Types of rocker arm
1 stamped steel rocker arm
2 rollers tipped rocker arm
3 full roller rocker arm
4 shafts rocker arm
Rocker arms are typically in between the pushrod and the intake and exhaust valves. They allow the pushrods to push up on the rocker arms and therefore push down on the valves. However, in over head cam applications the cam will ride directly on the rocker arm.
In addition to just changing the the direction of the motion from up on the rocker arm to down on the valve, the rocker arm changes the amount of motion transferred. Typically a rocker arm will "multiply" its motion by a rocker arm ratio by a factor of 1.45 to 1.7, meaning that for each .100" of pushrod motion
