A method for monitoring the wear of engine parts without engine disassembly is described. Low level radiation sources implanted in the wearing surfaces serve as a tracer for material loss. Prior to engine testing, controlled wearing of an identical part determines a calibration curve relating wear depth to externally measurable radiation.The results of engine testing show that the method is useful in measuring small amounts of wear in individual engine parts such as piston rings and connecting rod bearings simultaneously without engine disassembly. These tests were performed to evaluate the effectiveness of filters in reducing engine wear. The wear measurements showed that both air and oil filters are highly effective in reducing wear throughout an engine.