US Patent 7562597 Engine for motorcycle

An engine for a motorcycle includes an engine case, a crankshaft rotatably supported within the engine case and extending laterally, an intermediate shaft being substantially parallel to the crankshaft and being rotated by the crankshaft at the same speed via a primary drive gear and a primary driven gear, a transmission input shaft being substantially parallel to the intermediate shaft and being rotated by the intermediate shaft at reduced speed via a secondary drive gear and a secondary driven gear, a transmission output shaft being substantially parallel to the transmission input shaft and being rotated by the transmission input shaft at changed speed via any combination of a plurality of transmission drive gears and transmission driven gears, and a clutch unit disposed on the intermediate shaft and capable of transmitting and interrupting rotation of the intermediate shaft to the transmission input shaft.