DISTRIBUTOR

Description

Distributor

The distributor handles several jobs. Its first job is to distribute the high voltage from the coil to the correct cylinder. This is done by the cap and rotor. The coil is connected to the rotor, which spins inside the cap. The rotor spins past a series of contacts, one contact per cylinder. As the tip of the rotor passes each contact, a high-voltage pulse comes from the coil. The pulse arcs across the small gap between the rotor and the contact (they don't actually touch) and then continues down the spark-plug wire to the spark plug on the appropriate cylinder. When you do a tune-up, one of the things you replace on your engine is the cap and rotor -- these eventually wear out because of the arcing. Also, the spark-plug wires eventually wear out and lose some of their electrical insulation. This can be the cause of some very mysterious engine problems.

The breaker points type distributor consist of the following component parts:

Breaker Section

Distributor Breaker Parts

Breaker points

Breaker Points

Damper Spring

Distributor Damper Spring

Distributor Section

Distributor Section

Distributor Cap

Distributor Cap

Rotor

Rotor

Ignition Advancer

Ignition Advancer

Vacuum Advancer

Vacuum Advancer

Octane Selector

Octane Selector

Condenser (Capacitor)

Capacitor / Condenser

Types of ignition system other than the breaker points type distributor are listed below.

* In the transistorized ignition system, the breaker section of the breaker points type distributor is changed     from mechanical to electronic.

* In an ESA (Electronic Spark Advance) system, the breaker section and ignition advancer of the breaker points type distributor are changed from mechanical to electronic.

* In the DLI ( Distributor-less Ignition) and DIS (Direct Ignition System) types, multiple ignition coils are used in place of distributor to provide high voltage to the spark plugs.
Older distributors with breaker points have another section in the bottom half of the distributor -- this section does the job of breaking the current to the coil. The ground side of the coil is connected to the breaker points.
A cam in the center of the distributor pushes a lever connected to one of the points. Whenever the cam pushes the lever, it opens the points. This causes the coil to suddenly lose its ground, generating a high-voltage pulse. The points also control the timing of the spark. They may have a vacuum advance or a centrifugal advance. These mechanisms advance the timing in proportion to engine load or engine speed.Spark timing is so critical to an engine's performance that most cars don't use points. Instead, they use a sensor that tells the engine control unit (ECU) the exact position of the pistons. The engine computer then controls a transistor that opens and closes the current to the coil.
In the next section, we'll take a look at an advance in modern ignition systems: the distributorless ignition.

BREAKER SECTION

1. Breaker Point Operation

Breaker Points Operation

The breaker points are opened and closed by the cam installed on the distributor shaft. The distributor shaft is driven by the camshaft at half the engine speed. The cam has cam lobes identical in number to the engine cylinders. As the cam rotates, each cam lobe pushes the breaker points. As the cam rotates further, the breaker arm is returned by the breaker arm spring to close the breaker points. As the cam makes one full rotation, the current flowing in the primary winding of the ignition coil is interrupted as many times as the number of engine cylinders to generate a high voltage in the secondary winding of the ignition coil.

2. Breaker Point Requirement

Point Gap

The following conditions are required to obtain a sufficiently high secondary voltage:
*  Adequate primary current must be allowed to flow even when the engine speed is high.
 *  The primary current must be able to be interrupted instantaneously.
But the contracting surfaces of the breaker points are burnt by the high-tension sparks produced by the self-induced electromotive force of the primary coil, and oxidation develops. In addition, if the opening angle of the points becomes too small due to wear of the rubbing block, the point gap will become too small, thus causing the primary current to be unable to be interrupted instantaneously due to sparking between the gap. Therefore, breaker point must be checked periodically and replaced if excessive oxidation or other related problems are found. The breaker points are essential to good engine performance, so they must be checked, with attention paid to the following points.

    *  Breaker point contact resistance
    *  Rubbing block gap
    *  Dwell angle

BREAKER POINT CONTACT RESISTANCE
 
1. Oil/Grease Adhesion to Contact Surfaces
 The adhesion of these substances to the breaker points causes burning due to arcing and an increase in contact resistance. Therefore, care should be taken not to get oil or grease on the breaker points when they are replaced.
2. Incorrect Point Contact Alignment
Incorrect point contact alignment reduces the point contact area, accelerating point oxidation and point surface wear.
Therefore, be sure never to bend or otherwise deform the breaker baseplate or breaker arm.

REFERENCE
Grease is supplied with the TOYOTA distributor replacement point kit (breaker points). When replacing the breaker points, apply small amount of this grease to the breaker arm rubbing block (heel). This smooths contact with the cam to reduce rubbing block wear. Apply it carefully, However, as excessive application will cause the grease to spatter and contaminate the breaker points.

Rubbing Block