Apparatus and method for assembling a piston ring in a circumferential groove of a piston wherein a plurality of ring nest members are disposed about a common axis for radial movement toward or away from the axis between radially contracted positions and radially expanded positions. The nest members collectively form a circular opening concentric with the axis and a ring-receiving recess concentric about the opening when they are in the contracted positions. The recess locates a radially unexpanded ring concentric with the axis and has a fixed axial dimension for preventing "oil canning" of the ring when it is expanded. The ring nest members are movable from the radially contracted to the expanded positions when the ring is expanded so as to collectively enlarge the opening for receiving the piston and the recess to maintain the expanded ring substantially concentric with the axis while the fixed axial dimension prevents "oil canning". A plurality of radially and axially movable ring expanding fingers are disposed about the axis and positionable in the opening for radially expanding the ring while it resides in the recess. Expansion of the ring effects movement of the ring nest members radially outward to the expanded positions to collectively enlarge the opening. The piston is moved into the enlarged opening along the axis in a manner that the ring expander fingers are moved axially out of engagement with the expanded ring in the enlarged recess while the piston groove is moved to receive the expanded ring from the recess. <IMAGE>
