I have a top end clicking noise.A mechanic told me it was a bad rocker assembly.I have one valve cover off (driver side). How do I ckeck to see if the rocker assem. Is bad. Or could it be a sticky lifter.I know the old way was to start engine and hold each tappet one at a time to see if noise quieted. Will that method work here on my 92 explorer, 4.0 pushrod engine. Not running and cold, the assembly is tite. No play at all.