850T-3 Not Charging

[Piston Broke]

Greetings! During my first ride this year, my '76 T-3 died due to the battery not charging. Unfortunately I have never been good with electronics, my brain just doesn't work that way i guess. Anyway, I could use some help troubleshooting the issue. Thank You!!
She ran quite well last year...
The battery light stays on while the engine is running which indicates an issue.
I measured 4 volts at the screws where the alternator brushes attach while running.
There is no continuity between the two rings when the brushes are lifted up.
How do I test the regulator? How could it possibly go bad during the winter?








 

[moto-uno]

  It seems you have a common high mileage charging problem and you've already found the problem .
No continuity between the rotor rings means the winding in the rotor is broken and no magnetic field can be produced .
It is a single wire that is wound around the rotor and each end comes out to it's own rotor ring .
I've had some entertaining time rewinding a couple of my own  .

[guzzisteve]

The best trouble guide is in the 1000SP/G-5 service manual- I would read it

[moto-uno]

  ^ Or start with a rebuilt or new rotor .

[wirespokes]

  It seems you have a common high mileage charging problem and you've already found the problem .
No continuity between the rotor rings means the winding in the rotor is broken and no magnetic field can be produced .
It is a single wire that is wound around the rotor and each end comes out to it's own rotor ring .
I've had some entertaining time rewinding a couple of my own  .

I'd be interested in your rewinding adventure. I never thought of rewinding any of mine that failed, thinking it was beyond my abilities. But thinking of it now, the only real problem is baking the epoxy. That, and maybe removing the epoxy to get at the wires.

My understanding is that most of the failures are where the wire connects to the slip ring. The winding starts loosening up from hard acceleration/deceleration working the connection till it breaks.

[Antietam Classic Cycle]

New rotor:
https://www.euromotoelectrics.com/product-p/boalt-rotor642oe.htm
https://www.mgcycle.com/index.php?main_page=product_info&cPath=37_161&products_id=760
https://www.crustycycle.com/products/copy-of-moto-guzzi-bosch-alternator-brush-holder-17712452-t3-convert-le-mans-bmw

This is a worthwhile upgrade while you're in there:
https://www.euromotoelectrics.com/product-p/vr-extadj.htm
https://www.mgcycle.com/index.php?main_page=product_info&cPath=37_161&products_id=1110

[n3303j]

A few things just don't add up here. First if you measure more than an a few ohms between the slip rings (brushes pulled clear) then the rotor is open circuit and failed. But you said the charge light stayed on while the engine was running and the charge light is used as a limiting resistor to apply initial current to the rotor. If the rotor is open circuit the charge light has no source of continuity and will not light. So no red light at cruise could mean all is well or your rotor or your brushes are toast. That is the reason that at 125K miles after being bitten in the butt by my second rotor I installed a voltmeter. Now I know if my system even hiccups.
But if it were my bike I'd clean and tighten every connection in the circuit. There's a few at the regulator, more at the diode board, a bunch more at the alternator, one at the key. And check all the ground paths. There is the main negative cable, a wire from frame to headlight shell and another one from diode board to frame. Connections can get a bit wonky after 50 years.  That's why I installed a Bender harness last winter.

[John A]

It isn’t causing the problem but when you put it back together the stator should be clocked so that the brushes contact the rotor from the side rather than from the top so the brushes are less likely to bounce and cause a low charging rate on rough roads. They put out a service bulletin on it.

[moto-uno]

  Concerning rewinding the rotor , getting the 2 outer flange pieces off is a bitch , they are pressed onto the splined main-shaft with an extreme interference fit .
Once those are off the entire winding pulls off . The wire wrap and shellac (and wire) were available from an electronics store here in Vancouver (Lee's Electronics)
I originally started with 22 gauge wire , ended up at 19 gauge which gave me ~3.4 ohms , the correct reading and it charged well with the lights off , not enough with lights on.
That's when I realized that although I'd wound it well , I hadn't built up the base of the main-shaft enough with the wrap to locate the coils closer to the flanges .
After doing this 3x , spring arrived and I put off the next one waiting for a few rainy days .
The supplied shellac was heat resistant and kept all the wire windings in place.
And to simplify the charging wiring , get rid of everything except for the 3 rectifier leads and the +ve lead from the regulator and add a voltmeter(as suggested earlier) and be done
with all that other crap that can add it's own special problems , has served me well for decades on my LeMans2 .

[n3303j]

Looking hard at the pictures (nice detail) I'd take everything apart and clean it thoroughly. If the rotor truly measures infinity then replace it. The brushes seem to be sitting a bit low in the holders. Best time as any to solder in new ones. And I'd be really suspect that dampness has gotten into the regulator and put it out of service. MG Cycle stocks a solid state one for about $25. Don't bother with adjustable as the potentiometer is just a spot for water intrusion. The fixed one outputs 14.4 VDC which is good for any battery the T3 likes. The fixed one is fully potted and as a bonus takes less space in the same mount. Lasts forever (or 100K miles, whichever comes first).

[Dukedesmo]

The Rotor windings on my LM2 failed last year, basically the wire in the winding broke, when working there should be around 4 Ohms resistance between the slip rings.


I'm told it's quite common on this type of alternator which, BTW is also used on BMW twins, making them more widespread than if just used on Guzzis.



I got mine rewound by a company that specialise in rewinding motorcycle systems (West Country Windings, UK), they turned it around in about a week and it is now working fine.


As they have been repairing these for a long time and have improved the method, they tell me that the repair they make is stronger than the original.

[Tkelly]

I replaced a diode board on a t3 and an airhead,solved the problem.

