Ignition Distributors

The distributor is a device for conveying electrical current to the sparking plugs according to the firing order. It comprises the contact-breaker with condenser, the ignition cam, the actual distributor, and an automatic timing control device which determines the optimum ignition timing suited to the operating conditions of the engine.

The distributor has a longitudinal shaft whose lower end is connected to a drive pinion in the engine block. This shaft is rotated at the same speed as the camshaft of the engine and carries the ignition cam, which actuates the contact lever.

This lever is rotatably mounted on a plate. Fitted to the upper end of the shaft is the distributor rotor, which is made of plastic and through which an electrode passes. The distributor disc is also the cover of the housing. At the centre it is provided with a carbon brush through which the current is passed to the distributor rotor. At the edge of the disc are a number of tungsten electrodes, one for each cylinder of the engine.

These are so arranged that the rotor is always at a contact just when the contact-breaker interrupts the circuit of the primary winding of the ignition coil. At that instant a high voltage is induced in the secondary winding of the ignition coil, and this voltage is allowed to pass through the rotor to the appropriate sparking plug.

 The condenser prevents the occurrence of sparking at the make-and-break contact. The ignition spark is produced as follows: so long as the make-and-break contact has not been opened by the cam, current can flow in the primary circuit (battery, primary winding, make-and-break contact, earth), so that a magnetic field is formed in the ignition coil.

At the instant when the contact interrupts the primary circuit, this magnetic field breaks down. This sudden change of the magnetic field induces a high voltage in the secondary winding, which voltage is thereupon applied to one of the sparking plugs, causing it to produce a spark.