I have a question about valves. My 93 has 206,000 miles. The rocker arms are not adjustable. The Arms are pretty worn, but are getting alot of pre-load on the lifters. I do not have a bleed down tool to check valve clearance, but do valves get tighter with age? I would think just the opposite, but maybe the valves sink deeper into the head with wear. I have a tapping noise when the engine is underload, It comes and goes and isnt a exhaust leak. I have located it to be the #7 cylinder. IF I unplug the # 7 injector the noise goes away. I thought a wrist pin but wouldnt a wrist pin knock all the time when under load? I am thinking maybe the valves being too tight and a intake or exhaust valve hanging open sometimes. I am thinking if it was a bad lifter it would do it all the time even if the engine wasnt under load. The engine runs great and uses very little oil and 60psi of oil pressure hot.