Abstract: A device for forcing a piston ring, which is a sealing member between the bore wall of a cylinder and the cylindrical outer surface of a piston, radially outwardly. The head of a plunger which forces the piston ring radially outwardly is semispherical and a sustantially conical hole for receiving therein the semispherical head of the plunger is formed in the inner peripheral surface of the piston ring in opposed relationship with the piston. Even when the axis of the plunger is misaligned when the center line or axis of the substantially conical hole, it can force the piston ring radially outwardly without producing any excessive force leading to the failure of the plunger and/or piston ring.

Abstract: A device for forcing a piston ring, which is a sealing member interposed between the cylindrical outer surface of a piston and the bore wall of a cylinder, radially outwardly beyond the cylindrical outer surface of the piston. A plunger rod which forces the piston ring radially outwardly is extended through a coiled spring. One end of the coiled spring is enlarged in diameter and is made into engagement with the edge surface of a radial hole into which is inserted the coiled spring while the other end of the coiled spring is made into engagement with the inner end of the plunger rod, whereby the piston ring is forced to extend radially outwardly by the compressive force of the coiled spring acting on the piston ring through a plunger.