Insert a small wire through the air bleed hole in the rocker arm and lightly push the check ball down to check the Valve Lifters for free play. While gently holding the check ball down, you should rock the rocker arm up and down to check for free play, which should be a small amount. If free play is absent, install a new Valve Lifter. Remove the valve cover and the rocker arm shaft components, and remove the Valve Lifter(s) from the rocker arm(s). It is essential to mark each rocker arm and Valve Lifter, and keep them in a partitioned box or something suitable to avoid confusion. Putting in place is taking out.