A four-stroke engine includes an oil tank, a crankshaft chamber, a distribution chamber, a rocker chamber, a combustion chamber, and a lubricating system. The oil tank is communicated with the crankshaft chamber through an oil supply channel. The four-stroke engine further comprises a cam and a transmission mechanism connected between the cam and a crankshaft of the crankshaft chamber in a matched manner. The cam is matched with a rocker of the rocker chamber and located above the combustion chamber.

A piston pin is provided that includes a pin oil channel to which oil is supplied from the connecting rod. A piston is provided that includes a pin boss, an oil groove formed in a pin bore surface, and a communication oil channel that connects a cooling channel that is provided closer to a combustion chamber than the piston pin and the oil groove to each other. The pin oil channel opens in the outer surface of the piston pin at a point corresponding to the oil groove. In the view of the piston from the direction of the piston pin axis, the oil groove is formed in the pin bore surface at a position closer to a crankcase than a second straight line and is not formed in a part of the pin bore surface that is closer to the combustion chamber than the second straight line.

A small end of a connecting rod includes an oil supply hole extending from an outer surface to an inner surface of the small end. The oil supply hole includes an oil storage groove and a communication hole. The oil storage groove is recessed from the outer surface and extends along the circumference of the small end. The communication hole extends through a bottom surface of the oil storage groove and connects the outer and inner surfaces. Opposite edges of the oil storage groove contact the outer surface in a direction the oil storage groove extends. The bottom surface of the oil storage groove has an opening contacting a wall surface of the communication hole. When the small end includes a distal end of the connecting rod defining a top, the opposite edges are located between the top and the opening in the bottom surface of the oil storage groove.

A small end of a connecting rod includes an oil supply hole extending from an outer surface to an inner surface of the small end. The oil supply hole includes an oil storage groove and a communication hole. The oil storage groove is recessed from the outer surface and extends along the circumference of the small end. The communication hole extends through a bottom surface of the oil storage groove and connects the outer and inner surfaces. Opposite edges of the oil storage groove contact the outer surface in a direction the oil storage groove extends. The bottom surface of the oil storage groove has an opening contacting a wall surface of the communication hole. When the small end includes a distal end of the connecting rod defining a top, the opposite edges are located between the top and the opening in the bottom surface of the oil storage groove.

The bearing apparatus 1 includes a crankshaft having multiple journals, main bearings supporting the crankshaft, and a bearing housing. The plurality of journals include a first journal with a lubricating oil passage and a second journal without a lubricating oil passage. The first and second journals are supported by first and second main bearings, respectively. The bearing housing is constituted by an Al-alloy upper housing and an Fe-alloy lower housing. The depth of the oil groove of the upper half bearing of the second main bearing at least in a ±45° region is equal to or smaller than a half of the depth of the oil groove of the upper half bearing of the first main bearing in the ±45° region.

An engine cylinder block includes a control valve and stratified layers defining a network internal to the cylinder block. The network includes a main feed line in fluid communication with the control valve, and branched and winding arterial channels extending from the main feed line with diameters that taper to define nozzles configured to spray coolant on sides of pistons carried within the cylinder block.

A supply pump includes a housing that has a tappet receiving chamber, which receives a plunger drive mechanism, and oil for lubricating respective lubricating portions of the plunger drive mechanism is temporarily retained in the tappet receiving chamber. In the housing, a communication hole opens in an inner peripheral wall surface of a tappet guide and guides the oil from a tappet upper side chamber into a tappet lower side chamber at the time of upwardly moving a tappet.

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.

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 bearing structure has a crankshaft rotatably supported by a crankshaft bearing part, formed of a cylinder block of an internal combustion engine and a first bearing cap, through a bearing metal, a second shaft rotatably supported by a second shaft bearing part formed of the first bearing cap and a second bearing cap, wherein the bearing metal has a bearing metal planar portion for rotatably supporting the crankshaft with an entire inner peripheral surface of the bearing metal, the inner peripheral surface at which the bearing metal planar portion is formed, a bearing metal oil groove portion formed with an oil groove formed to extend circumferentially in an inner peripheral surface of the bearing metal, the inner peripheral surface at which the bearing metal oil groove portion is formed, a first oil hole opening at the oil groove, and a second oil hole opening at the oil groove.