Abstract: An internal combustion engine having a crankcase ventilation system is shown. The engine comprises a cylinder block and an oil pan which are assembled to define a crankcase. A crankshaft is rotatably held in the crankcase and including a counterweight. The cylinder block is formed with a fresh air inlet passage through which the interior of the crankcase and the outside of the engine are communicated. The fresh air inlet passage has a fresh air inlet opening which is exposed to the interior of the crankcase at a position close to the counterweight so that under rotation of the crankshaft, the opening is periodically covered and opened by the counterweight. A blow-by gas passage is provided through which the interior of the crankcase and the outside of the engine are communicated. The opening of the fresh air inlet passage is covered by the counterweight when the passage in the crankcase becomes relatively high, and opened by the same when the pressure in the crankcase becomes relatively low.

Abstract: To reduce the size and weight and the number of parts required for a chain cover apparatus for an engine, the chain cover for covering a chain for transmitting a rotational force of a crankshaft to at least one camshaft mounted on a cylinder head comprises a chain cover formed with a cylindrical hollow projection portion extending frontward and having a hole through which the crankshaft is passed, and an oil pump accommodated within the cylindrical hollow projection portion and driven by the crankshaft. Further, the chain cover is formed with a semicircular flange portion formed at a lower wall of the cylindrical hollow projection portion so as to be joined with an oil pump, and with two flat flanges formed on both sides of the cylindrical hollow projection portion so as to be joined between the oil pan and the engine block.

Abstract: An internal combustion engine is disclosed, which comprises a cylinder block having lubrication oil passages formed therein, the oil passages having a cylinder block opening at one longitudinal end of the cylinder block; a crankshaft operatively installed in the cylinder block, the crankshaft having one end portion exposed to the outside of the cylinder block from the one longitudinal end of the same; and a front cover structure attached to the one longitudinal end of the cylinder block.

Abstract: A camshaft driving arrangement for a DOHC engine comprises two pairs of sprockets, each pair being mounted to the adjacent pair of camshafts, and two idler gears rotatably mounted to the cylinder banks, respectively. A timing chain drivingly interconnects the crankshaft and the two idler gears. On the other hand, two camshaft driving chains each interconnect one of the two idler gears and the adjacent two cam sprockets. A front cover is so constructed and arranged as to conceal the two idler gears and the timing chain.

Abstract: A cylinder block includes two cylinder banks angularly disposed to each other, and two cylinder heads are mounted on the two cylinder banks, respectively. Two idler gears are rotatably mounted to the two cylinder banks, respectively, and a crankshaft is rotatably mounted to the cylinder block. A chain drivingly interconnects the two idler gears and the crankshaft. The chain, the idler gears, and the crankshaft cooperate with each other to define a predetermined space adjacent to the cylinder block, wherein an auxiliary device is mounted.