Hi Do not try to take off the rear idler as shown in the photo above it dosnt come off like that ,if you need to remove the rear idler there are 3 screws on the inside face of the idler ,there not easy to get at ,you have to get them by turning the tank upside down and get them from under neath ,once you have undone these the idler splits and there is a screw holding the other part to the tank..
 
   The sprocket take the hub cover off ,take a close look there is a place for a small flat screwdriver to filp it out ,once removed there is an allen screw to remove to take the sprocket off.

 regards pete