An engine is described having a crankcase, a liner and a head assembly. The crankcase is split along a plane defining a two part crankcase, where fluid passages are passing through only one of the crankcase portions, so as to not require crossing the split line. A connecting rod also includes a tapered end, and the piston has a complementary carrier receiving the connecting rod.

A lubricating structure for a four-stroke engine includes a first oil groove and a second oil groove. The engine includes a crankcase, a cylinder, a cylinder head and an oil pan. The crankcase makes up a crank chamber. The cylinder head is equipped with a valve chamber housing valve driving mechanism. The oil pan is provided on a bottom of the crank chamber. The first oil groove leads mist of the lubricating oil in the crank chamber to the valve chamber by communicating the crank chamber and the valve chamber with each other. The second oil groove leads surplus lubricating oil in the valve chamber to the oil pan in the crank chamber by communicating a lower part of the valve chamber with a neighborhood of the oil pan in the crank chamber. The first oil groove is set smaller in flow path cross-sectional area than the second oil groove.

A valve, an oil separator, and a ventilation system are described. These are used particularly in internal combustion engines, for example for separating oil mist or oil droplets from blow-by gases (crankcase gases). In particular a valve which can be used for example as a bypass valve in a ventilation system is described.

In a breather device of an internal combustion engine, a breather chamber is defined by a head cover main body and a chamber forming member. The breather device includes an upstream breather passage communicating a first end of the breather chamber with a crank chamber, a downstream breather passage communicating a second end of the breather chamber with an intake passage, an oil return passage formed in a cylinder head to communicate a valve actuation chamber with the crank chamber, a first communication hole formed in a lower part of a recessed part of the breather chamber adjoining the first end of the breather chamber to communicate the breather chamber with the valve actuation chamber, and a second communication hole formed in a part of the breather chamber downstream of the first communication hole to communicate the breather chamber with the valve actuation chamber.

An oil separation device of an internal combustion engine includes a gas liquid separation chamber defined by a head cover of the engine, a gas introduction passage connected to a first end of the gas liquid separation chamber at an angle to the first direction, a gas inlet formed in an end of the gas introduction passage remote from the gas liquid separation chamber, and a gas outlet formed in a second end of the gas liquid separation chamber. Oil splashed from a valve actuating chamber of the engine is prevented from entering the oil separation device, and oil mist can be effectively separated from blow by gas.

An oil separator for separating an oil in a blow-by gas, includes a housing forming a flow passage, and defining an annular shoulder face facing a downstream side; a valve member reciprocatable between a blocking position abutting an end face thereof against the annular shoulder face to block the flow passage, and an open position separating the end face from the annular shoulder face to open the flow passage; a spring device urging the valve member toward the blocking position; and a reflux device for refluxing the oil separated from the blow-by gas. The valve member includes a first side face facing a wall face of the flow passage and spaced from the wall face at a predetermined interval. A relation wherein a gap between the end face of the valve member and the annular shoulder face in the open position is narrower than the predetermined interval is always established.

Provided is an oil separator having a high efficiency in removing oil particles of relatively large sizes. A blow-by gas passage of the oil separator (2) includes an upstream passage (18) and a downstream passage (20) extending at an angle to the upstream passage. A separation wall (36) provided in the downstream passage includes a first surface (40, 78) forming an obtuse angle relative to the upstream passage, and a second surface (42) adjoining the first surface on a downstream side thereof and defining a planar surface extending substantially perpendicularly to the upstream passage. The blow-by gas is accelerated in the upstream passage, and the flow direction of the blow-by gas is changed by the first surface without substantially changing the flow speed and without disturbing the flow before the blow-by gas flows along the second surface. At this time, the oil particles in the blow-by gas collide with and are trapped by the second surface owing to the inertia of the oil particles.

A blow-by gas passage structure is provided inside a separator chamber that is formed between a cylinder head cover and a baffle plate joined to the cylinder head cover by vibration welding. A first rib is provided on the opposite surface of one member of the cylinder head cover and the baffle plate, while a second rib is provided on the opposite surface of the other member, at positions upstream of the first rib in the flow of the blow-by gas and adjacent a gap formed between the distal end of the first rib and the opposite surface of the other member. The second rib has a height that is equal to or larger than the height of the gap so as to prevent passing of the blow-by gas through the gap.

A breather device includes: a breather chamber into which oil mist in a crank chamber of a combustion engine is introduced; and a breather passage configured to guide oil mist from a crank chamber into the breather chamber. The breather chamber has formed therein a labyrinth structure in which gas-liquid separation of the oil mist is performed. An introduction pipe forming a part of the breather passage is communicated with an upper portion of the crank chamber, and projects upward from an upper end portion of the crank case.

To provide a running gear structure of an internal combustion engine capable of reducing the size of the internal combustion engine. In a running gear structure of an internal combustion engine including a supercharger and a supercharger driving mechanism transmitting power to the supercharger and driving the supercharger, the supercharger driving mechanism is provided with driving force transmission members (a third intermediate gear and a fourth intermediate gear) disposed on a side opposite to cylinders of the internal combustion engine across valve trains driving a valve gear using, as a power supply, driving force of the crankshaft rotated by explosion in the cylinders. The valve train is disposed closer to an inner side of the internal combustion engine.