When I purchased my F-100 pickup with the 233 cu. in engine the valve train was incredibly noisy so I adjusted them to the factory spec. of .019". However afterwards the the rocker arm noise is just as noisy as before. My question is , is it harmful to the engine if I continue to use thinner and thinner feeler gauges until the noise is eliminated? I know it is possible to set the lifters too tight but I believe that I have quite a ways to go before reaching that point. Looking for some direction or advise. Many thanks.