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techtips #2: the xs650 charging system

Welcome to our new series, techTips. Two makes a series, damnit. This is our second installment and was written by a nameless metric mechanic. Welcome to the XS650 Charging System:

The XS650 is probably one of the best classic motorcycles you could ever buy if you want a reliable and easy to maintain bike. It is nearly everything that a Triumph should have been; a leak free, easy to maintain vertical twin. The XS650 has a few weak points though, the clutch (usually hard to get into neutral because of poor adjustment), the sheer weight of the machine (especially the later Specials), the ignition system (weak coils and dual points on pre-’79 models) and the charging system.

Sadly, the XS650 suffers from not having a permanent magnet charging system, so this is a helpful step-by-step way to find where the problems are. Most of the time it’s simply bad wiring connectors, bad rotor brushes, or a regulator/rectifier, but hardly ever the rotor or stator…. except on one of my bikes it was the rotor, because it just had to be difficult.

1. Battery Test
First charge the battery to at least 12.5 volts. If the battery won’t keep a charge for a day without riding the bike, it’s screwed. If it won’t charge to 12.5 volts, it’s screwed. if you live in Texas and it hasn’t been used for over a year, it’s screwed. If you live near water and….

Batteries have a life of between one and three years normally, and without use, the life span is considerably shorter. Intense heat and cold makes this more pronounced. If you are actually going to rely on this bike as regular transport, then the sealed AGM batteries have a longer life and more cranking power, and they are worth the extra money.

2. Charging Test
Start the engine and connect a DV volt meter to the battery and see what you get. At anything over 2500 RPM, it should be in the 14 to 14.7 volt range. If it has trouble getting over 14 volts, there’s an issue. Get a new battery.

3. Magnetic Field Test
To check if your generator is creating a magnetic field (the XS needs battery power to create a magnetic field, which in turn creates power), find a thin feeler gauge and hold it about half an inch away from your generator cover (on the left side as you sit on the bike). Now turn the ignition on. If the regulator and rotor are working, the feeler gauge should be drawn to the casing when the ignition is turned on. Magnetism! If nothing happens or it hardly moves then the rotor is not creating the field, so it’s on to the next step:

4. Rotor Power Test
Remove the generator cover (the two screws holding the round “YAMAHA” plate) and with a DC volt meter, test the voltage at the brush terminals. The inner one is + and the outer is . You should be getting the same voltage as your battery, or at least within a volt or so. If it’s not within this range, it’s either the wiring to or from the ignition switch, or it’s the regulator not supplying a full charge to the brushes.

On the solid state regulator models (post 1980), all you need to do is locate the green wire at the regulator plug and connect it to ground. This will bypass the regulator and allow full voltage to the brushes. Test the bike running again (providing you get good voltage at the brushes) and if you get a good charge on the battery, Yay!

Earlier (pre-1980 models) have a mechanical type regulator and separate rectifier, which suck and should be replaced with a solid state one.

By the way, the stock ones on post 1980 XS’s will not work on earlier models, in case you were thinking that.

5. More Rotor Testing
If you can’t get close to battery voltage on the two rotor brushes, then it’s probably the wiring to and from the ignition switch or the regulator. Check the wires for bad connections to and from the switch and obviously fix any issues, and don’t use those horrible Home Depot crimp connectors or even worse, splice connectors. Get some good connectors or solder broken wires; after all, you wouldn’t like to have your limbs held on with a slice connector, so why do it to your wiring?

If you’re getting good voltage at the brushes, but no charge, remove the brushes (the four small screws) and measure the length of the brushes. If it’s anywhere near 7mm or less, replace them. While you’re at this, use some alcohol to clean the slip rings. A buildup of grease and **** will effect how the current is able to pass through to the rotor.

Next, while the brushes are out, test the resistance for the rotor between the two slip rings (the shiny brass rings). You should get about 5.5 ohms. Any less and it’s toast, so buy a new one. If you get the magic number, connect one tester lead to either slip ring and a bare metal part of the engine. You should now get an infinite reading on your ohm meter.

6. Stator Test
To test the stators output, run the engine at idle speed – remember to connect everything back up – and use an AC voltmeter (A DC voltmeter won’t be able to test this) to test between the three white wires from your stator at the connected plug. You should get 10-11 volts AC on each combination of white to white. If you get much under 10 volts AC on any of the three tests, then something is grounding your stator. Sadly, it’s probably time for a new stator at that point, but carry out the tests in the next section to make sure. If you get over 16 volts AC, the regulator isn’t doing its job, so replace it.

7. More Stator Tests
If you get low voltage on any of the white-white AC tests, unplug the connector and use an ohm meter to check the windings. Check the resistance between the three white wires, making sure you are on the correct side of the connector (the stator side). On each white to white connection you should be getting about 0.4 to 0.5 ohms. If you get a low reading on all of the three combinations, find the yellow wire and disconnect it. Re-check the resistance on all three combos. If the readings are good, then the yellow safety relay is ****. To be honest, you can pretty much forget about the safety relay, disconnect the yellow wire, and throw it in the trash if this is the problem.

If you see improvement in just one or two readings after disconnecting the yellow wire, then check the offending white wires by connecting your ohm meter to it and the engine. You should get a high or infinite reading. If you still get a low ohm reading, check that none of the wires have been stripped or rub the engine anywhere along their length. If all your wires are pretty and not being earthed in any way, your stator is toast and should be replaced.

8. The My Bike Hates Me Test
If everything seems in order, but you still don’t get a good charge at the battery, check to see if you see if you have any unnecessary chrome or leather tassels on your bike. If you find any of these things, it might be that your XS650 now hates you and doesn’t want to be seen in public.

Other things that might cause this are:
1. Ape hangers over 12 inches high
2. Flames
3. Skulls
4. Flames and Skulls!
5. “Maltese” crosses
6. No front brake (Your bike loves you and does not want you to die…. yet.)
7. Sissy bars
8. King & queen seats
9. Any inappropriate bling
10. Sportster gas tanks.

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This concludes our emergency XS650 Charging System test. Had this been an actual emergency, you would have been instructed to provide your credit card, address, phone number, social security number, PayPal password, bank routing number, mother’s maiden name, favorite sports team, and first-born child.


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One comment

  1. Disconnecting the yellow safety relay wire shuts the headlight off.

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