Abstract: The present invention provides a piston for a spark-ignition engine, comprising: a land part 18, an upper surface part of which has a crown part 26 forming a combustion chamber; a pair of skirt parts 20 extending downward from a peripheral part of the land part 18 and facing each other in a radial direction thereof; a pair of sidewall parts 19 coupling side end parts of the pair of skirt parts 20 to each other; and a pin boss part 21 that is formed in each of the sidewall parts 19. The present invention can inhibit the generation of HC produced at the time of combustion, while thermally protecting a top ring 30 fitted into a top ring groove 24a on an outer circumferential surface of the land part 18. The crown part 26 is configured by a flat base surface 27 and a bulging part 15 bulging upward above the base surface 27, and a thinned part 40 provided in the land part 18 is formed deep such that the deepest part thereof is positioned inside the bulging part 15.

Abstract: The present invention provides a piston for a spark-ignition engine, comprising: a land part 18, an upper surface part of which has a crown part 26 forming a combustion chamber; a pair of skirt parts 20 extending downward from a peripheral part of the land part 18 and facing each other in a radial direction thereof; a pair of sidewall parts 19 coupling side end parts of the pair of skirt parts 20 to each other; and a pin boss part 21 that is formed in each of the sidewall parts 19. The present invention can inhibit the generation of HC produced at the time of combustion, while thermally protecting a top ring 30 fitted into a top ring groove 24a on an outer circumferential surface of the land part 18. The crown part 26 is configured by a flat base surface 27 and a bulging part 15 bulging upward above the base surface 27, and a thinned part 40 provided in the land part 18 is formed deep such that the deepest part thereof is positioned inside the bulging part 15.