![]() ![]() Some overhead camshaft engines employ short rocker arms, also known as fingers, in which the cam lobe pushes down (rather than up) on the rocker arm to open the valve. This rotates about the rocker shaft, and transfers the motion via a tappet to the valve. A similar arrangement transfers the motion via another roller tip to a second rocker arm. However, these generally have the roller at the point where the cam lobe contacts the rocker, rather than at the point where the rocker contacts the valve stem.įriction may be reduced at the point of contact with the valve stem by a roller tip. Roller rockers can also be used in overhead cam engines. ![]() This reduces friction, uneven wear and "bell-mouthing" of the valve guide. ![]() This rotation causes the other end of the rocker arm to press downwards on the top of the valve, which opens the valve by moving it downwards.Ī roller rocker is a rocker arm that uses needle bearings (or a single bearing ball in older engines) at the contact point between the rocker and the valve, instead of metal sliding on metal. The top of the pushrod presses upwards on one side of the rocker arm (located at the top of the engine), which causes the rocker arm to rotate. In the typical use-case of an overhead valve (pushrod) engine, the camshaft at the bottom of the engine pushes the pushrod upwards. ![]()
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