A micro-engine including a rotation structure, the rotation structure including a head portion, a rear portion, and a deformable portion connecting both portions. The deformable portion is deformable in elongation or compression along a main axis and includes a spring element displaying a free end. The free end of the spring element includes at least an abutment member. The deformable portion further includes a wheel-platform which displays a first and a second face, being configured to cooperate with the free end of the spring element in order to transform a back-and-forth movement of the at least one spring element into a rotational movement of the wheel-platform.

A power transmission apparatus includes a shift drum, a clutch, a clutch lifter, and a transmission body. The shift drum makes a dowel be extracted/inserted between a shifter and a shift gear. The clutch has first friction plates and second friction plates. The first friction plates rotate around a main shaft by receiving power from a crankshaft. The second friction plates are disposed alternately with the first friction plates and are relatively non-rotatably supported by the main shaft. The clutch lifter is displaced between a connection position at which power is transmitted by the clutch and a disconnection position at which the transmission of the power is disconnected. The transmission body transmits a driving force to the shift drum while the clutch lifter moves from the connection position to the disconnection position, in accordance with rotation of a shift spindle that rotates in accordance with a driving force.

A power transmission apparatus includes a shift drum, a clutch, a clutch lifter, and a transmission body. The shift drum makes a dowel be extracted/inserted between a shifter and a shift gear. The clutch has first friction plates and second friction plates. The first friction plates rotate around a main shaft by receiving power from a crankshaft. The second friction plates are disposed alternately with the first friction plates and are relatively non-rotatably supported by the main shaft. The clutch lifter is displaced between a connection position at which power is transmitted by the clutch and a disconnection position at which the transmission of the power is disconnected. The transmission body transmits a driving force to the shift drum while the clutch lifter moves from the connection position to the disconnection position, in accordance with rotation of a shift spindle that rotates in accordance with a driving force.

A micro-engine including a rotation structure, the rotation structure including a head portion, a rear portion, and a deformable portion connecting both portions. The deformable portion is deformable in elongation or compression along a main axis and includes a spring element displaying a free end. The free end of the spring element includes at least an abutment member. The deformable portion further includes a wheel-platform which displays a first and a second face, being configured to cooperate with the free end of the spring element in order to transform a back-and-forth movement of the at least one spring element into a rotational movement of the wheel-platform.