How to Check a Motorcycle Statorby TJ Hinton
Generally, you can check motorcycle alternator stators while they're installed on the bike, using a quality multimeter. The tests will help you to identify or eliminate the stator as the problem in a charging issue. Since the regulator-rectifier cannot be tested, the only way to identify it as bad is to eliminate every other possibility first, so checking the stator is a necessary step in determining if you have a bad regulator.
Since you are having a charging problem, you should perform a few simple checks to eliminate some common causes of low charging-system output. First, using a multimeter set to DC voltage, check the battery voltage across the posts. If you do not have at least 12.5 volts, install a battery charger and charge the battery. Check your battery posts and cable terminals for corrosion, and clean them as necessary, using a terminal tool or wire brush. Check the condition of the cables. Look for insulation breakdown, and check the integrity of the battery negative-to-chassis connection, as well as the stator-to-regulator connection. Make sure the contact points are free of corrosion.
Static Stator Tests
First perform the static stator tests. With the ignition switch in the “Off” position, disconnect the regulator from the stator. Set the multimeter to “Resistance” or “Ohms” on the lowest scale, and insert one probe into one of the stator pin sockets. Touch the other probe to any chassis ground. If the display reads anything other than “Open” or the symbol for infinity, and shows any continuity at all, then you have a grounded stator and must replace it. Insert each probe into a stator socket. You should read around 0.2 to 0.5 ohms. If you show an open circuit with the “Open” or infinity reading or have higher resistance, then the stator is bad and you must replace it. If these tests all produce positive results, then the stator itself is good.
Dynamic Output Tests
The first dynamic test allows you to check the rotor that contains the magnets and spins around the stator. Any problems with the rotor will cause a loss of output. With the engine running and the multimeter set to check AC voltage, connect the probes to the stator sockets. Rev the engine up to 3,000 rpm and read the meter. If it is lower than 60 volts, then you need to replace the rotor. Now, connect the stator to the regulator. Set your multimeter to check amps on the lowest scale. Start the engine and turn on all electrical accessories. Disconnect the battery negative cable, and install the meter probes in series between the battery negative post, and negative cable terminal. If you read below four amps, and all of the previous checks are good, then you need to replace your regulator-rectifier.
Once you have the stator exposed, you can perform a visual inspection. Look for broken wires, thermal damage, or insulation breakdown on the coils. Inspect the outboard ends of the coils for evidence of contact with the rotor. Replace the stator as necessary. Pay particular attention to the stator for bits of magnet, and inspect the rotor carefully for broken magnets. The magnets usually cannot be replaced individually, so you must replace the rotor as a unit if it is damaged.
TJ Hinton trained as an auto mechanic at Mississippi Gulf Coast Community College and then later graduated from MMI as a certified motorcycle mechanic . He's also worked for 20+ years in home construction, remodeling and repair. His articles appear on InternetAutoGuide.com and TopSpeed.com.