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Bosch 70A alternator bearing, commutator contacts replacement

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  1. Bosch 70A alternator bearing, commutator contacts replacement, Remove the regulator and check for wear: step 1, image 1 of 3 Bosch 70A alternator bearing, commutator contacts replacement, Remove the regulator and check for wear: step 1, image 2 of 3 Bosch 70A alternator bearing, commutator contacts replacement, Remove the regulator and check for wear: step 1, image 3 of 3
    • 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.

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  2. Bosch 70A alternator bearing, commutator contacts replacement, Disconnect contacts: step 2, image 1 of 3 Bosch 70A alternator bearing, commutator contacts replacement, Disconnect contacts: step 2, image 2 of 3 Bosch 70A alternator bearing, commutator contacts replacement, Disconnect contacts: step 2, image 3 of 3
    • 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).

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  3. Bosch 70A alternator bearing, commutator contacts replacement, Belt pulley: step 3, image 1 of 2 Bosch 70A alternator bearing, commutator contacts replacement, Belt pulley: step 3, image 2 of 2
    • 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.

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  4. Bosch 70A alternator bearing, commutator contacts replacement, Open the housing: step 4, image 1 of 1
    • 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.

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  5. Bosch 70A alternator bearing, commutator contacts replacement, Split the housing: step 5, image 1 of 2 Bosch 70A alternator bearing, commutator contacts replacement, Split the housing: step 5, image 2 of 2
    • Remove the four countersunk screws

    • Pull the rotor out of the bearing shield (housing).

    • Bearing shield and screws

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  6. Bosch 70A alternator bearing, commutator contacts replacement, Check rotor contacts (commutator segments): step 6, image 1 of 2 Bosch 70A alternator bearing, commutator contacts replacement, Check rotor contacts (commutator segments): step 6, image 2 of 2
    • 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

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    • This step is also necessary to replace the commutator ring

    • Remove the two bearings from the rotor shaft; a good bearing puller is helpful.

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  7. Bosch 70A alternator bearing, commutator contacts replacement, Remove the diodes and stator winding: step 8, image 1 of 3 Bosch 70A alternator bearing, commutator contacts replacement, Remove the diodes and stator winding: step 8, image 2 of 3 Bosch 70A alternator bearing, commutator contacts replacement, Remove the diodes and stator winding: step 8, image 3 of 3
    • 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).

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  8. Bosch 70A alternator bearing, commutator contacts replacement, Check stator winding: step 9, image 1 of 3 Bosch 70A alternator bearing, commutator contacts replacement, Check stator winding: step 9, image 2 of 3 Bosch 70A alternator bearing, commutator contacts replacement, Check stator winding: step 9, image 3 of 3
    • 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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    • Insert translation here

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Conclusion

Follow the steps in reverse order to reassemble your device.

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Silke

Member since: 07/24/19

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