A linear reciprocating engine may include a cylinder having a first combustion chamber at one end and a second combustion chamber at an opposing end, first and second cylinder heads located at an end of the first and second combustion chambers, respectively, and a double-faced piston slidably mounted within the cylinder. The engine may further include a first piston rod portion extending from a first face of the double-faced piston through the first combustion chamber, and a second piston rod portion extending from a second face of the piston through the second combustion chamber. Passageways in the piston rod portions may be configured to communicate gases between the combustion chamber and a location outside the cylinder and configured to prevent gases from being exchanged between the cylinder and a location outside the cylinder via a path that crosses both face of the piston.

A linear reciprocating engine may include a cylinder having a first combustion chamber at one end and a second combustion chamber at an opposing end, first and second cylinder heads located at an end of the first and second combustion chambers, respectively, and a double-faced piston slidably mounted within the cylinder. The engine may further include a first piston rod portion extending from a first face of the double-faced piston through the first combustion chamber, and a second piston rod portion extending from a second face of the piston through the second combustion chamber. Passageways in the piston rod portions may be configured to communicate gases between the combustion chamber and a location outside the cylinder and configured to prevent gases from being exchanged between the cylinder and a location outside the cylinder via a path that crosses both face of the piston.

A motor engine having an oxygen sensor is provided, including: a cylinder head, including a main body and a protruding tube protruding outwardly from the main body, the main body including a first end portion, a second end, and a combustion chamber, the protruding tube having a protrusive receptacle protruding outwardly therefrom, the main body defining an axial direction; an exhaust passage, communicated with the combustion chamber and the protruding tube; an oxygen sensor, inserted into the protrusive receptacle, including a sensing portion which is inserted into the exhaust passage; wherein as viewed in a lateral direction of the cylinder head, two surfaces of the main body along the axial direction disposed on two opposite sides defines two boundary lines, the oxygen sensor and the main body are in an overlapping arrangement and does not protrude out of the two boundary lines.

A motor engine having an oxygen sensor is provided, including: a cylinder head, including a main body and a protruding tube protruding outwardly from the main body, the main body including a first end portion, a second end, and a combustion chamber, the protruding tube having a protrusive receptacle protruding outwardly therefrom, the main body defining an axial direction; an exhaust passage, communicated with the combustion chamber and the protruding tube; an oxygen sensor, inserted into the protrusive receptacle, including a sensing portion which is inserted into the exhaust passage; wherein as viewed in a lateral direction of the cylinder head, two surfaces of the main body along the axial direction disposed on two opposite sides defines two boundary lines, the oxygen sensor and the main body are in an overlapping arrangement and does not protrude out of the two boundary lines.

A piston is provided for an internal combustion engine. The piston may include a cylindrical first piston portion having a first diameter, a cylindrical second piston portion of the first diameter, and a cylindrical third piston portion of a second diameter less than the first diameter located between the first piston portion and the second piston portion. The first piston portion may be configured such that prior to assembly, the first piston portion is separate from the second piston portion. The piston may also include a continuous, gapless piston ring circumscribing the third piston portion, where the piston ring may be configured such that when heated the piston ring deforms in an axial direction of the piston.

A piston is provided for an internal combustion engine. The piston may include a cylindrical first piston portion having a first diameter, a cylindrical second piston portion of the first diameter, and a cylindrical third piston portion of a second diameter less than the first diameter located between the first piston portion and the second piston portion. The first piston portion may be configured such that prior to assembly, the first piston portion is separate from the second piston portion. The piston may also include a continuous, gapless piston ring circumscribing the third piston portion, where the piston ring may be configured such that when heated the piston ring deforms in an axial direction of the piston.

An engine includes a crankcase with cylinders and fins on outer circumferences of the cylinders. A crank shaft penetrates the crankcase. A cooling fan is provided on an outer side of the crankcase and arranged coaxially with the crank shaft. A first cover covers an outer side of the cylinders and the crankcase, and the cooling fan. A second cover capable of being detached from/attached to the first cover. The first cover includes a first opening facing the cooling fan, and second openings facing the fins. The second cover includes an air inlet facing the first opening, and attached to the first cover to cover the first opening and the second openings.

An engine includes a crankcase with cylinders and fins on outer circumferences of the cylinders. A crank shaft penetrates the crankcase. A cooling fan is provided on an outer side of the crankcase and arranged coaxially with the crank shaft. A first cover covers an outer side of the cylinders and the crankcase, and the cooling fan. A second cover capable of being detached from/attached to the first cover. The first cover includes a first opening facing the cooling fan, and second openings facing the fins. The second cover includes an air inlet facing the first opening, and attached to the first cover to cover the first opening and the second openings.

In the vehicle structure for mounting an air-cooled internal combustion engine, a crankcase is supported by a body frame in such a manner that crankcase hanger bosses on the crankcase are joined to the body frame via crankcase hanger plates. A cylinder head has left and right cylinder head hanger seating surfaces formed perpendicular to a left-right horizontal direction by cutting out right and left symmetric areas close to side edges of left and right side faces of the cylinder head along with parts of cooling fins. One ends of left and right cylinder head hanger members are fastened respectively to cylinder head hanger attaching seats on which the left and right cylinder head hanger seating surfaces of the cylinder head are formed. The other ends of the left and right cylinder head hanger members are fastened individually to the body frame. The structure is capable of using an engine body itself to improve stiffness of a body frame without use of any particular reinforcing members.

In the vehicle structure for mounting an air-cooled internal combustion engine, a crankcase is supported by a body frame in such a manner that crankcase hanger bosses on the crankcase are joined to the body frame via crankcase hanger plates. A cylinder head has left and right cylinder head hanger seating surfaces formed perpendicular to a left-right horizontal direction by cutting out right and left symmetric areas close to side edges of left and right side faces of the cylinder head along with parts of cooling fins. One ends of left and right cylinder head hanger members are fastened respectively to cylinder head hanger attaching seats on which the left and right cylinder head hanger seating surfaces of the cylinder head are formed. The other ends of the left and right cylinder head hanger members are fastened individually to the body frame. The structure is capable of using an engine body itself to improve stiffness of a body frame without use of any particular reinforcing members.