Do I have a bad Stator?

My bike is a 1981 XJ650 Maxim. Today I was checking the output of the charging system with a VOM and measured a constant 12v with the engine idling anywhere between 1000 rpm to 2000 rpm. Once or twice I measured 15v at 2000 rpm. I then disconnected the alternator harness and performed a resistance check. I measured 17.5 ohms across the two field coil leads (the green wire and the brown wire). I then checked the resistance between the three white wires and measured 2 ohms. According to the Haynes shop manual, the resistance across the field coil leads should measure 4 ohms and the resistance between any of the three white wires should measure 0.46 ohms. This is probably a stupid question but I am going to ask it anyway. Is this enough evidence that the stator is bad? Also, how hard is it to remove the stator?

 

out of spec is a sign of being bad....

Note that worn, dirty, or damaged alternator brushes can affect these readings, as can "dirty" copper commutator rings on the rotor face (where the brushes contact the rotor):

quote from this link
http://www.xjbikes.com/forums/threads/the-ultimate-relay-switch-sensor-and-diodes-guide.27543/

info near bottom pf page

Brushes are 17mm long - spec is at least 12.
quoted from link in the link above.
this is the link

http://xjbikes.com/forums/threads/update-help-electrical-gremlins-strike-again.27387/

you got some reading to do, you may just have to clean a few things

 

I'd check regulator first..... Swap another in and retest.

 

That is definitely not the problem. In fact the brushes and slip ring were one of the first things I checked.

 

The voltage regulator is brand new. I replaced it thinking that it was the problem. Apparently it wasn't the problem. Battery is good with a full charge.
The charging system is not putting out the specified 14.4v @ 2000 rpms's.

 

if youREADthe links i posted what it tells you is before doing major work to make sure all connectors and contacts are clean as this will affect your readings.
so if you have done that then you need a new alternator setup as both readings tested out of spec.

 

Measuring 2 ohms could be a problem. Did you check your meter by shorting the two leads together to be sure you get very close to zero ohms? It is a fairly simple procedure to change the stator if needed - 3 bolts and a gasket and some wire routing that is a bit of a pain.

Do you have a service manual? There is a detailed procedure for testing the charging system that is quite good with the exception that the V1 and V2 voltages are labeled incorrectly in some of the manuals.

What kind of voltage do you have on the green wire with the bike not running? Should get 1 to 1.8V, which is a good indication the field coil excitation is correct. On a working system the green wire should go positive to around 9 to 11V with the bike running and the RPM raised to around 2K. The brown wire at the regulator, which receives power from the signal circuit should be close to battery voltage.

 

what does the bike do or not do that led you to test it?

 

I agree

 

The battery was not being charged during a ride. If I were to stop for gas and shut the engine off, I would have a heck of a time getting the engine to fire back up. The starter wouldn't spin fast enough to effect the starter clutch to engage. It would chatter something awful. On two occasions I finally got the engine to fire back up (something short of a miracle). When I got home I'd hook up the battery to a maintainer and it would charge for about 15 minutes until it indicated that it was charged. This was a fairly new battery too. I decided to check the electrolyte and two of the cells were on their way out.

 

Thank you Rooster 53. I'm going to post an update. I just came in from the garage and have some good news (I think).

 

All, Here's an update on my charging system diagnostics. First and foremost let me say this: never trust a Harbor Freight digital multimeter. This is what I was using before my initial post (shame on me for being lazy) and it got me in trouble. Tonight I pulled off the alternator cover to measure the field resistance across the slip rings on the rotor. I was using the Harbor Freight meter and was measuring 6.7 ohms. Then I decided to do a continuity check on the two wires that run from the brushes to the regulator. I was measuring 1.5 ohms per wire. By now I was getting suspicious. I touched the two meter probes together and the display showed something like 2.7 ohms. I am embarrassed to admit that I was using this junk to perform my diagnostics. I went and got out my Sears Craftsman analog VOM, which I should have done all along. I set it to the 1x ohms scale, zeroed it in and rechecked the field coil and stator. Here's what I came up with: 4.1 ohms across the rotor slip rings (field windings); 0.5 ohms between all three of the stator windings The rotor slip rings were clean (nice and bright). As for the wires that run from the brushes to the regulator - they measured zero ohms. Now for the brushes. The brushes measure .550" long (13.97mm). That makes them .118" (3mm) shorter than spec (17mm). Is it possible that the brushes have been my issue all along? I'm going to go ahead and replace them and see if things improve. To all who responded; thank you. P.S. I'm going to break down and buy a Fluke digital mutimeter. No more Harbor Freight junk for me.

