinder wall radius