TDM900 : How to replace the alternator stator


Problems with the alternator may appear, mainly on machine with more than 100.000km and/or subject to high temperature.

The issue is caused by a faulty stator :
• coils shorted to the chassis - the most common failure.
• a coil winding is broken.
• a coil is in short-circuit between some windings.

This was the latter which happened on my bike : the charging voltage at idling was 12.9V ~ 13.0V.
Such voltage is not high enough to charge the battery correctly but you may ride a few hundred kilometers (without the headlight on) before it goes empty & the engine stops.

Preamble

Find a safe, well illuminated and stable place and use the central stand or any suitable stand, get good quality tools : a good quality ohmmeter (Metrix, Fluke, etc) or a milliohmmeter. A cheap ohmmeter will not measure a low resistance correctly.

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Testing the stator

1 - Testing the insulation from the chassis

Check out if the stator has short-cuts to chassis (the most common failure, it happened twice on my bike in 200.000 km / height years).

Pull out the stator harness connector (located under the seat, attached to the regulator) and wire test leads on one of the three terminals and the other one to the chassis : in case it displays zero Ω the stator is knocked out, there is no more insulation from the chassis.

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Test continuity between the chassis and each terminal inside the stator harness connector.

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A stator in good working conditions must be insulated from the chassis (the pic shows a new stator in good working condition).
When using the ohmmeter, it will display an infinite resistance "1".

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2 - Testing the coils winding resistance

Test each coil winding resistance.
Standard resistance must be 0.18Ω to 0.28Ω.

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Replacing the stator

Remove all parts / covers before removing the alternator cover.

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Remember the position of the gearbox shaft washers...

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Time to remove all that mess !

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Drain the engine oil from the alternator side only.

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Put another bowl under the engine and remove the cover.

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In case the cover don't come easy you may use a rubber mallet - use gently !
Be careful because the strong magnets on the rotor keep parts assembled.

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Locate the harness of the crankshaft position sensor and plug it off.

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Then disassemble the stator harness (in my case I couldn't it take apart so I left only the wires).
Be patient and use adapted tools.

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Gently pull the wires and remove the whole cover.

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Now disassemble the stator and the crankshaft position sensor from the cover.

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The right side of the stator looks like it burned !
This is actually the top part of the stator which is not dipped in the engine oil.

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On the left-hand side : the new stator.
On the other side : the old stator. It is 100.000km old and present a short-cut to the chassis.

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Clean parts, replace the stator.

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Use Loctite on each screw.

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Use bond sealant on the wiring pass-through hole.

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Replace the crankshaft position sensor.

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Route the stator / crankshaft position sensor wiring.

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I wrapped the wires inside a silicon housing to protect them against vibrations & heat.

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Ok, now clean the mating surfaces.

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This is the old seal. A new one is normally required but you may re-use the old one in case it's still in good condition.

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In case the old seal is used, put engine seal bond.

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Replace the stator / cover assembly.

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Route the stator / crankshaft position sensor harness.

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Testing the good job

Connect alternator / sensor connectors and start the engine.

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Check the regulator charging voltage : it must be around 14.5V at idle.
Check again the charging voltage the day after.

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Check the battery voltage (main switch off), it must be over 12.8V.
In case it presents a lower figure, the battery needs to be replaced (below 11.8V) or you have too much idle current draining : check the electronic alarm and any other devices wired directly to the battery.

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Original text & pics in this page are from Marco (Italy).

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