Rocker arm generally referred to within the internal combustion engine
of automotive truck parts,
marine, motorcycle, car, truck parts and reciprocating aviation engines, the
rocker arm is a reciprocating lever that conveys radial information from
the cam lobe into linear information at the poppet valve to open it.
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 lowered by the camshaft, the inside rises, allowing the valve spring
to close the giver.
The effective leverage of the arm is determined by the rocker arm ratio,
the ratio of the distance from the rocker arm's center of rotation to
the tip divided by the distance from the center of rotation to the point
acted on by the camshaft or pushrod.
For car engines which use rocker arms are generally steel stampings,
providing a reasonable balance of strength, weight and economical cost.
Because the rocker arms are part of the reciprocating weight of the
engine, excessive mass limits the engine's ability to reach high