What is "rocker arm"

Rocker \Rock"er\, n.

1. One who rocks; specifically, one who rocks a cradle.

   It was I, sir, said the rocker, who had the honor, some thirty years since, to attend on your highness in your infancy.
   --Fuller.

2. One of the curving pieces of wood or metal on which a cradle, chair, etc., rocks.

3. Any implement or machine working with a rocking motion, as a trough mounted on rockers for separating gold dust from gravel, etc., by agitation in water.

4. A play horse on rockers; a rocking-horse.

5. A chair mounted on rockers; a rocking-chair.

6. A skate with a curved blade, somewhat resembling in shape the rocker of a cradle.

7. (Mach.) Same as Rock shaft.

   Rocker arm (Mach.), an arm borne by a rock shaft.

n. a lever pivoted at the center; used especially to push a valve down in an internal-combustion engine [syn: valve rocker]

A rocker arm (in the context of an internal combustion engine of automotive, marine, motorcycle and reciprocating aviation types) is an oscillating lever that conveys radial movement from the cam lobe into linear movement at the poppet valve to open it. One end is raised and lowered by a rotating lobe of the camshaft (either directly or via a tappet (lifter) and pushrod) while the other end acts on the valve stem. When the camshaft lobe raises the outside of the arm, the inside presses down on the valve stem, opening the valve. When the outside of the arm is permitted to return due to the camshafts rotation, the inside rises, allowing the valve spring to close the valve.