Ducati John

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Alternator Rotor Retaining Nut

The result of not routinely checking the alternator nut tightness.

Ducati recommend having the alternator rotor retaining nut tightness checked every 6,000 miles on bikes with the 2 wire alternator. It takes about an hour during the routine service to remove the nut clean it all up, loctite and re-torque it back up. Fortunately so far I've only come across a few bikes where the nut has come loose. Unfortunately it causes quite a mess as the photo shows. This rotor split damaging the alternator and its casing too. In bad cases it can render the crank useless too. More dangerously can cause the motor to seize, luckily (?) in this case only at 30 mph, but what if?.

The same can happen to the better designed system on 3 wire rotors too, mainly on hard used bikes such as race or trackday motors.

It is difficult to detect without removing the casing but usually causes a rumble form the alternator cover. Try running the motor with the bike in gear and clutch dragging (to quieten the bloody thing!!), the engine should be nice and quiet.

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