In an internal combustion engine, an oil return passage extending from a breather chamber can be formed without increasing the number of component parts and without increasing the size of the internal combustion engine. The internal combustion engine (1) comprises an engine block (30) defining a cylinder (2); a case member (19) fastened to a lower part of the engine block to define a crank chamber jointly with the engine block; a bearing member (50) fastened to the engine block in the crank chamber to rotatably support a crankshaft; a breather chamber (113) defined in the engine block; an inlet passage (112) formed in the engine block to communicate the crank chamber with the breather chamber; a connection pipe (114) communicating the breather chamber with an intake device; and an oil return passage (150) formed at least in the bearing member, and extending from a bottom part of the breather chamber to an oil return port (147) opening at an outer surface of the bearing member. The oil return port may be provided in a lower part of the bearing member.

Methods for making an apparatus comprising a cylinder for an engine having at least one combustion chamber and a squish area disposed at or around a base of the at least one combustion chamber, wherein the at least one combustion chamber comprises a paraboloidal cavity.

The overhead camshaft engine (10) includes a cylinder block (11), a crankcase (12) attached to a lower part of the cylinder block to define a crankcase chamber (32), a bearing retaining member (60) attached to a part of the cylinder block, a crankshaft (20) rotatably supported by a pair of bearings (21, 22) supported by the cylinder block and the bearing retaining member, respectively, and a crankshaft pulley (53) attached to a part of the end of the crankshaft projecting outward from the bearing supported by the bearing retaining member.

In an overhead cam engine (10) having a first bearing (21) supported by the cylinder block (11), and a second bearing (22) supported by a bearing retaining member (60) attached to the cylinder block inside a crankcase chamber (12) for rotatably supporting a crankshaft (20), the crankshaft is provided with a reduced diameter portion (24b) having a smaller outer diameter than an adjoining part of the crankshaft on a side of the second bearing facing away from a cylinder (15) defined in the cylinder block, and a crankshaft pulley (53) is mounted on the reduced diameter portion.

An engine (E) includes a crankcase body (19) including a bottom plate (19a) and a tubular portion (19c), a crankcase cover (20) covering a case opening portion (19b) of the crankcase body (19), a crankshaft (2), a cylinder base portion (21a) located inside the crankcase body (19), a cylinder block (21b) located outside the crankcase body (19), and a camshaft (25) located inside the crankcase body (19) and between the bottom plate (19a) and cylinder base portion (21a). The crankcase body (19) has the bottom plate (19a) detachably attached to the tubular portion (19c).

In an internal combustion engine, an oil return passage extending from a breather chamber can be formed without increasing the number of component parts and without increasing the size of the internal combustion engine. The internal combustion engine (1) comprises an engine block (30) defining a cylinder (2); a case member (19) fastened to a lower part of the engine block to define a crank chamber jointly with the engine block; a bearing member (50) fastened to the engine block in the crank chamber to rotatably support a crankshaft; a breather chamber (113) defined in the engine block; an inlet passage (112) formed in the engine block to communicate the crank chamber with the breather chamber; a connection pipe (114) communicating the breather chamber with an intake device; and an oil return passage (150) formed at least in the bearing member, and extending from a bottom part of the breather chamber to an oil return port (147) opening at an outer surface of the bearing member. The oil return port may be provided in a lower part of the bearing member.

An engine (E) includes a crankcase body (19), a crankcase cover (20) covering a case opening portion (19b) of the crankcase body (19), a crankshaft (2), a cylinder base portion 21a located inside the crankcase body (19), a cylinder block (21b) located outside the crankcase body (19). The crankcase cover (20) is detachably attached to an upper portion of the crankcase body (19).

Methods for making an apparatus comprising a cylinder for an engine having at least one combustion chamber and a squish area disposed at or around a base of the at least one combustion chamber, wherein the at least one combustion chamber comprises a paraboloidal cavity.

In an internal combustion engine, a breather chamber can be formed without increasing the number of component parts. The internal combustion engine (1) comprises an engine block (30) defining a cylinder (2); a case member (19) fastened to a lower part of the engine block to define a crank chamber (4) jointly with the engine block; and a bearing member (50) fastened to the engine block in the crank chamber to rotatably support a crankshaft; wherein the engine block is provided with a central recess (134) formed in a part thereof to which the bearing member is fastened, a blow-by gas inlet passage (112, 116, 121) communicating the central recess with the crank chamber, and a blow-by gas return passage (122, 118) forming a part of a passage communicating the central recess with an intake device, the central recess and the bearing member jointly defining a central breather chamber.

A cylinder structure of an internal combustion engine contains: a body, two lids, and multiple positioning elements. The body has a combustion chamber, an air inlet, an air outlet, and two scavenging units. A respective scavenging unit has a first scavenging orifice, a second scavenging orifice, a first fringe, a second fringe, a first engagement portion, and a first fixing orifice. The two lids are configured to close the first scavenging orifice and the second scavenging orifice, an air conduit is defined between a respective lid and an external fence of the body, and the respective lid has multiple second fixing orifices. A respective positioning element has a stem and at least one hook, the stem extends into the first engagement portion, and the stem is rotated so that the at least one hook contacts with the respective lid, and the respective lid is connected with the body.