Four-stroke cycle internal combustion engine

A four-stroke cycle internal combustion engine comprising:

• a connecting rod having a big end;
• an oil dipper provided at said big-end of said connecting rod;
• a crank shaft;
• a crankcase in which said crank shaft is disposed;
• an oil reservoir below said crankcase, said oil reservoir having an oil level;
• an outer wall which is outward of and surrounds said partition wall and is connected to said partition wall at upper ends thereof so as to define said oil reservoir below said crankcase, said outer wall having a portion located opposite to said partition wall;
• and
• a slit formed in said partition wall below said connecting rod to allow said oil dipper to protrude into and be withdrawn from said oil reservoir to splash oil in said oil reservoir for lubrication by said oil dipper through a swinging motion of said connecting rod;
• wherein in a vertical cross-section including an axial line of said crankshaft, an outer edge area of said portion of said outer wall is upwardly inclined toward said oil dipper so that said oil reservoir has a depth that is shallower at least in said outer edge area thereof than that below said oil dipper, whereby a tip of said oil dipper reaches the oil level to said oil reservoir even when the oil flows into said outer edge area of said oil reservoir.