A cast-aluminum engine block for a compression-ignition internal combustion engine includes a plurality of cylinders that are disposed in an in-line arrangement. The engine block includes a top portion including a top deck and a bottom portion including a plurality of main bearings that are disposed to support journals of a crankshaft. An integrated flow channel is formed between the second end and the last cylinder and proximal to the top deck, and is a continuous channel that passes from the first side to the second side through the portion of the engine block between the second end and the last cylinder and proximal to the top deck. A coolant passageway is disposed in the engine block between the integrated flow channel and the last cylinder, and is oriented parallel to the elevation axis.

An improved air-cooled aviation engine includes a compact combustion chamber having an intake valve opening, an exhaust valve opening, and a generally elliptical shape. The elliptical shape has a major axis and a minor axis, with the major axis intersecting both the intake valve opening and the exhaust valve opening. In some examples, the major axis is the same length or shorter than a diameter of a cylinder bore of the engine, and the minor axis is smaller than the major axis. Combustion is thus constrained to a smaller area than that of the cylinder bore.

An improved air-cooled aviation engine includes a compact combustion chamber having an intake valve opening, an exhaust valve opening, and a generally elliptical shape. The elliptical shape has a major axis and a minor axis, with the major axis intersecting both the intake valve opening and the exhaust valve opening. In some examples, the major axis is the same length or shorter than a diameter of a cylinder bore of the engine, and the minor axis is smaller than the major axis. Combustion is thus constrained to a smaller area than that of the cylinder bore.

An air/oil-cooled internal combustion engine capable of increasing accuracy in detection of the temperature of the air/oil-cooled internal combustion engine by a temperature sensor and carrying out the warm-up operation after the start-up of the air/oil-cooled internal combustion engine favorably. The air/oil-cooled internal combustion engine includes cooling fins that are provided on the circumferences of a cylinder block and a cylinder head; and a cooling passage that is provided in a combustion chamber upper wall covering a combustion chamber of the cylinder head and is used for cooling the combustion chamber upper wall with lubrication oil. The air/oil-cooled internal combustion engine has a temperature sensor configured to detect the temperature of the air/oil-cooled internal combustion engine by detecting the temperature of oil. The temperature sensor faces a cooling oil outlet portion of the cooling passage.

An air/oil-cooled internal combustion engine capable of increasing accuracy in detection of the temperature of the air/oil-cooled internal combustion engine by a temperature sensor and carrying out the warm-up operation after the start-up of the air/oil-cooled internal combustion engine favorably. The air/oil-cooled internal combustion engine includes cooling fins that are provided on the circumferences of a cylinder block and a cylinder head; and a cooling passage that is provided in a combustion chamber upper wall covering a combustion chamber of the cylinder head and is used for cooling the combustion chamber upper wall with lubrication oil. The air/oil-cooled internal combustion engine has a temperature sensor configured to detect the temperature of the air/oil-cooled internal combustion engine by detecting the temperature of oil. The temperature sensor faces a cooling oil outlet portion of the cooling passage.

A small air-cooled internal combustion engine includes an aluminum cylinder block, an aluminum cylinder head welded to the aluminum cylinder block, and a weld securing the aluminum cylinder block to the aluminum cylinder head, wherein a joint having a first length is formed between the aluminum cylinder block and the aluminum cylinder head and wherein the weld extends for a second length that is at least 25% of the first length.

A small air-cooled internal combustion engine includes an aluminum cylinder block, an aluminum cylinder head welded to the aluminum cylinder block, and a weld securing the aluminum cylinder block to the aluminum cylinder head, wherein a joint having a first length is formed between the aluminum cylinder block and the aluminum cylinder head and wherein the weld extends for a second length that is at least 25% of the first length.

In a cylinder head cooling structure of engine E including a camshaft 15 rotated by a crankshaft 2, a push rod, and an actuatable rocker arm, an injection hole 46 for injecting oil pressurized by an oil pump 44 is formed in a shaft portion 43 between an exhaust cam 36 on the camshaft 15 and a journal 15j at its rear end, and the oil injected the injection hole 46 is allowed to enter a rear cylinder head cover 7 through a pushrod chamber in which the push rod is disposed.

A small air-cooled internal combustion engine includes an aluminum cylinder block, an aluminum cylinder head welded to the aluminum cylinder block, and a weld securing the aluminum cylinder block to the aluminum cylinder head, wherein a joint having a first length is formed between the aluminum cylinder block and the aluminum cylinder head and wherein the weld extends for a second length that is at least 25% of the first length.

A small air-cooled internal combustion engine includes an aluminum cylinder block, an aluminum cylinder head welded to the aluminum cylinder block, and a weld securing the aluminum cylinder block to the aluminum cylinder head, wherein a joint having a first length is formed between the aluminum cylinder block and the aluminum cylinder head and wherein the weld extends for a second length that is at least 25% of the first length.