Genuine BOSCH Distributor Rotor
Part number GB899

A rotor button is a component in the distributor system of a gasoline engine that is responsible for transferring electrical current from the ignition coil to the spark plugs. The rotor button is typically a small plastic or metal disc that rotates as the distributor shaft turns. As the rotor button rotates, its tip passes over a series of metal contacts in the distributor cap, which are connected to the spark plug wires. When the tip of the rotor button makes contact with one of the contacts, it sends a burst of high-voltage current to the corresponding spark plug, igniting the fuel mixture in the engine cylinder and producing combustion. Rotor buttons are critical to the smooth and efficient operation of gasoline engines, and must be inspected and replaced periodically to ensure proper performance.

In addition to transferring electrical current, the rotor button also helps to regulate the timing of the engine's ignition system. The tip of the rotor button is positioned to make contact with the distributor cap contacts at specific points in the engine's combustion cycle, based on the engine's timing settings. These timing settings are crucial to the efficient operation of the engine, and can affect its power, fuel economy, and emissions performance. A faulty rotor button can cause a number of problems, including misfires, reduced power, and increased emissions. Regular maintenance of the distributor system, including inspection and replacement of the rotor button, can help to ensure the continued reliable performance of a gasoline engine.