An engine has a cylinder block formed by a block material and defining at least one cylinder. The block defines a lubrication circuit with fluid passages including an inlet passage, a main oil gallery, a crankshaft bearing lubrication passage, and a piston ring lubrication passage. The fluid passages are formed by continuous metal walls in contact with and surrounded by the block material. At least one of the fluid passages is curved. A method of forming a component with an internal pressurized lubrication circuit includes positioning a lost core insert in a tool, with the insert shaped to form a lubrication circuit. The lost core insert has a lost core material generally encapsulated in a continuous metal shell, and at least one curved section. Material is provided into the tool to form a body surrounding the lost core insert thereby forming a component preform.

A combination of a cylinder 62 of an internal combustion engine and a piston ring 40 for sliding an inner periphery of the cylinder, wherein at least a sliding face of the cylinder is composed of an aluminum alloy including 8 mass % to 22 mass % of Si and at least one or more particles selected from the group consisting of Si, Al.sub.2O.sub.3 and SiO.sub.2 particles each having a diameter of 3 m or more, and at least an outer periphery of the piston ring is coated with a hard carbon coating 14 composed only of hydrogen and carbon.

Provided is a cylinder liner which can reduce the friction of the sliding surface from conventional levels and improve fuel efficiency without increasing oil consumption from conventional levels. When the inner circumferential surface of a cylinder liner or cylinder bore used in an internal combustion engine has a first sliding region, a second sliding region, and a third sliding region, and when respective surface roughness Rvk is from 0.05 ?m to 0.3 ?m, from 0.4 ?m to 1.5 ?m, and from 0.15 ?m to 0.7 ?m, a friction can be reduced while maintaining oil consumption.

Provided is a cylinder liner which can reduce the friction of the sliding surface from conventional levels and improve fuel efficiency without increasing oil consumption from conventional levels. When the inner circumferential surface of a cylinder liner or cylinder bore used in an internal combustion engine has a first sliding region, a second sliding region, and a third sliding region, and when respective surface roughness Rvk is from 0.05 ?m to 0.3 ?m, from 0.4 ?m to 1.5 ?m, and from 0.15 ?m to 0.7 ?m, a friction can be reduced while maintaining oil consumption.

To provide a piston ring free from microwelding to a piston while exhibiting excellent wear resistance in side surfaces, for a long period of use in a high-temperature, high-pressure environment, and its production method, a nitride layer is formed on at least one of upper and lower side surfaces of the piston ring, and then subjected to a phosphate chemical conversion treatment, such that the nitride layer has at least one of granular and vermicular surface forms.

An internal combustion engine is provided with one or more oil drain-back passages. The oil drain-back passage include an entrance into a crankcase via a crankcase breathing window, the crankcase breathing window disposed within and through a bulkhead wall of the crankcase. Thus, each oil drain-back passage may be routed from a cylinder head of the engine to a crankcase breathing window where oil may then enter the crankcase and flow downward into an oil pan coupled to the crankcase.

An internal combustion engine is provided with one or more oil drain-back passages. The oil drain-back passage include an entrance into a crankcase via a crankcase breathing window, the crankcase breathing window disposed within and through a bulkhead wall of the crankcase. Thus, each oil drain-back passage may be routed from a cylinder head of the engine to a crankcase breathing window where oil may then enter the crankcase and flow downward into an oil pan coupled to the crankcase.

A method is proposed for producing a cylinder working surface of an internal combustion engine that is optimized in terms of friction and wear.

A cylinder bore for a cylinder housing of an internal combustion engine may have a cylinder running surface, an upper reversal point and a lower reversal point at which a piston, which may be moved up and down in the cylinder bore and may have piston rings and a piston skirt, may reach a speed which approaches zero during engine operation. The cylinder bore may also have a region between the upper reversal point and the lower reversal point at which the piston may reach a maximum speed during engine operation. The cylinder bore may further have at least two circumferential depressions formed within the region, the at least two circumferential depressions each having a diameter that may be greater than a diameter of the cylinder bore above the region and below the region.

A cylinder bore for a cylinder housing of an internal combustion engine may have a cylinder running surface, an upper reversal point and a lower reversal point at which a piston, which may be moved up and down in the cylinder bore and may have piston rings and a piston skirt, may reach a speed which approaches zero during engine operation. The cylinder bore may also have a region between the upper reversal point and the lower reversal point at which the piston may reach a maximum speed during engine operation. The cylinder bore may further have at least two circumferential depressions formed within the region, the at least two circumferential depressions each having a diameter that may be greater than a diameter of the cylinder bore above the region and below the region.