Four-stroke cycle internal combustion engine

摘要

A four-stroke cycle internal combustion engine comprises a connecting rod which has an oil dipper at a big-end thereof, a crankcase, a partition wall which surrounds the connecting rod to provide a separation between the crankcase and an oil reservoir and an outer wall which is outward of and surrounds the partition wall and is connected to the partition wall at upper ends thereof so as to define the oil reservoir below the crankcase. A slit is formed in the partition wall below the connecting rod to allow the oil dipper to protrude into and be withdrawn from the oil reservoir to splash oil in the oil reservoir for lubrication by the oil dipper through a swinging motion of the connecting rod. The depth of the oil reservoir is shallower at least in a part of an outer edge area thereof than that below the oil dipper so that a tip of the oil dipper reaches the oil level even when the oil flows into the outer edge area of the oil reservoir.