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Hey guys, been busy working on the bike, started to mess with the jets but it ran so well after valve adjustment and a carb sync, I decided (due to plug color), to just wait a tad longer until the weather turns cold. I have everything to do a full Carbie rebuild, but im having too much fun riding it to work lately 😉. I've recently slapped a new seat cover on.. trimmed and tidied up the rear end, p.o. destroyed the rear fender anyway, swapped new shocks on back there as well. Serviced the front forks which made a world of difference in the brake dive.
 

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Which brings me to today's we question! I usually plug all my bikes into a battery tender when they are in the stable, this one included...I have recently just realized that this thing isn't charging when riding! Lol! But due to the nightly battery tender, it's been running fine😂. At 2k I only get about 12.6 on volt meter between battery terminals. Should be over 14v correct? Alt brushes look to be well within spec as well. Im about to start working my way through the manuals troubleshooting. Just curious in your guys opinion, what is the usual culprit on these 81's? Thanks in advance!
 
Which brings me to today's we question! I usually plug all my bikes into a battery tender when they are in the stable, this one included...I have recently just realized that this thing isn't charging when riding! Lol! But due to the nightly battery tender, it's been running fine😂. At 2k I only get about 12.6 on volt meter between battery terminals. Should be over 14v correct? Alt brushes look to be well within spec as well. Im about to start working my way through the manuals troubleshooting. Just curious in your guys opinion, what is the usual culprit on these 81's? Thanks in advance!
The usual culprit is the rotor, but they usually short and drain the battery in a few minutes. Perhaps yours is open? I had a voltage regular go low on my XS1100. I think it might be the same unit. It was still operating, but it would not give me 14 volts.
 
The usual culprit is the rotor, but they usually short and drain the battery in a few minutes. Perhaps yours is open? I had a voltage regular go low on my XS1100. I think it might be the same unit. It was still operating, but it would not give me 14 volts.
Great info! Thanks man!
 
Which brings me to today's we question! I usually plug all my bikes into a battery tender when they are in the stable, this one included...I have recently just realized that this thing isn't charging when riding! Lol! But due to the nightly battery tender, it's been running fine😂. At 2k I only get about 12.6 on volt meter between battery terminals. Should be over 14v correct? Alt brushes look to be well within spec as well. Im about to start working my way through the manuals troubleshooting. Just curious in your guys opinion, what is the usual culprit on these 81's? Thanks in advance!
The '81 has a combined reg/reg. It's pretty reliable. Usual culprits are the brushes and the rotor. If it's the rotor, I know a guy.... ;)
There's a troubleshooting guide in TECH. I copied it and added a few test items to it. Have a read here....

https://www.xs650.com/threads/rewound-alternator-rotor.54276/post-584935
 
The '81 has a combined reg/reg. It's pretty reliable. Usual culprits are the brushes and the rotor. If it's the rotor, I know a guy.... ;)
There's a troubleshooting guide in TECH. I copied it and added a few test items to it. Have a read here....

https://www.xs650.com/threads/rewound-alternator-rotor.54276/post-584935
That's a great troubleshooting guide! Much easier than the manual! After realizing and fixing the fact that my AutoZone fuseblock was only letting 10v through to the brushes, I moved on through the tests. Once I had full voltage at the brushes I moved onto the rotor tests only to discover a reading of 4.5ohms between the slip rings. According to the tech writeup, this would be a bad rotor? It never has snatched the feeler gauge yet either, I'm going to borrow a better meter from work tonight and re-check my work but Im leaning towards a bad rotor right now. Probably caused by the low voltage to the brushes?
 
Yes, 4.5Ω's is on the low side, but that should be high enough to charge. Maybe not a good charge, but at least 13v when rev'd. It's quiet possible the resistance is dropping (shorting) while it heats up in operation... in which case yeah, it's bad.
Did you try grounding the green wire at the brush and see if the rotor passed the "slap" test? Or if the charge voltage went up at the battery?
 
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Yes, 4.5Ω's is on the low side, but that should be high enough to charge. Maybe not a good charge, but at least 13v when rev'd. It's quiet possible the resistance is dropping (shorting) while it heats up in operation... in which case yeah, it's bad.
Did you try grounding the green wire at the brush and see if the rotor passed the "slap" test? Or if the charge voltage went up at the battery?
I have a rewound rotor on Miss June (I guess I can call it that). It has been spinning in my alternator for about 20 years. I don’t remember its resistance, but I thought it was under 4 ohms. I remember a low number from when I bought it. It works just fine.
 
