Assuming you have hydraulic lifters. Solid lifters is a different issue. With engine running, lay rags over rocker arms to keep oil from spraying all over. Back off rocker nut until it clatters. Tighten until quiet, then tighten 1/4 turn at a time, pause until engine smooths out. Repeat until 3/4 turn. Repeat on all cylinders. Book calls for 1 full turn but we found 3/4 worked better. I was a "Certified" Factory Trained Technician back in the 1060's.
