Generator repair (Mercedes-Benz S-Class W116)

To install or repair a generator and the associated regulator, you must have some experience. If the generator is faulty, you must install a replacement unit until the old generator is returned from repair. Minor repairs, such as replacing the generator brushes, can be done in Bosch workshops.

The generator has bearings filled with long-lasting grease and does not require regular maintenance. The outer surfaces of the generator must be kept clean and protected from water or other liquids.

The generator brushes are in contact with smooth contact rings and are therefore durable. To check the brushes, if this work is being done for the first time, it is necessary to remove the generator. In a generator with a voltage regulator installed on the rear side, the work is performed in the following sequence:

Disconnect the ground wire from the battery and disconnect the plug from the generator.

Unscrew the brush holder/voltage regulator fastening (black box) to the generator and remove the brush holder. To avoid damaging the brushes, tilt the voltage regulator when removing.

Measure the length of the brushes as shown in Fig. 265. If the length of the brushes is less than 5 mm, it is necessary to unsolder the wires in the places shown by the arrows.



Solder the wires of the new brushes and assemble in the reverse order. Check the free movement of the brushes in the guides.



If the voltage regulator is installed separately from the brush holder, the generator must be removed and the brush holder dismantled. In this case, measure the length of the brushes as shown in Fig. 266.



With some experience, it is possible to disassemble the generator.

Disassembly

Using Fig. 267 as a guide, perform the following work:
Loosen the fastening nut from the rotor shaft and remove the pulley, fan and spacer washer. To do this, secure the generator in a vice, as shown in Fig. 268, and, holding the pulley from turning with an old V-belt, loosen the nut. Alternatively, you can secure the shaft with a hexagon inserted into the end of the shaft and loosen the nut. Remove the pulley with a puller. When installing the pulley, pay attention to its dimensions so that the pulley matches the engine model.





Remove the key from the shaft.



Unscrew the voltage regulator mount and brush holder and remove it.

(Material taken from a web resource: MercedesMAN)

Mark the position of the drive-side cover and the generator housing relative to each other and remove the two mounting screws from the housing. Disconnect the rear bearing cover from the front bearing cover. A plastic-headed hammer can be used to separate the covers.

Place the cover and rotor on a press and use a puller to remove the rotor, as shown in Fig. 269. To remove the bearing, unscrew the mounting screws from the inside of the cover and press out the bearing.



Press the bearing off the rotor shaft from the contact ring side. When using a puller, secure it to the inner bearing ring.

Unsolder the diode plate from the stator. To do this, clamp the wires with pliers at the soldering points to ensure heat dissipation. It is unacceptable to overheat the diodes.

Installation of diodes is only possible if you have the necessary equipment and work skills.

Checking the brushes and brush holder

Check the contact of the brushes and contact rings. Check the mobility of the brushes in the guides, if necessary, wipe the brushes with gasoline.



If the brush protrudes from the brush holder by less than 5 mm, it must be replaced. The measurement is made using a ruler.

Checking the rotor

Wipe dirty or greasy ring contacts with a rag soaked in gasoline. Polish random scratches on the working surface with fine sandpaper.

To check the insulation of the rotor winding, place one tip of the ohmmeter on the rotor core and the other on the contact ring. If the device does not show "infinity", the rotor must be replaced (see fig. 270).



To check the rotor winding resistance, place the ohmmeter tips on both contact rings. The ohmmeter readings should be within 2.8...3.4 Ohm. If the device shows "infinity", this means a break in the winding, with other readings it indicates a short circuit in the winding. In both cases, the rotor must be replaced (see fig. 271).

Stator check

During a short circuit, the damaged area becomes very hot, so the damaged area can be identified by visual inspection. In addition, install one ohmmeter tip on the stator plate and connect the other tip in series to the four terminals of the stator winding (see fig. 272). The device should show "infinity". To check the stator windings, it is necessary to check the resistance of each of the four windings (see fig. 273). The resistance value should be within 0.10...0.14 Ohm.

Checking diodes

Accurate testing of diodes is only possible using special devices in specialized workshops.

Generator assembly

Fig. 267 shows the installation of an alternating current generator, using which you can assemble the generator.