The Yamaha YZM500 was the best known aluminium-framed race bike. It also had the distinction of being the only water-cooled, open class, two-stroke bike. The YZM500 only raced for two years (1987-1988) by riders Leif Persson, Kurt Ljungqvist and Jacky Vimond. There were also a coupled used for beach races. Only eight complete YZM500s were ever made, six in 1987 and two more for the 1988 season.
References
Yamaha YZM500 Wikipedia(Text) CC BY-SA