A plurality of heat receiving ribs are projected inwardly from the inner
wall surfaces of a crankcase of a splashing oil lubrication type internal
combustion engine. The heat receiving ribs extend in the same direction of
a crankshaft so as to easily absorb heat from splashed engine oil. As a
result, the temperature in the crankcase is reduced, thereby the
lubrication characteristic of the engine oil can be maintained in good
condition.
