The valves inside the combustion chamber of a Ford 5-liter engine let in the fuel/air mixture and let out the exhaust gases. In engines with the camshaft in the bottom of the engine, a rod leading from the camshaft pushes one end of a rocker arm up, which levers the other end of the rocker arm down. The downward motion of the rocker arm forces the valve to open. A spring pushes the valve closed again. It's important to adjust the rocker arms so that they touch the valve stem but don't press down on it.
Remove the valve cover with the wrench by undoing the bolts holding it onto the cylinder head.
Scrape the old gasket material off the valve cover and the cylinder head with the scraper. Clean up any debris that fell on the cylinder head.
Find the adjusting nut on top of the rocker arm. There is only one.
Install oil deflector clips to each rocker arm. Follow the directions on oil deflector clip package. The deflectors keep oil from spraying around the engine while the rocker arm is being adjusted.
Put the transmission in "Park" for an automatic transmission. Manual transmissions should have the gearshift in the "Neutral" position. Start the engine. Allow it to warm up for five minutes and let it idle.
Use the wrench to loosen the adjusting nut on the rocker until the engine makes a clacking sound. Turn the wrench slowly the other way until the noise stops. The rocker arm is in the "Zero Lash" position.
Take a look at the manual for the year of your Ford to determine correct adjustment position. The "Zero Lash" position is perfect for a perfect engine. In real life, the adjusting nut has to be a bit tighter. Most Fords require an additional one quarter to one full turn.
