GT550A - Alternator Failure?

All to do with wiring, charging or just trying to figure out whats gone wrong.

Moderators: oldjapanesebikes, H2RICK, diamondj, Suzsmokeyallan

Post Reply
texranger
On the street
Posts: 12
Joined: Mon Mar 22, 2021 12:46 pm
Country: United States
Suzuki 2-Strokes: 1973 & 1976 GT550
Location: Conroe, Texas

GT550A - Alternator Failure?

Post by texranger »

Howdy folks, it's my turn to ask for some guidance. I was riding my lovely GT550A a few weeks ago when all of a sudden she died. I pulled up, kicked it multiple times and nothing. After waiting 10 minutes or so I kicked it again and she started but only ran for about 30 seconds. Fortunately I was not too far from home so I called the wife and she came to the rescue. Hooked up the booster cables from truck to GT and after a few minutes the battery had charged enough to allow me ride her back home.

Note: I'm aware that the starter clutch gear is not in good condition/damaged so I don't use the push button start the bike; I have the parts to replace it but need to find time to do it.

I wasn't not able to do anything until yesterday so I recharged the battery and got to play with it. I do have a nice Fluke RMS multimeter and know how to use it. Started the bike with a freshly charged battery at 13.3V and it went down to 12.7V after about 45 seconds of running. It continued to drop to 12.5V until I shut it off. I checked the rectifier and regulator per the instructions in the manual and I believe that those 2 components are good.
The battery is about 6 months old (was told by previous owner).

So, I recharged the battery and a couple hours later I was ready for another test. Unplugged the stator connector, started the bike and I'm only getting 1.3V AC @ 5000rmp (only 0.6V AC at 2500-3000rmps) on all 3 yellow conductors at the plug.

Pulled the alternator cover and checked the carbon brushes; both of them not cracked/broken and measuring about 7mm. Checked alternator rotor resistance and I get only 4.5-4.7ohms. (Nippon Denso and manual says it should be between 10-20 ohms).

Is this enough evidence to indicate that my alternator rotor or stator are toasted?

Thanks in advance!! - Nic
User avatar
Alan H
Moto GP
Posts: 3160
Joined: Thu Feb 16, 2012 11:50 am
Country: England
Suzuki 2-Strokes: 4 x GT550s - J, M, A, B.
Location: The Republic of South Yorkshire

Re: GT550A - Alternator Failure?

Post by Alan H »

No. I'll try to find links to alternator issues elsewhere.....
Hang on a bit!
Think of how stupid the average person is, then realise that half of them are more stupid than that.
User avatar
Alan H
Moto GP
Posts: 3160
Joined: Thu Feb 16, 2012 11:50 am
Country: England
Suzuki 2-Strokes: 4 x GT550s - J, M, A, B.
Location: The Republic of South Yorkshire

Re: GT550A - Alternator Failure?

Post by Alan H »

Herewigo - https://www.kettleclinic.co.uk/kcforum/ ... Alternator
Have a read there. If you fancy 'joining' - it's free btw - please post a quick intro of who and where you are and details of your biking experience!


Anyway, basically, all Suzy triples have a similar charging system. The regulator 'looks' at the battery voltage and if it's low, sends more amps to the rotor so the electromagnet is stronger and allows the alternator coils to give more power out to the rectifier and battery.
Simple eh?
Welllll, the main problem with 40 odd year old bikes is that electrical connections get poor and the regulator 'thinks' the battery voltage is low when it isn't, so excess power goes to the rectifier and battery, the battery 'boils' and loses it's fluid.
Or, the connections to the rotor are bad - or the carbon brushes wear - and it doesn't allow the alternator to work correctly.
So, check you have battery voltage (ignition and kill switch on) to the rotor first. If it's lower than 1 volt, clean everything from battery to ignition switch - via kill switch, to regulator and rotor. Then check rotor and brushes.
If you'd like a copy of the Suzy service manual FOC, pm me your email address and I'll send you a copy.
After that, you need to be sure all three phases from the alternater to the rectifier are ok and then the volts from the rectifier to battery are ok.

You didn't expect this to be easy did you?
Don't worry, it's straightforward (honest!) and I'll help as much as I can.
How are you with wiring diagrams btw? It helps if I know that you understand what I'm telling you!!!
Oh, and make sure the battery is topped up first.
Think of how stupid the average person is, then realise that half of them are more stupid than that.
texranger
On the street
Posts: 12
Joined: Mon Mar 22, 2021 12:46 pm
Country: United States
Suzuki 2-Strokes: 1973 & 1976 GT550
Location: Conroe, Texas

Re: GT550A - Alternator Failure?

Post by texranger »

Thank you Alan! That was an interesting piece on the Clinic. I'm going to join!

It's actually pretty simple...it is just a matter of fully understanding it! - Ok, I just pulled the cover again, ignition and kill switch on and measured across the front rotor tracks. Result: 0.3V - Is that what I needed to check? If so, I'll start cleaning contacts points and report back.

Everything else, electrically related, works just fine.

And I'm pretty familiar with wiring diagrams, schematics, single-lines, etc. Should I consider getting a new battery, just in case?

Thanks again!
User avatar
Alan H
Moto GP
Posts: 3160
Joined: Thu Feb 16, 2012 11:50 am
Country: England
Suzuki 2-Strokes: 4 x GT550s - J, M, A, B.
Location: The Republic of South Yorkshire

Re: GT550A - Alternator Failure?

Post by Alan H »

Testing the rotor.
First check battery voltage and ensure there's enough liquid in each battery cell - top up with distilled water as required.
Lift the brushes and put a thin card between them and the tracks on the rotor, then on DC volts put red test wire on the top of the feed terminal (green wire iirc) and black on earth. That will give you feed voltage and it should be close to battery voltage (ignition and kill switch on). You can also check resistance in ohms across the tracks and from each track to earth.
See the KC thread for tests.
Then let the feed brush go back to the rotor and test from the second track to earth you'll get slightly less due to the resistance of the rotor. When you've done, take the last bit of card out!!
Remember that if the rotor wire is disconnected, then no power will go to it so it can't be an electro magnet and the alternator won't work.

Oh, and if you'd like a copy of the original service manual, drop me a pm with your email on, and I'll send a copy FOC. Tests are the same for all models.
Think of how stupid the average person is, then realise that half of them are more stupid than that.
User avatar
tz375
Moto GP
Posts: 6204
Joined: Mon Nov 03, 2008 10:47 am
Location: Illinois

Re: GT550A - Alternator Failure?

Post by tz375 »

To follow on from Alan's excellent advice, check the stator coils for resistance and the rotor and then check the rotor (field coils) power supply.

Under the side cover there's an electrical panel. What I'd check first is the power supply to the field coil with the ignition turned on. As Alan mentioned it should be 12v or so. He suggested checking that lead at the alternator end, which is the other way to do that. With power on, the regulator should be supplying 12V from the battery to excite the rotor. When the voltage gets over about 14v or so, the regulator opens its points and cuts off supply so teh generator stoops charging for a bit.

Regulator failure is common on these old bikes. The OEM unit can sometimes be cleaned up internally and made functional again, but many of us just replace them with a modern solid state unit.

The next most common cause of failure is corroded terminals in the connectors under that side cover. As they age and corrode, resistance rises and then they start to get hot and cause the plastic connector block to overheat. New connectors are available from SparckMoto for a nominal cost.
texranger
On the street
Posts: 12
Joined: Mon Mar 22, 2021 12:46 pm
Country: United States
Suzuki 2-Strokes: 1973 & 1976 GT550
Location: Conroe, Texas

Re: GT550A - Alternator Failure?

Post by texranger »

Gents,
I'm happy to report that I may have found the culprit of my problem (the main one...hope this didn't cause any other). When following Alan's testing procedure to test the rotor I noticed no DC reading at the feed terminal (Green wire). Nothing. I then unplugged the connector at the terminal panel just to check basic continuity between the plug and the ring terminal at the alternator. Nothing. Pulled the clutch/sprocket cover and found this...: (hint: chain)

So, I'll fix the wiring the best I can (splice & solder) and report back!

Thanks!
You do not have the required permissions to view the files attached to this post.
User avatar
Alan H
Moto GP
Posts: 3160
Joined: Thu Feb 16, 2012 11:50 am
Country: England
Suzuki 2-Strokes: 4 x GT550s - J, M, A, B.
Location: The Republic of South Yorkshire

Re: GT550A - Alternator Failure?

