renault RAPID rockers and tappets Available Here. If you’re a mechanic or serious hobbyist, you might be already be familiar with the functions of these parts. Rockers and tappets are mechanical parts that operate your engine valves: the parts that bring in fuel-air mixtures and let out exhaust. Going into gory detail on the function of these parts would be difficult, due to the fact that the configurations of rockers and tappets are different on nearly every engine design. Suffice it to say that these parts are operated by the camshaft to depress or lift the engine valves in synchronization with the process of internal combustion. Rockers and tappets are essential to the efficiency and power of your engine, so replace them if they’re damaged, broken or worn out.