Bosch 70A alternator bearing, commutator contacts replacement

ID: 147213

Description: In order to overhaul the alternator with...

Remove the regulator: two screws (slotted in the original)
The carbon brushes should still protrude by at least 5 mm, otherwise replace the carbon brushes or the entire regulator. Here they are 12 mm.

On older alternators, the screws may be rusted solid. Spray generously with rust remover or penetrating oil and allow to soak in for a while if necessary.
Unscrew the nuts and washers (if present) on the two/four pull arms.
Unscrew the nuts and washers on the positive contact bolt (13 mm).
Unscrew the nuts, washers, and contact tongue from the control line (7 mm).
Unscrew the nuts, washers, and contact tab from the control line (7 mm).

Unscrew the belt pulley: hold it in place with an old belt and unscrew it with a wrench or ratchet. (22 mm)
Remove the nut and all washers as well as the fan blade, noting the order.
Remove the crescent key.

Mark the alternator housing for later reassembly.
If the four tie rods (screws) are of different lengths, note or mark where each one belongs
Unscrew the four screws (PH2).
Note: There are versions with four screws of the same length and versions with screws of different lengths.
Pull out the front housing part with the stator, using a plastic hammer to help if necessary.

Check: between the commutator segments 2.8 ohms +/- 10%, no contact with the housing?
Even if the resistance is correct, the contacts are so worn that the commutator ring must be replaced.
Wear limit: commutator ring diameter 27.8 +/- 1 mm, max. runout 0.03 mm

This step is also necessary to replace the commutator ring
Remove the two bearings from the rotor shaft; a good bearing puller is helpful.
This step is necessary to check the diodes
In the rear housing, remove the two screws that connect the diode plate to the housing
Pull the diode set and stator winding out of the housing
Do not lose the plastic bushing (or sliding ring).

Desolder the three stator cables.
Do not break the cables (e.g. by bending them).
Solder quickly (short and hot) so as not to fry the rectifier diodes.
Check the stator windings for short circuits to ground. Target: infinite resistance
Check continuity of the stator windings (the displayed 0.3 ohms) are inaccurate but continuity is present
Theoretically, the resistance of the windings (always 2 phases) can also be checked: should be 0.09 ohms +/-10%. However, this is not possible with a simple multimeter; 0.3 ohms is displayed here.

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