Oil ring assembly

In a compound steel oil ring assembly comprising a pair of annular side rails having an inner and outer circumferential surface and a spacer expander located between said rails for spacing the rails apart and having a plurality of spaced shoulders having a substantially flat axially and radially presented front face with a circular arc profile in plan view of the expander, the faces being in contact with the inner circumferential surface of the rails for urging the rails in a direction toward their outer circumferential surface, the improvement wherein the faces of the shoulders of the spacer expander in contact with the rails have a plurality of grooved-shaped corrugations in them and the inner circumferential surface of each side rail that contacts said face of the shoulders of said spacer expander has a plurality of groups of spaced, groove-shaped corrugation lines therein, the lines of each group being arranged to intersect each other and being alternately inclined at an angle parallel to lines tangent to the circular arc profile of the face of the shoulders.