Abstract: An engine valve actuating apparatus includes a housing that contains an activation piston bore and an actuation piston bore. The activation piston is disposed in the activation piston bore and configured to actuate an engine valve. The actuation piston includes at least one side surface that is in sliding contact with the inner surface of the actuation piston bore so that the actuation piston can slide within the actuation piston bore. The actuation piston also has a guide mechanism, which guides the first and second links to move in a plane between the first position and the second position. At least a part of the guide mechanism is below at least a part of the at least one side surface of the actuation piston.