Patent ID: 8393433

Claim:
An exhaust structure of a motorcycle, in which a main tube is provided for extending rearwardly from a head pipe disposed at a front side of a main body, an engine is disposed under the main tube, the engine includes a cylinder extending upwardly from a crankcase, a down tube is disposed on a center line in a left-right direction of the main body, a lower frame extending downwardly from the down tube and having left and right side lower frames which are parallel to each other and which extend rearwardly under the engine, the exhaust structure comprising: an exhaust port open at a front side of the cylinder, the exhaust port being disposed behind the down tube and being deviatingly open at a right side from the center line in the left-right direction of the main body, a first exhaust pipe connected to the exhaust port and extending downwardly and forwardly at an angle to the right side of the main body; a first expansion chamber directly connected to a downstream end of the first exhaust pipe; a second expansion pipe directly connected to a downstream end of the first exhaust chamber via a joint, the joint being at a position directly above a clutch storage portion protruding to the right side in the crankcase and near a lower portion of a throttle body, and a muffler having a second expansion chamber directly connected to a downstream end of the second exhaust pipe, wherein the first exhaust pipe includes at least first, second, third, and fourth bending portions, the first exhaust pipe connected to the exhaust port bends and extends down toward a left side of the main body at the first bending portion in front of the down tube, and then the first exhaust pipe bends along a curve of the lower frame at the second bending portion at a front side of the lower frame at the left side of the main body, and then the first exhaust pipe extends rearwardly and thereafter extends to the front side of the main body while being bent at the third bending portion to an inside of the main body, and then the first exhaust pipe bends to an upper one side of the main body at the fourth bending portion under the first bending portion, and is connected to the first expansion chamber, wherein the third bending portion has a U-shape, is arranged on the center line in the left-right direction of the main body, and opens toward the front of the motorcycle, and portions of the first exhaust pipe extending forwardly from left and right sides of the U-shaped third bending portion are arranged between and are substantially parallel to portions of the left and right side lower frames extending rearwardly under the engine, and when the first expansion chamber is viewed in side view, an upper-most portion of the first expansion chamber can be seen to be disposed entirely below where a head cover is attached to a cylinder head of the engine, wherein the first expansion chamber has an inner sidewall facing the cylinder head and the exhaust port, and at least a portion of the inner side wall facing the cylinder head is substantially flat.