1981 Yamaha XS650 (XS-H)…. The Yamaha XS-650 was first introduced in October of 1969 and was quickly known to have one of the most advanced engines in its class of large parallel twin motorcycles. The engine and gearbox are unit construction with the crankcase being split horizontally for ease of assembly whereas other contemporaries in its class where either split vertically or pre-unit construction meaning separate engine and gearbox. The XS-650 was offered in a Standard configuration or Speci