I've had some success constraining the link axis to each other and also to an assembly sketch whose shape mimics the "pitch dia shape" of the finished assy.
The driven distance between the one plane (spocket center point location) and a parellel plane for the tightening roller is kept by an equation which keeps the length of one link times the # of links = the overall length of the assembly sketch constant.
Remember...
"If you don't use your head,
your going to have to use your feet."