Development of measurement apparatus of piston assembly friction in a small motorcycle engine

This study developed a friction measurement apparatus with a floating cylinder liner, in a small motorcycle engine. In this measurement apparatus, joint plates were installed in the grooves on the outer periphery of the floating liner, and then the plates, as well as load washers of piezo type were mounted in the cylinder block, at both the thrust and the anti-thrust sides. A stepped ring, protruding inward, was mounted on the top of the floating liner so that cylinder pressure acting on the stepped portion was balanced in the vertical direction. Thus, it was possible to measure the friction in the sliding directions of the piston. Using this apparatus, the effect of engine operating period on friction was investigated, in a piston micro-dimpled with a fine particle bombarding process. Results indicated that, at low engine speeds, friction decreased with operating period, but at high engine speeds, friction decreased after 10 hours of operation, then increased after 20 hours of operation.