 Later the Hosk company was acquired by Showa Corporation, and in 1960 Yamaha had bought Showa with Hosk's early design of 650 cc twin.When the Yamaha XS 650 was launched in October 1969 it had one of the most advanced engines in its class of large parallel twin motorcycles.The engine and gearbox are unit construction with the crankcase split horizontally for ease of assembly whereas almost all contemporaries in its class in 1969 are either unit construction with a vertically split crankcase or pre-unit construction with separate engine and gearbox.