Chain roller tensioner ensures proper tension and alignment of the chain. It can prevent the chain from derailing, excessive wear of the sprocket and prolong the life of the chain. If the chain is not properly tensioned, it will be lost or broken. Eventually the side cover and stator plate will be damaged.Chain tensioner spring loaded compatible for 49cc 66cc 80cc Engine Motorized Bike.Simple installation steps: STEP 1: It is easier to connect one side of the spring to the curved side of the mounting plate, this side has 2 small holes (the top hole has greater tension than the bottom hole). : In the tensioner Among the 5 screws/bolts, 2 lock nuts and 2 washers included in the kit, use only small screws/bolts and lock nuts to connect the tensioner arm to the mounting plate.Step 3: Remove the old screws from the housing cover, place the tension plate on the housing cover, then use 3 identical screws to install the tension plate on the top of the housing cover and tighten the new screws.Step 4: Take the largest screw/bolt and add a washer, then the chain tensioner, then another washer, and then lock the nut to any of the 4 large holes on the tensioner arm (make sure two Washer on the side) Step 5: Connect the spring from the tensioner plate to the tensioner arm.Material:Metalcolour:blackPackage Contents:1 x Chain Tensioner SetOnly the above package content, other products are not included.Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.