PURPOSE: To expedite the spontaneous operation of a grinding wheel cutting edge without affecting the performance of an engine at the time of honing processing on cylinder inner periphery surface.

CONSTITUTION: A diameter expansion groove portion 6 is formed by conducting diameter expansion locally with a portion which is more on a crankshaft side than the final piston ring 9 of a piston 4 that is at a bottom dead point position and which also faces both end surfaces of a piston pin 10, out of a cylinder inner periphery surface 5 as a center. The spontaneous operation of a cutting edge of grinding wheel is expedited when the passes the grinding wheel edge 12 of a diameter expansion portion 6 repeatedly at the time of honing processing.