A rocker arm is an oscillating lever in internal combustion engines that translates radial motion from the cam lobe into linear motion to open a poppet valve. It operates by moving one end to press down on the valve stem while the other end is acted upon by the camshaft's rotation. Various materials, including steel and cast iron, are used in rocker arms, with design considerations focused on reducing weight to enhance engine performance at high speeds.

2. ROCKER ARM.

3. USE AND WORKING ROCKER ARM.
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 lifter and pushrod) while
the other end acts on the valve stem.

4. USE AND WORKING ROCKER ARM.
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.

5. USE AND WORKING ROCKER ARM.

6. ROCKER ARM.
For Ic engines the rocker arms are
generally steel stampings, providing a reasonable
balance of strength, weight and economical cost.
Truck engines (mostly diesel) use stronger and
stiffer rocker arms made of cast iron (usually
ductile), or forged carbon steel.

7. ROCKER ARM.
Because the rocker arms are, in
part, reciprocating weight, excessive mass
especially at the lever ends limits the engine's
ability to reach high operating speeds.

8. ROCKER ARM.
Many lightweight and high strength alloys,
and bearing configurations for the fulcrum,
have been used in an effort to increase the
RPM limits for high performance
applications, eventually lending the benefits
of these race bred technologies to more high-
end production vehicles.

9. ASSEMBLY OF ROCKER ARM