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Home Mechanical Engineering Automobile Engineering Lab Study of Ignition System Components-Coil, Magneto and Electronic Ignition Systems
Automobile Engineering Lab Lab Experiments

Study of Ignition System Components-Coil, Magneto and Electronic Ignition Systems


To test and trouble shoot the starting system used in automobiles.

Apparatus required:

Starting system.


The internal combustion engine is not capable of self starting. They are cranked by a small but powerful electric motor called cranking motor, starter motor. The starter motor is a DC electric motor.

The operation of a starter motor is explained below. When the driver presses the switch, current flow from battery to two coil windings like pull in winding and hold in winding. Both windings are energized (magnetic field). Initially to pull the plunger inward, due to the inward movement of the plunger touches the contact disk and close the circuit between the battery and starter motor.

When the contact disk touches the terminals of the starter motor the pull in coil is shorted out, thus no current flows through the coil. The pull in coil is de-energized. At the same time a small amount of current flow through the hold in coil winding. The magnetism produced by the hold in coil winding is sufficient to hold the plunger until the driver release the switch.


Testing the starting system.

  • Armature:Use a multimeter to check insulation between armature core and each segment which should be complete. The meter should also indicate continuity between each segment. Any short circuit in the armature winding may be tested with a growler. If the short circuit is indicated, the winding has to be replaced.
  • Field coils:Continuity should exist in the field windings which may be tested with a multimeter. There should also be perfect insulation between the yoke and the field terminal.
  • Brushes:Examine the brushes visually for wear and damage. If the wear or damage is more than the permissible limits, replace the concerned brush.
  • Brush holders:Use a multimeter to check the insulation between the positive brush holder and the holder frame. In case of any deviation from complete insulation, rectify the fault by repairing or replacing the damaged component.
  • Solenoid switch or shift:Disconnect the lead wire connecting the switch to the starter motor and apply battery voltage between the switch terminals. If correct, the plunger is attracted. In case of shift, the pinion would also project. It must be noted that the test should be done continuously for more than 10-15 seconds

Complete carburetor overhaul should be attempted by a skilled mechanic

  • First disconnect the lines and take off air cleaner. Then disconnect the linkage. Use two wrenches when disconnect the linkage. Use two wrenches when disconnecting the fuel lines, to avoid damage to threads. Keep the carburetor in a clean place where direct and dust cannot get into openings. Cover the exposed manifold holes with proper coverings. Do not use cotton waste to close the openings because thread of cotton waste may fall into the manifold. Covering the manifold is necessary because some time some nut bolt falls in the manifold hole un-knowingly and that cause a serious damage
  • Remove the carburetor as already explained and dismantle it carefully. Thoroughly clean the parts and all the jet holes by blowing air.
  • Check all parts for damage and wear. Check the float needle and seat for wear. Check the floats for dents or distortion. Check the bearing pin of the float. Power piston found scored should be replaced. Check the throttle and choke spindles bores for wear and out of round.
  • Inspect the idle mixture adjusting needle for grooves. In case it is defective it should be replaced. Check the pump plunger cup and replaced it if it is worn or hard.
  • Check the fuel filter and fuel screen for dirt or choking.
  • Check the entire gasket and their mating surface. In case the surfaces are rough these may be repaired.
  • Replace any parts that are worn, damage or excessively loose.
  • Put the carburetor into position on the intake manifold and fix it with the bolt and nuts. Connect the fuel line and distributor advance lines to the carburetor using two wrenches. Connect wires to switches and other electrical controls. Connect linkage and make idle speed, idle mixture and other adjustments. Install the air cleaner.
starter motor
starting system
ignition system