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Do what Rick says! (Part 1: Brushes!)

Discussion in 'XJ Technical Chat' started by FinnogAngela, Oct 20, 2006.

  1. FinnogAngela

    FinnogAngela Member

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    Been having increasing troubles with uneven trottle response from idle to about 3000 rpms - and suspected carbs and/or faulty ignition. Then the other day a friend borrowed it and the bike died while riding - and wouldn´t start again. The starter motor took a couple of turns and then the relay just clicked.

    A nearby working roadlightworker came over and asked if he could help; he measured the battery to below 10V and the charging voltage above 2500rpms to below 12V.

    At home I took of the alternator cover and found one of the brushes to be broken off (it looks like)..(pic. 1)

    - and making quite a "scar" in the outer copper ring...(pic. 2)

    Luckily the brushholder was undamaged and a local mc-electromechanic wizard could grind 0.1mm off the copperrings (leaving just a tiny mark) (pic. 3)
    - and fit a couple of unoriginal (Bosch) brushes to the holder.

    The bike is now charging (a bit to much, actually, but according to Erik Schnabel, the electromechanic, that´s a common fault on these bikes and needn´t to be worried about during normal riding) and I´m good to go again (just need a better alternatorcover gasket..)

    So, as Rick has already stated: Check your brushes!
     

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  2. RickCoMatic

    RickCoMatic Well-Known Member

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    That spot you see on the rotor is a burn that's caused by the brush not having firm contact against the rotor.

    In this particular case; the arc generated enough heat to "Spot weld" the brush to the rotor. Most likely (if not certainly) at low rpm. The continued motion of the rotor snapped-off the brush and instantly opened the electrical connection preventing further damage.

    When this happens at higher rpm's ... the arcing continually scorches the copper ring until the copper surface of the ring is ruined and the rotor requires replacement!
     
  3. FinnogAngela

    FinnogAngela Member

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    Thanks Rick; from your explanation I can picture what happened - next time you write a "maintenence alert" I´ll probably do something about it sooner..
     

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