There's a lot to be said for the level of experience of the operator of any machine tool. Today's machinery with a computer controlling every part of the operation has created a couple of generations of button-pushers who are basically playing video games and letting the machine do all the thinking. It takes a few brain cells to rub together and watch the progress of the resurfacing to follow the contour of the original shape and only remove enough material to get the surface smooth again without making a change in the original shape. Back when an automotive machinist might rebuild several sets of heads a day with those types of rockers just to pay the rent and put food on the table, he kept those skills honed to a fine degree. The fact that we're even discussing the procedure at all is a sad commentary on just how dumbed-down engine builders have become. "Buy new parts - - - -install- - - -hope for the best!"
Once the rockers are smoothed up, the best way to prevent further damage is to keep the valve adjustment correct. Mechanical lifter camshafts have an area of slow lift ground into the lobe called an "acceleration ramp" where the manufacturer's specified lash is slowly closed up before the valve actually begins to be lifted. Let the clearance get a little excessive due to ignorance or negligence, and the remaining clearance is taken up by the cam lobe violently slapping the rocker arm against the tip of the valve. The result is noise, and rapid wear.
Jerry
