The rocker ball is the bearing surface the rocker ROCKS on.
New they have grooves in them to retain oil for lubrecating the joint while the rocking is going on.. As they get old the grooves wear out and with the absence of the extra oil the wear increases. As the rockers we are speaking about do NOT have an adjustment available in the rocker itself.. any adjustment is done by taking out the original PUSH RODS and installing slightly longer ones.
What I have done in the past is to take all the sparks out and turn the engine by hand. Measuring the lift at each pushrod indivualy.. this will tell me if one or more camshaft lobes has went away.... Which I fear may be your problem.
A common problem with having a VALVE JOB done is the mechanic takes all the rockers and all the balls out and cleans them and then puts them back together RANDOMLY! This method increases the wear as all the parts that have worn to fit each other are no longer together.. I always keep them paired even if I have to WIRE them together for cleaning.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />