Suzuki 2 Strokes

Are there any special instructions for removing and replacing the rotor on a GT380 alternator? I thought I read something (somewhere) about a special puller being needed?

Second--are these rotors prone to failure? The one on my bike is like 6.5 ohms between the slip rings (with the carbon brush assembly completely removed) and the spare one I have is not much better at like 6.9 ohms between the rings.

Would a reading this low (manual says 10-12ish) cause a COMPLETE lack of charging, or would it just be low output?

Thanks,

Mike

Rotor coil should be 2-6 ohms.
If you'd like a copy of a service manual FOC, PM me your email addy.
Favourite for poor charging is bad wiring between battery and regulator.
ALL connections MUST be good - including earths.

Try a new battery in your tester - a failing battery will give high readings.

Keep in mind that the specs were written for testing equipment from back then.

See page 15 of this for the spec: http://www.ozebook.com/compendium/suzi/suzidata1.htm
2 — 5 ohms is for Kokusan alternators & 10 — 20 ohms is for Nippon Denso alternators.

The GT380 shop manual is here: https://www.oldjapanesebikes.com/mraxl_ ... /index.php

I’ve had bad rectifiers. The voltage regulator is mechanical and may need servicing/adjusting.

Wiring problems between the battery - ignition switch - alternator can cause too big of a voltage drop.
This could cause poor charging because not enough current can be delivered to the rotor.
This could also cause overcharging because the voltage regulator is adjusting for the voltage its being provided. (The voltage regulator doesn’t the actual battery voltage.)

What problems are you having?

I have the Nippon-Denso unit (both) and they are both around 6.5 ohms when testing the slip rings.

Brand new (modern) regulator/rectifier unit installed. all new wiring with clean grounds and connections.

I'm getting only battery voltage at the battery (12.8 fully charged on a new battery) and not seeing the usual 13.5 - 14.5 from idle up past 2k rpm. So essentially I'm getting nothing from the alternator.

The quick Ohm check on the rotor is the eye-opener right now in that its coming back way under the low end of the spec.

What is your history with this bike? Did you ever have a good working alternator?

Suzuki had a design problem with Nippon Denso rotors on the early GT380/GT550/GT750.
They modified the rotor assembly to fix the problem.
To visually check to see if you have early rotors see: http://www.ozebook.com/compendium/techb ... mpress.pdf


Perhaps another forum member with a good Nippon/Denso alternator on a GT380/GT550 might know what their rotor resistance is.

Providing that you have continuity between the two slip rings, it's a pretty safe bet that the problem is NOT the rotor.

Don't forget that Suzuki in its infinite wisdom decided to over-complicate the charging system by using an excited-field alternator. As long as the rotor passes current, it will generate the magnetic field that it's supposed to do. So I suspect the problem is either in the wiring from the battery down to the rotor brushes, or in the stator / the wiring to the new reg-rec.

I would check the voltages from the battery down to the 'live' rotor brush. If that all checks out and you've got battery voltage going into the rotor, great. Then you need to check the continuity of the stator yellow wires, to see if the reg/rec is actually receiving any current from the stator.

Hi Craig,

Thanks for the reply. I just checked voltage at the live brush with the battery ON and I'm getting 0 volts...

Is there a (somewhat safe) way to check AC output of the alternator while the bike is running (before the regulator/rectifier) just to confirm I'm getting output?

I re-checked my wiring and I don't see anything glaring, I supposed I'll run it again today and see if I can come up with anything.

What is the best way to check the stator? I originally followed the repair manual steps but looking back now they are vague at best and don't give anything exact to work with.

Same with the Regulator/Rectifier.

Thanks,

miked914 wrote:Hi Craig,
Thanks for the reply. I just checked voltage at the live brush with the battery ON and I'm getting 0 volts...

Is there a (somewhat safe) way to check AC output of the alternator while the bike is running (before the regulator/rectifier) just to confirm I'm getting output?

I re-checked my wiring and I don't see anything glaring, I supposed I'll run it again today and see if I can come up with anything.

Yep, if you've got no battery power to the brushes, the rotor will not generate a field and you'll get nothing from the alternator. The rotor has very, very little magnetism without an input voltage - certainly not enough to generate anything from the stator.

From memory, the 'live' wire carrying battery voltage to the brushes from the regulator should be green. Are you getting 12V on the green wire where it attaches to the brushes?

If YES, there's a fault in the internal brush assembly connections.

If NO, then the fault is upstream in the wiring harness. The original regulator only has three wires: green to the brushes; orange, which connects to the orange&white wire which serves the ignition coils and killswitch; and black&white which is your earth or ground.

Now, a 380 will run for 50+ miles on a good, freshly-charged battery (lights OFF, of course) even when running total-loss electrics. If the bike will start and run in this way, and the kill switch works, then that pretty much rules a problem in THAT side of the loom.

I would double-double check the wiring of the new reg-rec unit that is fitted.

Check your spare stator to see if its the early one that Suzuki had troubles with.
For method to check see: http://www.ozebook.com/compendium/techb ... mpress.pdf

See “Engine Electrical “ in the shop manual: https://www.oldjapanesebikes.com/mraxl_ ... /index.php
It has a method for an isolated check of the rotor+stator.
1) disconnect the rectifier/regulator so that the rotor+stator is isolated.
2) run a temporary wire from the battery + to the alternator green wire. Only connect it during the test.
3) check the AC voltage between each combination of yellow alternator wires at 1.5k & 2.5k rpm.
4) disconnect your temporary wire as soon as the test is done so that the rotor doesn’t overheat.

The test in the manual is a little different because it includes the rectifier.

Which rectifier/regulator brand & model are you using?

OK--so I've got it all pulled apart and here is what I know.

My green "brushes" wire from the alternator to where it plugs into the regulator/rectifier is showing clean continuity from the connector end to the brush assembly, so no breaks in the wiring. I'm getting 0 volts at the green wire at either end though. I am getting 12.8 (battery voltage) at the white/yellow wire that plugs into the regulator/rec though.

Strong voltage at the red input wire into the Regulator/Rec but 0 voltage coming out of the Reg/Rec on either the Black, Orange or Green wires.

Should I be getting voltage coming out of the Reg/Rec? Seems that at least the green should be showing voltage in order to feed it back downstream to my alternator brush.

Grounds are good to the Reg/Rec and again, voltage is getting IN as part of the Red input and 3 Yellow from the stator.

Oh, and the bike does run and start just fine. I put 20 miles on it and never noticed an issue. I'm only running an LED tail light strip and LED headlight, nothing else so there is very little voltage draw.

Which rectifier/regulator brand & model are you using?

an Ebay combo unit--generic manufacturer. Seems to spec out OK when I checked it this afternoon.

I asked so that I could confirm that you got the correct R/R. In the past, after considerable posting we found out that the person had gotten the wrong R/R.

Another common problem is grounds. For example, a member gets the frame powder coated. Then the ground they’ve selected for the R/R is insulated by the powder coat.


With the R/R connected up & the bike on but not running, what is the voltage of the green rotor wire at the connector to the R/R?