 

All, Here's an update on my charging system diagnostics. First and foremost let me say this: never trust a Harbor Freight digital multimeter. This is what I was using before my initial post (shame on me for being lazy) and it got me in trouble. Tonight I pulled off the alternator cover to measure the field resistance across the slip rings on the rotor. I was using the Harbor Freight meter and was measuring 6.7 ohms. Then I decided to do a continuity check on the two wires that run from the brushes to the regulator. I was measuring 1.5 ohms per wire. By now I was getting suspicious. I touched the two meter probes together and the display showed something like 2.7 ohms. I am embarrassed to admit that I was using this junk to perform my diagnostics. I went and got out my Sears Craftsman analog VOM, which I should have done all along. I set it to the 1x ohms scale, zeroed it in and rechecked the field coil and stator. Here's what I came up with: 4.1 ohms across the rotor slip rings (field windings); 0.5 ohms between all three of the stator windings The rotor slip rings were clean (nice and bright). As for the wires that run from the brushes to the regulator - they measured zero ohms. Now for the brushes. The brushes measure .550" long (13.97mm). That makes them .118" (3mm) shorter than spec (17mm). Is it possible that the brushes have been my issue all along? I'm going to go ahead and replace them and see if things improve. To all who responded; thank you. P.S. I'm going to break down and buy a Fluke digital mutimeter. No more Harbor Freight junk for me.

 

yup you need new brushes. maybe?

now for some free advice.
if you doubt a measuring device test it against a known good measurement, voltage of battery (D Cell 9 volt battery) resistors pick up a few at radio shack in the ranges you will be testing.

when you have a system that is not working as it should the first thing you should check is the wear parts. Check then carefully and methodically.
in you case check battery and charging voltage which points to the possible problem.
high voltage voltage rectifier low voltage alternator.
voltage regulator requires a connector check clean and shiney then a diode test .
alternator: check connectors, copper commutator rings (contact point) again check clean and shiney and brushes , the wear items.

you were ready to buy a new stator because you did not check the brushes.
be slow and methodical, you will save money.

if you have a front brake problem check sight glass for fluid lever if low ask why, possible answer leaks or its in the caliper because the pads are worn.
check pads and use a measuring device in spec fil MC and bleed brakes the look for a leak.
McRepairs and guessing ain't the way to go.

when you ask questions Listen to the answers as if you have not already drawn a conclusion to the problem

sorry if I come across as harsh,
and advice is free you do not have to take it

 

you may want to test the charging system with your new meter see if it makes a differance.
sounds more of a battery issue than alternator issue with your post above. you can add distilled water to the battery to see if it comes back to life.
charge it up overnight and do a start test on it to see how low the voltage goes when trying to start it.
after all your brushes are in spec. 12 mm replace 17 mm new
brushes are cheap enough i would plan on replacing them before the next riding season anyways

 

I have also been checking out my charging systems.

Check voltage at 2000 rpm is 14.4 volts. voltage at 2500 rpm is 14.4 volts. resistance of rotor is 20 ohms (green and brown). resistance of the coil thing (3 white wires) is 0.8 ohms

 

read my first post in this thread and the 2 links you may just have to clean your connectors and copper commutator rings use a soft eraser for rings.
clean and measure length of brushes too. your voltage is ok . how old is your battery clean its connectors. battery fluid between lines? use distilled water to top off.
possibly change the batteries in your meter or borrow another meter if suggested cleaning does not work

starting your own post is a good idea if you still have problems . digital multi meter?