Reasons for maximum wear at top of the stroke being:
- The gas load behind the ring is maximum
- It is the hottest region
- Viscosity of oil film is low and liable to breakdown under heavy load and high temperature
- Abrupt Change in direction of piston rings, at dead ends of reciprocating motion.
- Corrosive wear
- More liable to be attacked by acids.
Reason of maximum wear around the ports.
- Due to leakage of hot gases past the top ring into the ports and these hot gases will tend to burn off the oil film.