A cover covering an engine and an intake duct for introducing fresh air outside an engine room into a combustion chamber of the engine are provided in the engine room. The cover includes a top face cover portion covering the engine from above, and a side face cover portion covering the engine from the lateral side. The intake duct is disposed so as to be continuous to a side edge of the side face cover portion such that the intake duct covers the engine from the lateral side together with the side face cover portion.

A quantitative one-way oil gas lubricant system and a method for a 4-stroke engine, including a preceding stage quantitative oil intake orifice that is connected to a lubricant case on a wall of a crankcase of the 4-stroke engine, and a final stage quantitative airflow orifice disposed at a cylinder cover of the 4-stroke engine, are provided. A diameter of the preceding stage quantitative oil intake orifice D.sub.1 and a diameter of the final stage quantitative airflow orifice satisfy an equation: D.sub.1/D.sub.3=0.8-1.5, wherein a one-way connected oil gas lubricant channel is disposed between the preceding stage quantitative oil intake orifice and the final stage quantitative airflow orifice. A lubricant oil sucked from the preceding quantitative oil intake orifice by the crankcase flows along the oil gas lubricant channel and lubricates the engine parts that the channel passes through in turns. Finally, a minute quantity of waste oil gas that flows out from the final stage quantitative airflow orifice is introduced into a cylinder of the 4-stroke engine and is to be burned completely. The supply quantity of the lubricant oil may be controlled, and no extra lubricant oil gas may flow out from the final stage quantitative airflow orifice, therefore, the quantitative and one-way lubricating is realized.

An engine block includes one or more cylinder bores wherein each cylinder bore is surrounded by a cylinder bore wall. The cylinder bore wall includes a liner stop mechanism to locate a liner in the cylinder bore. The cylinder bore includes a mid-portion that spans between an upper end and a lower end, wherein the liner stop mechanism can be located near the upper end, near the lower end, or the mid-portion. The engine block has an outer cylinder block wall that is exterior to the cylinder bore wall. The outer cylinder block wall includes a first rib positioned above the liner stop mechanism and a second rib positioned below the liner stop mechanism relative to a cylindrical axis of the cylinder bore. The first and second ribs straddle the liner stop mechanism to reduce rotation and buckling of the liner during operation of the engine.

Provided is an engine device that can enlarge a space inside a case without lowering support stiffness. An engine (2) is attached to a case (11) via support parts (81, 82). A rear lower portion support part (82), which is one of the support parts, includes an attachment rib (11b) as a mounting part provided in the case (11) and an attachment bracket (91) fastened to a bottom of a crankcase (46) by a fastening bolt (90) and attached to the attachment rib (11b). The fastening bolt (90) penetrates through a through hole (92a) provided in the attachment bracket (91) and is screwed into a screw hole (46e) formed obliquely inward at a corner of the bottom of the crankcase (46).

An engine block includes one or more cylinder bores at least partially surrounded by a cylinder bore wall. The cylinder bore wall includes a liner stop mechanism to support a liner in the cylinder bore. The engine block has an outer cylinder block wall that is exterior to the cylinder bore wall. The outer cylinder block wall includes at least one rib located relative to the liner stop mechanism to reduce rotation and buckling of the liner during operation of the engine.

A head cover structure (45) for an internal combustion engine (1) comprises a head cover (4) connected to a cylinder head (3), and an auxiliary cover (44) connected to the head cover and defining a gas-liquid separation passage (74) jointly with the head cover, the gas-liquid separation passage being communicated with a crankcase chamber (11) of the internal combustion engine, and configured to separate lubricating oil from a crankcase gas drawn from the crankcase chamber, wherein the auxiliary cover is integrally formed with an intake pipe (49) internally defining a part of an intake passage (20) of the internal combustion engine, and the auxiliary cover internally defines a crankcase gas introduction passage (63) communicating the gas-liquid separation passage with an interior of the intake pipe.

A crank cap assembly including a single crank cap rotatably supporting a crankshaft includes: a fastening member fastened to the crank cap, a mass member; and an elastic rubber member elastically attaching the mass member to the crank cap. The elastic rubber member includes a first rubber part arranged between the fastening member and the mass member and a second rubber part arranged between the crank cap and the mass member. The first rubber part and the second rubber part are arranged to be aligned in the mounting direction when attaching the crank cap to an engine body, and the elastic rubber member is formed so that a length in the mounting direction is longer than a maximum length in a cross-section of the elastic rubber member perpendicular to the mounting direction.

An engine is provided with: an engine body; and a top cover that covers the engine body, wherein at least a pair of engaging claws are provided to lateral walls, on both sides, of the top cover so as to extend downward, and a pair of engaging holes with which the engaging claws engage are provided to the engine body side. Each of the engaging claws is provided with a plate section that is provided so as to extend downward, and a bulging section that is provided to the leading end of the plate section and that bulges inward from the plate section, and the bulging section engages with the bottom surface of an inner wall section of the corresponding engaging hole.

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 head cover structure (45) for an internal combustion engine (1) comprises a head cover (4) connected to a cylinder head (3), and an auxiliary cover (44) connected to the head cover and defining a gas-liquid separation passage (74) jointly with the head cover, the gas-liquid separation passage being communicated with a crankcase chamber (11) of the internal combustion engine, and configured to separate lubricating oil from a crankcase gas drawn from the crankcase chamber, wherein the auxiliary cover is integrally formed with an intake pipe (49) internally defining a part of an intake passage (20) of the internal combustion engine, and the auxiliary cover internally defines a crankcase gas introduction passage (63) communicating the gas-liquid separation passage with an interior of the intake pipe.