To adjust the front chain, loosen the two nuts holding gearbox on to frame and turn nut provided which is on top of the gearbox stays and behind the gearbox itself.
There should be from ½" to ¾" up and down movement in this chain. It should be tried all round and set so that it is a little slack in its tightest place. After the adjustment tighten up the nuts. The adjusting nut should also be turned so that it pushes the gearbox towards the engine after clamping up tight. This prevents any possibility of the box slipping back due to the stronger pull of the back chain.