The frictional force measuring method of a piston-piston ring cylinder system at engine operation condition by using floating liner method has some device structures, such as using plural one dimensional load cells (load washer) and six or eight three-component (triaxial) force sensors method. However, in some cases the qualitative and quantitative values of the measured data differed due to differences in the structure of the device, differences in settings and differences in the method of processing the measured data. This research described a typical device structure of the floating liner engine, and described the case of the operation data processing method of piston frictional force, the reproducibility of data, and the zero point of frictional force. Furthermore, by the combustion pressure seal method of the floating liner, it showed clearly that momentary swing back force occurs in a frictional force curve and considered the cause.

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