To stop actuation of the valves, the link between the valve and the camshaft is interrupted. To achieve this, the one-piece roller-type rocker arm is replaced by two special arms on each cylinder, which are referred to by engine development engineers as the primary and secondary arms. The role of the primary arm is valve control, while the secondary arm follows the cam lift. When the engine is in eight-cylinder mode, the two arms are linked by a locking piston. Automatic cylinder cut-out breaks this link hydraulically by forcing the locking pistons against special return springs by means of electromagnetic shift valves. Valve actuation on that cylinder then ceases. To reactivate the cylinders, the hydraulic pressure acting on the pistons is released, via electromagnetic shift valves, and the springs return them to their original position, where the primary and secondary arms are locked.