Oil ring with coil expander

A piston ring comprising:

• an oil-scraping oil ring, made of steel, having a generally I-shaped cross-section consisting of upper and lower side rails which are mass of rigidity and a thin web for connecting the upper and lower side rails, the thickness of said web being not more than 0.8 mm, said web having a large number of oil vent holes punched along a periphery thereof, said upper and lower side rails and web defining an outer peripheral channel for receiving oil scraped and an inner peripheral groove for receiving a coil expander, said side rails having inclined flat surfaces, in the cross-section, converging to a peripherally extending center line of the web, so as to define the trapezoidal inner peripheral groove, said annular coil expander located in said inner peripheral groove and bearing against the upper and lower side rails substantially at two points, in the cross-section, said coil expander being spaced from the web of the oil ring to provide a slight gap therebetween.