Abstract: An internal combustion engine comprises a cylinder block including a front wall, and a chain cover attached to the front wall. Coolant passage walls defining a coolant passage are integrated with the front wall of the cylinder block and the chain cover, respectively. Heat insulating means are arranged to prevent a contact of lubricating oil and blow-by gas with the coolant passage walls.

Abstract: An oil pan for an internal combustion engine having an engine lubrication system. The oil pan comprises a shallow bottom section and a sump section. A guide plate is secured at an inner surface to which a crankshaft splashes lubrication oil carried into the shallow bottom section. The guide plate having an inclined and a guide parts extends generally along the axis of the crankshaft and extends generally parallel with a horizontal plane. The inclined part which gradually becomes high in level in the direction toward the sump is continuously connected to the inclined part to be formed in a generally arcuate shape. Therefore, the splashed oil at the inner surface cannot over the guide plate, and the oil is positively returned into the sump section by the guide plate. Accordingly, lubrication in this engine is smoothly carried out without causing a lack of the oil in the sump section.

Abstract: An internal combustion engine is equipped with a crankcase ventilation system in which fresh air flows through a crankcase. The cylinder block of the engine is formed with a fresh air suction port whose one end is opened to the chamber of a crankcase in order to establish communication between a rocker cover chamber and the crankcase chamber. The one end of the fresh air suction port is located in the vicinity of the peripheral surface of a counterweight of a crankshaft. The rotation of the counterweight develops vacuum thereby to suck fresh air from the rocker cover chamber through the fresh air suction port into the crankcase chamber, thereby effecting ventilation in the crankcase.