Abstract: A one piece piston for use in an internal combustion engine provided with a plurality of compression rings and oil rings on its circumferential surface includes ring grooves having a hole communicating with an inside of the piston, oil rings received in the ring grooves, respectively; and a keeping ring mounted between the oil rings and having on its internal surface a spring receiving groove whose inner diameter is larger than an outer diameter of a ring type spring, wherein a separation between an external surface of the ring groove and the internal surface of the keeping ring is maintained equal to that of the compression ring and a hole is formed to allow the ring groove to communicate with the inside of the piston.

Abstract: A one piece piston for use in an internal combustion engine provided with a plurality of compression rings and oil rings on its circumferential surface includes ring grooves having a hole communicating with an inside, of the piston, oil rings received in the ring grooves, respectively; and a keeping ring mounted between the oil rings and having on its internal surface a spring receiving groove whose inner diameter is larger than an outer diameter of a ring type spring, wherein a separation between an external surface of the ring groove and the internal surface of the keeping ring is maintained equal to that of the compression ring and a hole is formed to allow the ring groove to communicate with the inside of the piston.