How to Check a Motorcycle Stator
The stator is the stationary part of a motorcycle's alternator. It consists of a series of wire coils arranged in a ring around the alternator's rotating flywheel. As part of the alternator, the stator is responsible for generating electrical energy from the mechanical energy of the motorcycle's engine, which is then used to run the electrical systems and charge the battery as needed. When the stator malfunctions, a motorcycle can experience problems such as a misfiring engine, a dead battery or an inability to start. There are several possible failure points on a stator, and when diagnosing electrical problems on a motorcycle, it is important to check for all of them.
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Instructions
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Check the coils of the stator for any discoloration or scorching. These can occur when a wire in one of the stator coils breaks or develops a short. If discoloration or scorching is present, the stator will need to be repaired or replaced.
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2
Check the plug connecting the stator to the voltage regulator. Dirt or corrosion in the plug's connections can lead to dropped voltage, lowering the efficiency of the stator and eventually damaging the plug. The plug may also be melted due to this kind of dropped voltage. A dirty plug should be thoroughly cleaned, while a corroded or melted plug will need to be replaced.
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3
Check the resistance across the pins of the plug using a multimeter. Set the multimeter to the "OHM" setting and touch a probe to the inside of any two pins in a vertical pair. There should be between 0.1 and 0.2 ohms of resistance. A resistance of zero indicates a short in the plug. A resistance of infinity indicates a broken connection inside the plug.
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Measure the resistance between the plug's pins and the ground. Leaving the multimeter on the "OHM" setting, touch one probe to a section of bare metal on the motorcycle's frame and the other probe to each of the plug's pins in turn. The needle of the multimeter should not move. If the needle moves, indicating a connection between the stator and the frame, the stator is improperly grounded due to a break in the wiring and should be replaced.
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Start the engine. Set the multimeter to measure A/C current at a threshold of 30 volts. Test the A/C output of the plug by touching a probe to each of the pins in a vertical pair, being careful not to let the probes come into contact with one another. The multimeter should give a reading of between 16 and 20 volts when idling. If the reading is lower than this, the stator is not putting out sufficient power and should be replaced.
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Tips & Warnings
The electrical measurements given in this article are very common, but not universal. Check your owner's manual to get the manufacturer's measurements of resistance and A/C output for your motorcycle.
The most common electrical problem in motorcycles is a bad battery. A motorcycle with a bad battery will run, unlike a car, but it will run badly. Make sure your battery is fully charged and properly connected before moving on to the stator.
Allowing the probes of a multimeter to come into contact with one another while testing active voltage will cause a short, possibly giving you a shock and damaging both the stator and the multimeter.