[Piston Broke]

I am absolutely overwhelmed by your responses, THANK YOU!! I think I'll go with the new rotor and regulator route. Every couple years she needs a little extra lovin'. I would eventually like to install a Greg Bender wire harness and replace the fuse box, a daunting task given my lack of proficiency. Thanks a bunch to all of you!

[Dave Swanson]

I am absolutely overwhelmed by your responses, THANK YOU!! I think I'll go with the new rotor and regulator route. Every couple years she needs a little extra lovin'. I would eventually like to install a Greg Bender wire harness and replace the fuse box, a daunting task given my lack of proficiency. Thanks a bunch to all of you!

An electrical Luddite like myself has no issues installing a GB wiring harness.  There is also extensive blow by blow instructions with many pictures on his site.  He makes it so simple even a caveman can do it.  No fear.

[n3303j]

I am absolutely overwhelmed by your responses, THANK YOU!! I think I'll go with the new rotor and regulator route. Every couple years she needs a little extra lovin'. I would eventually like to install a Greg Bender wire harness and replace the fuse box, a daunting task given my lack of proficiency. Thanks a bunch to all of you!

Unless the fuse block is broken I'd keep it. I took my 50 year old unit off the bike, scrubbed it with Brasso, then Simple Green and finally finished  cleaning with lots of hot water and compressed air. The box is solid and well made. It is a good anchor for the fuses and the harness. There are jumpers at the back of the box that establish current paths. Finally the bottom two fuses are "freebies" as they aren't used on my '66 T3 factory stock wiring. So it is through there I installed heated grips, GPS and voltmeter.

[turboguzzi]

I'm told it's quite common on this type of alternator which, BTW is also used on BMW twins, making them more widespread than if just used on Guzzis.

just be aware that some BMW stators have a 107mm base circle, while guzzis are 105mm....

and if both stator and rotor are bad = $$$ , so time to think about a much more modern system with fixed magnet, like the electrex one

https://www.electrexworld.co.uk/cgi-bin/sh000001.pl?WD=guzzi&PN=STK%2D502%2Ehtml#SID=826

[Piston Broke]

I installed the new rotor but stopped short of installing the new voltage regulator because I have some more questions. Normally I'd go for it but once I pull the current regulator, re-installing it will be twice as difficult. My question is, my current regulator appears to have a rubber boot around a plug, is that just a dust cover and if it's a molded plug, is that compatable with my new regulator?

[n3303j]

Seems the plug layout is pretty universal. The original termination matches the new potted solid state unit.

[wirespokes]

Yes, that voltage regulator will work, but I think you found the problem was the rotor. If the rotor has no continuity between the slip rings, it's toast.

  Concerning rewinding the rotor , getting the 2 outer flange pieces off is a bitch , they are pressed onto the splined main-shaft with an extreme interference fit .

How did you separate the two halves?

[chuck peterson]

A second ground wire from the diode board to the engine case can be helpful when you put it back together

[Piston Broke]

Well, dang! I installed the new rotor and new voltage regulator. The battery charge light was still illuminated during a test run indicating the battery is not charging. What should I check next? I live in Grand Rapids, MI. if anyone is nearby.

[Tkelly]

Jamie Muller is still around Grand Rapids,did you install a new rectifier?

[michaell32]

Looks like on your bike the rectifier and regulator are two separate units.  Your rectifier may be bad.

[BRG-BIRD]

Make sure your grounds are good

[Dukedesmo]

I had the rotor rewound on my LM2 last year.


Just a couple of weeks ago, on a rideout it stopped charging, charge light on, luckily only a couple of miles from home so no breakdown.


I checked everything and all seemed OK, rotor still good with 4 ohm between the slip rings but of course once it had cooled down I couldn't get it to replicate the fault but in checking the wiring to the alternator, I found that the connections to the brushes are;


1. 12v +
2. 12v - but there was no actual wire connected to the tab, rather it relies on the ground passing through the body of the alternator which 'could' be getting a bad connection?


Now I'm not certain that this is the problem but I have had ground problems before, notably with the rear indicators that take the - from ground through the stalks/rear frame, that were not always working and adding a separate wire from battery - to bulb solved it.


So I have now added a wire direct from the tab on the brush to the battery - to eliminate this as the possible cause and it tests out OK though I haven't actually ridden it yet so there could still be a fault somewhere on the reg/rec - after all it is nearly half a century old.     

[n3303j]

If you completely remove the diode board from the bike you can:
1. Give it a complete scrub down in hot soapy water to remove all accumulated debris. Dry well.
2. Polish all contacts and grounding points to assure low resistance connections. I seem to remember board has grounding contacts to its metal heat sink frame for grounding. Those contact areas must be clean.
3. Grab your multimeter, set it to diode check, and check EVERY DIODE ON THE BOARD. There are only diodes. Big ones and small ones. Every one MUST be conductive in one direction and resistant in the opposite! If so, your board is good.
4. Check that all spade connectors are clean and tight.
5. Reassemble and try again.

Simple enough, just eats up a bit of time. But once every 10 years should be sufficient.

[Piston Broke]

I have a new diode board coming in the mail. More news to come!

[n3303j]

I have a new diode board coming in the mail. More news to come!

Is the old one bad?

[moto-uno]

  Concerning pulling the flanges off the shaft , I used an enormous 2 armed puller and eventually had to use a dremel to cut some reliefs between
the shaft and flanges , I suspect in time I'll make a puller that pulls on all the flanges at once , next winter !

[Piston Broke]

Is the old one bad?

l have no idea how to test it, I don't know what it is for.