Cam belt tensioner peugeot 206 1.9 diesel?

Hi,remove wheel and plastic cover under wheel arch,the tensioner will be the small plastic one between the large pulleys at the bottom it should have a allen key bolt holding it tight.It untightens anti clockwise and as you turn it with the allen key you will see it slacken,unless it's already to slack,but when tightening you will see it move and the belt tighten as you move it,then whilst keeping it in postion tighten the allen key back up again,I think it's an 8mm allen key.