81 xj550 project

In practice it's a test from almost every factory service manual I've ever looked at.

 

Thanks. I didn't come across it in my manual yet but maybe because I read an online version and not my actual book.

Well that sucks then. I don't get a magnetic field. But good in respect that i now know where the issue seems to be coming from and where to look first.

 

I saw the post in another thread just now. Your stator is bad.
The rotor is likely good, but if you an snag one as a package deal with a stator (and not overpay) it wouldn't hurt to have one.
Replace the stator.

 

Thanks. I'll start a conversation with Len.

 

New stator came in from Len but no good.
Just to make sure I am not doing something wrong when reading the resistance. The meter has to be set like this, correct?



So, on the new stator, I am getting 1.0 across all three white wires. This is still out of spec, no? It's supposed to be in the 0.5 range.
On the rotor, I am getting 5.5 across the two rings. I couldn't get any reading on the connector today for whatever reason. I did two days ago.
The brushes are clean but might be short. They are only about 1.2cm but I haven't found specs for length in my manual yet.
I wanted to remove the rotor for a visual inspection but didn't manage because it kept rotating. Need to build or order a tool.

Not sure where to go from here since the two parts (rotor and stator) are out of spec but stator is new and should be fine?

Edit: I didn't measure the brushes end to end (just realized) and according to the wear line, I have plenty left.

 

And just for the completeness of the info, the rotor does spin when engine runs.

 

Stupid question:
Does the rotor get any power from somewhere or is this not needed?
Just trying to think if the issue is somewhere else.
It just spins when engine is running which then creates a magnetic field because of the stator? And that is send over rectifier to battery.

 

18 resistance at brown green wire. Which indicates something is up with the wiresor brushes. At the rings, I had 5.5.
I will also check the multimeter. I was thinking that if, for whatever reason, the ohm readings are off by .5, everything would fall into specs.
But this still wouldn't explain not getting a magnetic field that can be tested with the feeler gauge - unless, hence my question above, if it actually needs a power supply first. Which would then lead me away from the alternator in general and look for something else.

And my apologies for all the posts, just trying to think through stuff and write it down as additional info

 

Digital multimeters like that one may not be very accurate at low resistance readings.

The spinning rotor must be engergized (voltage fed to it) for it to create a magnetic field.....the rotor is really an ELECTRo-MAGNET, i.e. it doesn't become a magnet, nor produce magnetic fields, when no "electro" is fed thru it....and the delivery of electricity to it is the purpose of the brushes which ride on the copper rings on the face of the rotor.....the brushes carry/transmit voltage to (and ground from) the rotor, thus "energizing" the rotor and creating a magnetic field within it. No voltage to the rotor = no magnetic field.

The spinning action of the rotor merely takes the created magnetic fields in the rotor and rotates them past the stator. Non-moving (or, more precisely, non-fluctuating in strength) magnetic fields don't do much for the generation of electricity; VARYING STRENGTH magnetic fields will induce an electrical current in a conductor (i.e. a wire, or a big mess of wires such as the stator). The "varying strength" of the magnetic field(s) is due to the fact that the rotor is rotating, thus bringing (and then removing) a magnetic field past the stator's wires. Of course, this magnetic field isn't very strong, but it does not have to be: there are lots of wires in the stator, and each one of them gets a "to-and-fro" magnetic field strength from the rotating magnets/magnetic field in the rotor, and so in total it adds up to the required voltages needed.

The amount of voltage applied to the ROTOR is controlled by the voltage regulator; the lower the voltage of the battery, the more voltage it applies to the rotor (via the brushes, thru the commutator rings) and thus "amps up" the magnetic field strength of the rotor. The higher the magnetic field strength of the rotor, the greater amount of voltage flow is induced in the stator and thus fed from the stator, to the voltage rectifier (which changes the AC current coming out of the stator to DC current), and then to the battery.

 

Get a resistor that you know the value and tolerance of. Read the resistance with the meter.

I have the same meter as you do (as a spare) and it's pretty close to my Simpson, but then part of what you pay for when buying an expensive meter is consistency and repeatability from every meter they manufacture. I may have goten lucky with the particular Actron meter that I have.

 

Ooookkkaayyyy...
Thanks guys.
So basically:
Verify the multimeter is giving correct numbers
Check wires to/from brushes
Check regulator/rectifier and all wires there

I'll do that over next few days
Thanks again

 

Got myself something nice (and expensive).
Arrived yesterday

 

I'm drooling

 

Best you can do when measuring the stator is subtract the resistance of the leads and contacts from the actual reading. So, touch one of the stator wire terminals with both leads with the leads not touching and note that reading - wiggle the leads a bit to get the lowest reading. Then measure the stator resistance as instructed in the FSM. Subtract the first reading from the second to get very close to actual stator resistance.

Be sure to use a thin feeler gauge to test for rotor excitation. About a 1/4 inch away from the AC generator cover and when the key is turned on the feeler gauge should pull towards the cover. The rotor should be receiving maximum excitation when the engine is not running. 12V ignition on the brown wire, and approximately 1.8V on the green wire. The regulator controls the low side (green wire) and will raise and lower the voltage based on internal voltage sensing within the regulator.

Reading a higher resistance (up to about 20 ohms) at the brown / green wire connector is not all that unusual. I get a reading of about 18 ohms on mine, but if I insert a current meter and check current the actual resistance calculates to about 5 ohms.

 

Well, I guess mine (speedo) is wrong. I could have sworn I did a lot of research and came up with this number. Maybe I ended up ordering the wrong one.
Mine already shows 8 miles on it and I didn't even ride it that much.

 

8 miles isn't very far. A tour around my block is almost a mile.

 

And the Oscar goes to: hogfiddles

Dave suspected the rectifier right from beginning.
I had a new one on there but it was no good. Received my new part yesterday and just put it in. Feeler gauge is getting attracted now.
I haven't checked the voltage going to battery yet but it looks promising.

Only thing left now is the front brake.

 

I have to say, every time I turn on the bike, I am amazed how well it idles and sounds after I did the color tune back then and a second carb sync.

Unfortunately, I haven't been able to ride it since due to the battery charging issue. And yeah, not having a working front brake is an additional concern...

 

Nice video! Nice bike, too!!!