DYNAMO Removal and Installation

Dynamo removal is a straight-forward operation and is merely a matter of disconnecting the two leads from the rear of the unit and removing the mounting bolts. The unit can then be lifted away from the engine. When installing the dynamo, set the drive belt tension so that a free-play of approximately 1/2 in (13 mm) exists at the midway point along the longest belt run. If a replacement unit has been fitted, it should be 'polarised' before reconnecting the leads to the two terminals. To do this, connect a short lead between the two terminals on the dynamo and connect another longer lead to one of the terminals. At the starter solenoid, touch the other end of the long lead to the large battery feed terminal (opposite terminal to starter lead attachment) several times. The dynamo will now be correctly polarised to suit the electrical system. Remove the temporary leads and connect up the two dynamo leads to the large and small terminal respectively on the rear of the unit. Brushes Most faults associated with the dynamo are normally due either to the brushes or the rear bearing. In the latter case, excessive wear at the rear bearing bush allows the armature shaft to run eccentric and touch the field coils, in which case the complete unit is best exchanged. This condition is easily identified as excessive side movement at the rear end of the shaft when the drive pulley is moved side-to-side. To examine the brushes, unscrew the two throughbolts at the rear end bracket and withdraw the end bracket from the dynamo yoke. Check the condition and length of the two carbon brushes in the end bracket, and the condition of the surface on the commutator. If the brushes are worn to or are approaching their minimum length of 1/4 in (6 mm), they should be renewed. To renew the brushes, detach the old brush leads from the holders on the end bracket by removing the screw and lock washer. Note the positions of the terminal tags before disconnecting the leads. Ensure that the replacement brushes are of the correct type and length. Secure the new brushes in position on the end bracket. Inspect the contact surface on the commutator for signs of wear, burning or blackening of the segments. The latter indicates a short circuit. An open circuit will cause burned spots between the segments. Ideally the commutator surface should be smooth with a dark grey colour. If blackened or dirty, it can be cleaned up with a petrolmoistened cloth. Slight imperfections can be removed with fine glass paper - not emery cloth. Use the glass paper over the whole surface of the commutator. If the commutator is grooved, scored, pitted or badly worn, it must be skimmed down or replaced. Fit each brush into its holder in turn and check for freedom of movement. If a brush sticks, it can usually be freed by cleaning both the brush and the holder with a petrol-moistened cloth, or by lightly polishing the sides of the brush with a smooth file. Locate the brush springs on the side of each brush to hold them in the raised position. Check that the fibre thrust washer is in position on the end of the armature shaft, then refit the commutator end bracket. Ensure that the locating pip on the end bracket correctly engages the notch in the dynamo yoke. Fit the two through-bolts and tighten securely. Release the brushes onto the commutator by inserting a thin screwdriver through the ventilation hole in the end bracket adjacent to the brush holders and gently levering up the spring end on to the top of the brush. Before refitting the dynamo on the car, add one or two drops of light oil to the rear bearing through the hole in the centre of the end bracket. Do not overlubricate the bearing otherwise oil may be thrown onto the brush gear in use. Overhaul If any repair work, other than replacing the brushes, is necessary it will probably be more economical and convenient to have the dynamo repaired by an electrical specialist, or to exchange it for a replacement unit. If the unit is being exchanged, it will be necessary to remove the drive pulley as this will not normally be supplied with the new unit. After removing the pulley nut, the pulley can be levered off the keyed shaft, but care should be taken to avoid damaging the rim of the pulley.