Not a tradesman but willing to help if I can
Paul Williams posted an answer for this Kymco 2008 Mongoose 250:
"Hi Matt only help I can give is look along top & bottom of chain for a tensioner it..."
Paul Williams posted an answer for this Arctic Cat 2010 550 H1 EFI TRV 4x4:
"Hi jguild45 Look all around at top & sides of motor see if you can find a black round..."