The single timing chain setup was standard on early Mini & Mini Cooper. The single chain system had as standard a pair of rubber rings around the outside edge of the gear to act as a tensioner for the chain. This is the later gear as used on the A+ Mini engines which used a separate chain tensioner. It can be used in place of the original gear. Optionally, just add new rings to your old gear (see part 8G549), or choose the better option and upgrade to the duplex set up (C-AJJ3323).