RECIPROCATING ENGINE

A reciprocating engine (1) includes a cylinder (2); a piston (3) reciprocating in the cylinder (2) in a direction X; a connecting rod (5) rotatably coupled at its small end portion (4) to the piston (3) through a piston pin (4a); ring grooves (7, 8) disposed adjacent to each other in the direction X and formed in a peripheral side surface (6) of the piston (3); piston rings (9, 10) respectively fitted in the ring grooves (7, 8); partitioning means (14) for partitioning an annular space (11) between the piston rings (9, 10) into a thrust side semiannular space (12) and an anti-thrust side semiannular space (13); and communicating means (16) for allowing the space (12) to communicate with a combustion chamber (15) where a fuel-air mixture is burned.