Rocker Arms
Rocker arms are made of stamped steel, cast iron, or aluminum. Some engines do not use rocker arms. The camshaft on these engines ride on a tappet placed directly over the valve. There are three types of rocker arms used on today's vehicles:
Stud mounted: These rocker arms are fastened to a stud by a pivot ball and a stud nut. This rocker arm will typically wear in three contact points. Look at the socket where the pushrod 
rides. If this area is shinny this is considered normal wear. This end lubricates the rocker arm/valve through a hole in the rocker arm, a hollow pushrod, and a hydraulic lifter. If this area is pounded out and forming a ridge the entire rocker arm must be replaced. The valve tip side of the rocker arm should be inspected in a similar fashion. If the area in the center of the rocker arm or the pivot ball show excessive wear both rocker arm and pivot must be replaced.
Pedestal mounted: These rocker arms are similar to stud mounted except the arm pivots on a fixed shaft. These individual rocker arms are fastened to the head as an assembly. Inspect these rocker arms just as you would a stud mounted unit.
Shaft mounted: These rocker arms are mounted on a shaft and removed from the cylinder head as a single unit. Once removed from the 
head each rocker arm, spring, and spacer should be inspected. The shaft should be checked for straightness on a flat surface. Also check the shaft for ridges. If the surface has a shinny look where the rocker rides it is acceptable. If the shaft is bent or has formed ridges it must be replaced.
Excessive valve lash will cause damage to the ends of the rocker arm. These surfaces are usually hardened for durability. Studs on stud mounted rocker arms can become worn or loose. These are often replaceable: a special tool is used to remove these studs and a new stud is pressed in.