DISTRIBUTOR ASSEMBLY:

The distributor assembly is made up of several subassemblies: the cap, rotor, breaker plate assembly supporting the breaker points and condenser, cam, centrifugal mechanism, vacuum advance unit and the distributor base or body.

The distributor cap and rotor are used to distribute the high voltage current developed in the coil to each spark plug in firing order sequence. The distributor cap is keyed to the distributor body to maintain the correct relationship between the distributor cap towers and the rotor. The rotor is keyed to distributor cam to be in the correct position to transfer the high voltage current to one of the distributor cap high voltage towers when the points open.

The breaker plate supports the breaker points at the correct position for the cam to open them. In most distributors, the breaker plate is moveable and is mounted on a center bearing or side pivot. Since a moving part can develop high resistance at the bearing surface, a flexible insulate wire is used to connect the points to the primary circuit. Also, a grounding wire is used between the plate and distributor housing.

The distributor cam opens the breaker points to interrupt the primary circuit. The cam has the same number of lobes as the engine has cylinders as the points must be opened to produce a high voltage surge for each power stroke. The distributor cam is actuated by the weights of the centrifugal advance mechanism.

DISTRIBUTOR ASSEMBLY

The centrifugal advance mechanism varies the position of the cam in relation to engine speed. The mechanism has weights that are thrown out against calibrated springs to advance the breaker cam as speed increases. The advance mechanism is usually mounted in the distributor housing below the breaker plate.

The vacuum advance unit advances the ignition timing in addition to the advance provided by the centrifugal unit. The vacuum unit is controlled by manifold vacuum and consists of a metal chamber in which a flexible air-tight diaphragm is located. A link extends from one side of the diaphragm to the breaker plate assembly or distributor housing. If the distributor is equipped with a moveable breaker plate, the vacuum advance mechanism rotated the plate to advance the ignition timing. If the plate is rigidly mounted in the distributor, the vacuum advance unit rotates the complete distributor assembly for advance.

The lower drive end of the distributor shaft is equipped with either an offset grove or tang or with a gear, depending on the manner in which the distributor is driven. The reason the tang is offset is to assist in correct installation of the distributor when replacing it in the engine.

The base assembly or body serves as a housing for all the parts mentioned and also serves as the bearing for the distributor shaft. The bearing may be cast iron, bronze or ball bearings. The base is also the adapter for installing the distributor assembly in the engine block. The base can be rotated in either direction to make the initial timing adjustment.