The invention discloses a crankshaft box. The crankshaft box is provided with a lubricating oil splashing hole channel which enables the crankshaft box and a rocker arm installation space of an engine air cylinder assembly to communicate. According to the crankshaft box, splashing lubricating oil in the crankshaft box enters the rocker arm installation space through the lubricating oil splashing hole channel, a rocker arm, an air valve and other cylinder head moving parts can be fully lubricated and cooled, the circulation route of the lubricating oil is not changed, and rapid abrasion to the rocker arm and the air valve and carbon deposition caused by high temperature are avoided, so that the service life of a rocker arm assembly is prolonged.