Post by Alan H »

Well, yes that could have something to do with it!!
There should be a small bracket to hold the cables away from the chain runs - item 9 on gt550 'electrical' here - https://alpha-sports.com/suzuki_parts.htm.
Think of how stupid the average person is, then realise that half of them are more stupid than that.
texranger
On the street
Posts: 12
Joined: Mon Mar 22, 2021 12:46 pm
Country: United States
Suzuki 2-Strokes: 1973 & 1976 GT550
Location: Conroe, Texas

Re: GT550A - Alternator Failure?

Post by texranger »

Alright...I'm a happy camper now! - Spliced and soldered the Green and Black/White-stripe wires, tucked and zip tied the cables away as much as possible and tested it. :up: She's charging! Getting 14.6VDC at 3000rpms.

Alan: there is a small bracket to keep the cables away from the chain. You can hardly see it in the second picture in between the chain; problem is it was not holding anything. It was fully "open", if you know what I mean. I made sure to "close" it holding the harness tight again the engine case.

Put it back together and took it for a spin around the neighborhood. They hate me already but I don't care. I truly enjoy riding my GT and all the right noises it makes!

BTW: i'm going to be looking into upgrading some of the electrical components (i.e.: regulator, rectifier and even some of the connectors) in the near future. This bike was supposedly restored/refreshed from the ground up but many of the original electrical parts were reused. Which is fine...to a point.

Thanks again for the help gents!
You do not have the required permissions to view the files attached to this post.
User avatar
Alan H
Moto GP
Posts: 3160
Joined: Thu Feb 16, 2012 11:50 am
Country: England
Suzuki 2-Strokes: 4 x GT550s - J, M, A, B.
Location: The Republic of South Yorkshire

Re: GT550A - Alternator Failure?

Post by Alan H »

Don't make the mistake of mending things that aren't broken. We've all been there.
I'll have to update my 550 threads - one nearly done (are they ever?) And t'other hopefully close too.
I got my 1st 550 in August 1972, 1st one private registered after the 'official' Suzuki GB ones. A 21st birthday present to myself which was 'breathed on' by Eddie Crooks and Frank Whiteway who were racing one in production 750 class at the time.
I still have the speeding tickets!!!
Think of how stupid the average person is, then realise that half of them are more stupid than that.
texranger
On the street
Posts: 12
Joined: Mon Mar 22, 2021 12:46 pm
Country: United States
Suzuki 2-Strokes: 1973 & 1976 GT550
Location: Conroe, Texas

Re: GT550A - Alternator Failure?

Post by texranger »

Wow..that's truly fantastic. (not the speeding tickets...well, heck those are good too!)

I'm not a believer in changing parts just because; if it's working, good. Stopped working, replace with similar or upgrade, if available. These last couple of days while "window shopping" for parts thinking there was a possibility I may need them, I realized there are not many electrical spare parts available..and if available, pricing is pretty ridiculous in some cases. So if and when they fail, if original is available, original is going back in. Otherwise, I hope to find a good, aftermarket replacement parts to keep it going.

Next up is the starter clutch! Oh boy..

Cheers and thanks for the help once again!
User avatar
Alan H
Moto GP
Posts: 3160
Joined: Thu Feb 16, 2012 11:50 am
Country: England
Suzuki 2-Strokes: 4 x GT550s - J, M, A, B.
Location: The Republic of South Yorkshire

Re: GT550A - Alternator Failure?

Post by Alan H »

texranger wrote: Fri May 21, 2021 11:50 am Otherwise, I hope to find a good, aftermarket replacement parts to keep it going.

Next up is the starter clutch! Oh boy..

Cheers and thanks for the help once again!
Plenty about - ask before you buy! And Starter clutches (borg warner - late type) are available on KC forum. I have one on each of my 550s.
Think of how stupid the average person is, then realise that half of them are more stupid than that.
User avatar
tz375
Moto GP
Posts: 6204
Joined: Mon Nov 03, 2008 10:47 am
Location: Illinois

Re: GT550A - Alternator Failure?

Post by tz375 »

That isn't as common as a regulator failure, but it is far more effective.

Glad you found and fixed it.
Post Reply