1942 - 1947 Chevrolet Shop Manual



	12-23

	The switch contacts are so arranged as to provide a wedging action when contact is made thus insuring a good connection, and also giving the contacts a wiping action which tends to keep them clean. DRIVE MECHANISM The drive pinion and over-running clutch is a self-contained unit. If it becomes damaged in any way the complete unit should be replaced. However, should the spring be broken or the sheave become worn, these parts may be easily replaced by compressing the spring to uncover the lock ring	reversing switch, through the switch to the distributor, across the breaker points and back to the grounded terminal of the reversing switch, and back to the negative terminal of the battery, Fig. 51.


	Fig. 50-Starting Motor Drive Mechanism in the tube part of the drive mechanism. Removal of the lock ring permits removal and replacement of both the sheave and spring. Fig. 50 shows a layout of the drive mechanism parts. THE IGNITION SYSTEM The power in a gasoline engine is derived from the explosion of gas in the engine cylinders. In order to explode this gas, an electric spark is made to jump a small gap inside the cylinder or combustion chamber. The ignition system furnishes this spark. The spark must occur in each cylinder at exactly the proper time and the sparks in the various cylinders must follow each other in the proper order or sequence. To accomplish this, the following parts are used: The battery which furnishes the electrical energy; the ignition coil which transforms the battery current to high tension current which will jump the gap in the spark plug; the mechanical breaker which opens and closes the primary circuit at the proper time; the distributor which delivers the spark to the proper cylinder; the spark plug which provides the gap for the spark to jump in the engine cylinder: the wiring which connects the various units; the ignition switch for disconnecting the battery when it is desired to stop the engine. OPERATION When the ignition switch is closed, current flows from the battery positive to the starter switch, over the wire to the ammeter and then to the ignition switch, through the switch to the coil. The current now passes through the primary winding to the
		Fig. 51-Ignition Circuit
		Current flowing through this circuit builds up a magnetic field about the coil. When the breaker points open, the current tends to keep on flowing and surges into the condenser, attracting a positive charge on one side and a negative charge on the other. A fraction of a second after the breaker points open, the counter pressure in the condenser overcomes the surge pressure on the line and the condenser discharges from the positive charged side back through the primary winding of the coil in the opposite direction to the primary current, through the battery to the ground and back to the grounded side of the condenser, equalizing the two sides of the condenser. The discharge current from the condenser, passing over the primary winding tends to reverse the polarity of the coil and results in a very rapid demagnetizing of the coil. This rapid movement of the lines of force across the large number of turns of the secondary winding induces a current of very high voltage, which flows from the secondary winding to the high tension terminal of the coil, then to the distributor, across the distributor rotor to the spark plug, across the gap between the plug points to the ground and back to the other end of the secondary winding, completing the circuit. CONDENSER The operation of the condenser is many times misunderstood by the average service man. It is one of the most important units in the ignition system. In order to understand its action and function, we will show a water analogy of condenser action.