I have a rewound rotor on Miss June (I guess I can call it that). It has been spinning in my alternator for about 20 years. I don’t remember its resistance, but I thought it was under 4 ohms. I remember a low number from when I bought it. It works just fine.
The problem is if it's an OEM rotor it should be 5.2Ω. 4.5Ω kinda suggests the insulation is breaking down. That's why I wondered if it was dropping when it gets hot.
If it's rewound to 4Ω with new wire, it'll charge just fine, as you say.
 
The problem is if it's an OEM rotor it should be 5.2Ω. 4.5Ω kinda suggests the insulation is breaking down. That's why I wondered if it was dropping when it gets hot.
If it's rewound to 4Ω with new wire, it'll charge just fine, as you say.
You’re right. I wasn’t seeing it your way.
 
Yes, 4.5Ω's is on the low side, but that should be high enough to charge. Maybe not a good charge, but at least 13v when rev'd. It's quiet possible the resistance is dropping (shorting) while it heats up in operation... in which case yeah, it's bad.
Did you try grounding the green wire at the brush and see if the rotor passed the "slap" test? Or if the charge voltage went up at the battery?
Ya Jim, I did try the green wire jumper while revving to 3k, only about 12.8 at the battery, and it also failed the slap test while jumpered.
 
Boss sentenced me to the nightshift for the week😵‍💫, I'll retest with a better meter when I get some more shop time.
 
Had a spare hour before work, curiosity got the best of me. I removed the rotor off the 80' (this one had a good ohm read), and installed it on the 81'. Still fails the slap test, but this time, for some reason, I am only getting about 11.38v at the brown brush lead🤔. The hunt continues...
 
You've got 2 connectors... the engine (rotor & stator) disconnect and the reg/rec disconnect. If you haven't already done so, clean those pins real good.
Best cleaning you can do is remove the pins (one at a time) and scrub 'em real good with a small stainless wire brush.
 
You've got 2 connectors... the engine (rotor & stator) disconnect and the reg/rec disconnect. If you haven't already done so, clean those pins real good.
Best cleaning you can do is remove the pins (one at a time) and scrub 'em real good with a small stainless wire brush.
Thanks Jim, that'll be my next move.
 
I traced the poor voltage at the brushes down to a connector at the fuse block. Replaced one connector setup mentioned by Jim as it was terrible, de-pinned and cleaned the other. Still failing the slap test and no charging volts at 3k. Moved onto the stator check, checked the three possible white wire combinations with the engine idling and couldn't get more that 0.5V AC...problem with the stator?
 
I traced the poor voltage at the brushes down to a connector at the fuse block. Replaced one connector setup mentioned by Jim as it was terrible, de-pinned and cleaned the other. Still failing the slap test and no charging volts at 3k. Moved onto the stator check, checked the three possible white wire combinations with the engine idling and couldn't get more that 0.5V AC...problem with the stator?
Too early to say. Correct stator output requires everything else working. For instance, a broke wire at a brush means no output at the stator. Not the stators fault though... means the rotor isn't being energized.

Still failing the slap test means the rotor isn't energizing. Don't take this wrong, but I'd suggest you start over from scratch.... maybe with pics or videos as you go.

Fwiw, the stator is as close to bulletproof as you can get. I'd wager it's just fine.
 
Too early to say. Correct stator output requires everything else working. For instance, a broke wire at a brush means no output at the stator. Not the stators fault though... means the rotor isn't being energized.

Still failing the slap test means the rotor isn't energizing. Don't take this wrong, but I'd suggest you start over from scratch.... maybe with pics or videos as you go.

Fwiw, the stator is as close to bulletproof as you can get. I'd wager it's just fine.
OK, makes sense. I'll start the the troubleshooting from scratch again. And I'll try to include some pics.
 
Ok guys, lemme start by saying I've cleaned or replaced most of the connectors here, I know the frame looks cruddy but the connections are good here. So before starting from scratch, I wanted to check the other brush lead for voltage, and believe it or not I've had two energized brush leads. So that had me to thinking a problem with the green wire. So I jumpered directly to the battery negative and bingo! Pulls the feeler gauge right to the case! I then started the bike, gave it a rev and charging Volts grew ever higher with the revs,.even saw up around 18vdc😬....so, now, I'm cautiously optimistic that my regulator, or it's ground has failed?!? If so, can I slap the 80's reg in this '81?
 

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