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A rocker arm is a valvetrain component that typically transfers the motion of a pushrod in an overhead valve internal combustion engine to the corresponding intake/exhaust valve. Rocker arms in automobiles are typically made from stamped steel, or aluminum in higher-revving applications.
The lobed camshaft rhythmically presses against the lifter, which transmits the motion to the engine valve in one of two ways: through a pushrod which actuates the valve via a rocker mechanism (in an overhead valve (OHV) engine); via direct contact with the valve stem or rocker arm (in an overhead camshaft (OHC) configuration).
However, a desmodromic system must deal with the inertia of the two rocker arms per valve, so this advantage depends greatly on the skill of the designer. Another disadvantage is the contact point between the cams and rocker arms. It is relatively easy to use roller tappets in conventional valvetrains, although it does add considerable moving mass.
Since the 1960s, Italian motorcycle manufacturer Ducati has used a desmodromic valvetrain to counter this problem and allow for higher engine speeds by using positive closing as well as opening of the valves, without springs. The system consists of a mechanical lifter mechanism that uses a second rocker arm to push the valve closed.
Cutaway of a dual overhead camshaft engine 1969 AMC V8 overhead valve engine. The rocker cover has been removed, so the pushrods, rocker arms, valve springs, and valves are visible. A valvetrain is a mechanical system that controls the operation of the intake and exhaust valves in an internal combustion engine. [1]
Each rocker arm has a slipper follower mounted to the rocker arm with a spring, allowing the slipper-follower to freely move up and down with the high lobe without affecting the rocker arm. When the engine is operating below 6000-7000 rpm (dependent on year, car, and ECU installed), the lower lobe is operating the rocker arm and thus the valves ...
This engine employed pushrod-actuated rocker arms, which in turn opened poppet valves parallel to the pistons. Marr returned to Buick in 1904 (having built a small quantity of the Marr Auto-Car , with one of the first known engines to use an overhead camshaft design), the same year that Buick received a patent for an overhead valve engine design.
A Shelby Mustang Windsor V8 engine with "Cobra Powered by Ford" labeled rocker (valve) cover (lower left) A 4-cylinder Lycoming O-320 aircraft engine, with the rocker box cover of one cylinder (of the two visible) removed to expose its rocker arms for inspection. A rocker cover, (UK), or valve cover (elsewhere) is a cover that encloses the ...
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