The radiotracer technique of surface layer activation was used to study piston ring wear rates in the Detroit Diesel Allison “Series 60” engine. Radioactive 54Mn was induced in the chromium surface of the ring face by bombardment with an α beam from a particle accelerator. Wear of the piston ring surface was determined by measuring the accumulation of radioactive debris in the oil during engine operation and by measuring the radiation intensity of the rings from outside the engine between intervals of engine operation.Information was obtained on the wear rate of the top compression ring during break-in and as a function of engine speed and power output. In addition, piston rings activated around their entire circumference were used to determine wear as a function of angle from the ring gap. The collection efficiency of the oil filtration system, for ring wear debris was also determined by measuring radioactivity in the oil filters.The technique of surface layer activation has been shown to be capable of very high sensitivity for the measurement of piston ring wear in real time. Data from a wide range of operating conditions have been used to determine the wear characteristics of this component critical to engine durability.