FIELD: marine engines. SUBSTANCE: piston is provided with circular fin which is integral with piston head; bearing members made in circular area between side wall of piston provided with outer piston rings terminate in taper wall having passages extending in parallel with piston axis through which cooling oil may flow; taper wall (if viewed on axial section of piston) is connected with side wall by means of rounded-off part of wall. Thickness of wall is reduced in rounded-off part of wall in order to reduce sensitivity to dynamic stresses in area between bearing members and side wall. EFFECT: enhanced efficiency. 3 cl, 2 dwg
