This procedure pertains to gasoline engines only.
The distributor performs two functions within the ignition system. Its breaker points or impulse sender (electronic ignition) time the collapse of the magnetic field of the ignition coil in relation to engine speed and convert primary voltage (12 volt) to secondary (high) voltage. The rotor and cap then distribute the high voltage spark to the correct spark plug.
The distributor incorporates both centrifugal and vacuum ignition timing mechanisms. Centrifugal advance is controlled by two weights located beneath the breaker plate. As engine speed increases, centrifugal force moves the weights out from the distributor shaft and advances the ignition by changing the position of the cam in relation to the shaft. This advanced positioning of the cam will then open the breaker points sooner and ignite the air/fuel mixture quickly enough in relation to piston speed. Centrifugal advance is necessary because as engine speed increases, the time period available to ignite the mixture decreases. (For example, at idle speed the ignition setting is, perhaps 10° BTDC. This is adequate for the spark plug to ignite the mixture at idle, but not at 2,500 rpm. The weights, governed by springs, move out at a predetermined rate to advance the timing to match engine speed.)
Centrifugal advance is not sufficient to provide the proper advance under all conditions, and so we also have vacuum advance. Under light load conditions, such as very gradual acceleration and low speed cruising, the throttle opening is not sufficient to draw enough air/fuel mixture into the cylinder. Vacuum advance is used to provide the extra spark advance needed to ignite the smaller mixture. The round can on the side of the distributor is the vacuum advance unit. The rubber hose supplies vacuum from the intake manifold to draw on the diaphragm in the unit which is connected by a link to the breaker plate in the distributor. Under part-throttle operation, the vacuum advance moves the breaker plate or impulse sender as necessary to provide the correct advance for efficient operation.
REMOVAL & INSTALLATION
See Figures 1, 2 and 3
- Unsnap the distributor cap clasps and remove the cap.
- Crank the engine until No. 1 cylinder is at Top Dead Center (TDC). At this point, the rotor should point to the spark plug wire socket for No. 1 cylinder, and the 0° timing mark on the crankshaft damper should be aligned with the pointer. For ease of assembly, scribe a chalkmark on the distributor housing to note the position of the rotor.
- Disconnect the primary lead from the coil at its terminal on the distributor housing. On electronic fuel injected models, disconnect the plug for the triggering contacts. On 1975 and later models with electronic ignition, remove the retaining screw for the primary voltage wire connector and pull it from the distributor housing.
- Label and remove the vacuum hose(s) from the vacuum advance regulator. Take care not to damage the connection during removal.
- On B20 and B30 engines, loosen the distributor attaching screw and hold-down clamp enough to slide the distributor up and out of position. On B21, B23, B27 and B28 engines, remove the distributor attaching screw and lift out the distributor.
- Perform the needed tests, repairs or adjustments on the distributor. If the engine has not been disturbed (the crankshaft was not moved since the distributor was taken out), install the distributor with the rotor pointing to the No. 1 cylinder spark plug wire socket, which should be in line with the chalkmark you make prior to removal. If the engine was disturbed, proceed to Step 7.
On the B20 and B30 engines, the distributor has an offset driving collar which can only be inserted one way. On the B21, B23, B27 and B28 engines, the distributor drive has bevelled gear teeth which will cause the rotor to turn counterclockwise as the distributor is installed. For this reason, it is necessary to back off the rotor clockwise (about 60° on the B21, B23, and 40° on the B27, B28) to compensate for this. When the distributor is engaged, the rotor must align with the mark made prior to removal.
- If the engine was disturbed after the distributor was removed, remove the spark plug for No. 1 cylinder and put your finger over the plug hole while you turn the engine over by hand. When you start to feel air pressure push against your finger, it means the cylinder is coming up on its compression stroke. With the engine on this compression stroke, turn the crankshaft around until the TDC mark on the harmonic balancer aligns with the timing pointer on the front of the engine. Install the distributor as explained in paragraph 2 of Step 6.
- Connect the primary lead to its terminal on the distributor housing. On electronic fuel injected models, connect the plug for the triggering contacts. On 1975 and later models equipped with electronic ignition, push the primary voltage wire connector into its slot in the distributor housing and tighten the retaining screw.
- Connect the vacuum hose(s) to the connection(s) on the vacuum regulator, (if so equipped)
- If the distributor was disassembled, or if the contact point setting was disturbed on models so equipped, proceed to set the point gap and/or dwell angle.
- Install the distributor cap and secure the clasps. Start the engine and set the ignition timing. See Engine Electrical . Tighten the distributor attaching screw.
Checking the Glow Plugs
See Figure 4
- With the engine cold, connect a test light between the glow plug terminal and ground.
Have an assistant sit in the car and turn on the ignition key to
) and observe the glow plug light on the dash board:
- If the glow plug light does not light and the test light does not light, it indicates a failure at the control unit.
- If the glow plug light does light but the test light does not, it indicates a failure at the glow plug relay.
- If the glow plug light does not light but the test light does, it indicates a failure at the temperature sender or at the control unit.
- Turn the ignition key to its 0 (off) position and remove the flat bar connector between the glow plug terminals. Connect a test light between the positive battery terminal and each glow plug terminal. If the test light does not light, it indicates a faulty glow plug.