This method of adjusting rockers will guarantee that the cam lobe of the cylinder that is being adjusted is at its lowest point.
With the piston at TDC, with both valves in the closed position, do the following:
The first thing you want to do is verify zero valve lash. The best way to do this is to wiggle the push rod up & down as you tighten the rocker arm nut. At the point where the push rod no longer moves up & down, That is zero lash. You now have a starting point for verifying “true” zero lash & the lifter pre-load.
When you adjust the valves you are setting the lifter pre-load, Pre-load is the amount of distance the push rod seat (or “cup”) moves away from the retaining clip.
To set true zero lash & the lifter pre-load, We are going to follow the “EO / IC” procedure.
What is “EO / IC?
EO, is Exhaust Opening; IC, is Intake Closing.
We have the piston at TDC (Both valves are in the closed position), Rotate the engine in the normal direction of rotation (clockwise, if you are facing the front of the engine).
You will see the exhaust valve just starting to open, stop rotating the engine & back off the intake rocker arm.(You are going to back off the rocker arm & re-verify for true zero lash, As you are now positively on the base circle of the camshaft whereas the previous lash adjustment was just a pretty close ballpark guess.) You will once again wiggle the push rod up & down as you tighten the rocker arm nut. When all up & down movement is gone, tighten the rocker arm nut ½ turn, tighten the hex head set screw until it bottoms out on the rocker stud, tighten the rocker arm nut ¼ additional turn. You have now set the lifter pre-load at .045”.
Rotate the engine, You will see the exhaust valve fully open & then close. Watching the intake valve that you just set, You will see it open, You want to keep rotating the engine until it fully opens & then starts to close. When it is almost closed, stop rotating the engine. Set the exhaust valve the same way you did the intake valve.