Abstract: A guide member for a valve actuation mechanism, the guide member having a slot or profiled surface defining a valve actuating portion and a non-valve actuating portion. A valve actuating member such as a pin, moves along the slot or profiled surface in a cyclic fashion, wherein the pin is connected to a valve so that when the pin moves along the valve actuating portion, the valve is actuated, and when the pin moves along the non-valve actuating portion, the valve is not actuated. The non-valve actuating portion of the slot or profiled surface is of sufficient length such that the entire range of cyclic motion of the pin is able to be contained within the non-valve actuating portion. To move the range of cyclic motion from one section of the guide path to another, the guide member may be moved relative to the pin. Said arrangement allows a valve to be selectively operated or deactivated without changing the cyclic motion of the pin, but by merely moving the guide member.