A chain tensioning device having a tensioner arm with a hole at a free end and a rotary piston part rotatably supported in the hole and which has two chambers. The rotary piston part also has an offset bolt mounting hole with a mounting bolt fixed into a wall. Oil supply channels introduce hydraulic pressure into one of the channels which introduces hydraulic pressure into one of the chambers which rotates the rotary piston part about the mounting bolt, whereby the free end of the tensioner arm pivots toward the chain about the supported end 20 so that a pressing force acts on the chain.
