FIELD: piston rings of large-sized two-stroke engines. SUBSTANCE: top piston ring 4 has slot 9 for expansion in mounting; ends of slot prevent gas from escaping from combustion chamber. Grooves 15 are provided on outer lateral surface of ring from its upper end to lower end. Total width of grooves is equal to 0.1 to 1 percent of length of its circumference, mainly 0.2 to 0.5 percent. Grooves 15 limit drop of pressure through ring and reduced its wear. EFFECT: reduction of pressure drop through ring and reduction of its wear. 7 cl, 6 dwg
