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Stator Testing Question - '77 GS750

  • Thread starter Thread starter TONY.STEWART
  • Start date Start date
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TONY.STEWART

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I have a question related to testing the stator on my GS750. I have read the stator pages and specifically have a question related to the fault finding flow chart. During test phase B we disconnect the stator wires and measure the resistance between the stator leads. If readings are between .5 and 2.0 OHMs we then check the connection to the casing. If all is ok here we are then asked to check AC voltage between the stator leads with the engine running at 5000 RPMs. This is where my question arises. My Clymer manual makes the following statement in the section where we test the rectifier:

Do not run the engine with the rectifier leads disconnected: the alternator is certain to be damaged.

My question is, if the stator is disconnected as suggested, will it damage the alternator (stator)?

Just wanted to get some input on this one before I fried anything. Thanks
 
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Disconnect the terminal block from the stator. You can then measure the no load AC voltage which should be around 75VAC or so @ 5000RPM. Make sure you have the meter on the right range or you risk damaging it AND the stator!!
 
Measure them from post to post, wire 'A' to wire 'B', 'A' to 'C', 'B' to 'A' and 'C', etc. should get around 50 volts AC. more importantly is that they all produce around the same voltage. if on leg is low, chunk that puppy, because that stator is gone!
 
It will not hurt it to disconnect the stator wires. IF the stator is connected a bad reg could affect your readings.
 
OK... here's the latest. I have conducted all tests through test phase "B". Everything goes ok until I test the AC voltage between the leads on the stator. In all cases, I achieve only approximately 15 volts at 5,000 RPM. This is using a brand new stator. I have been trying to correct charging problems with this bike since I purchased it about three months ago. To date I have installed a new Electrosport rectifier, tried three different voltage regulators (one from a GS750 I have that charges properly), replaced the main wiring harness (more to improve the bike's electrical system as a whole) and switched the rotor from the same GS750 that I borrowed the good regulator from. Battery was new when the bike was purchased, holds a charge fine (unless I ride the bike, which discharges the battery) and electrolyte levels are fine. The original stator that I removed indicates about 1 ohm resistance between any two leads as does the new one that I installed. Don't know what the voltage was between the leads on the old stator. Didn't test it before it was removed. I understand that the test indicates that my stator is bad but I'm just a little skeptical because: a) it is brand new and b) I get the same low (15 vac) reading between any two leads.

Any thoughts?
 
Just had an accidental discovery... found out there are both Kokusan and Nippondenso stators... Could it be that I purchased the incorrect stator? Would either bolt up correctly but require the appropriate rotor to function properly? Don't know about the stator I put in, but the rotors I've tried both have 14mm x 1.5 internal threads (for pulling the rotor). The puller I purchased from Dennis Kirk for the GS750 came with 16mm x 1.5 threads and I was unable to use it. Do the Kokusan and ND rotors have different internal threads. Just trying to figure out if there's an easy way to know which rotor I have (if there are indeed two different styles?!). Anyone out there with any input?
 
You are completely correct about the two different manufacturers used for the stators on the early GS's.

I don't know all that much about it, but I believe one was used for the 77's and some of the early 78 models, and then it was switched to the other and kept that way for the remainder of the GS series production (and still probably their sole supplier to this day). So chances are if your stator is from a late 78 model or later, yes, the stator is probably different. And to the best of my knowledge they are NOT interchangeable. Don't quote me on this, but I seem to remember hearing that one has much more closely wound and more plentiful windings than the other.

Do you have any salvage shops nearby? They would probably be able to give you a heck of a lot better answer than I just gave, but I hope it helps a little!
 
Follow up

Follow up

Just wanted to follow up for any who are or will in the future be reading this thread. Removed the new stator I put in. Compared it to the original... Very different. The original is a Nippon-Denso with the familiar ND logo stamped in it. The new one I bought from Suzuki had no identification markings that I readily noticed but I'm sure it must be the Kokusan. The ND stator has 12 coils and the Kokusan has 18. I reinstalled the original ND stator, tested the voltage between the leads and got over 60 VAC before I even reached 4,000 rpms in each position. All readings were consistent. I connected the stator leads back into the harness and set my voltmeter to VDC. I connected the voltmeter leads to the battery, fired up the bike and watched the voltage steadily climb out of the twelves and well into the thirteens before I was satisfied and killed the bike.

So I'm not sure what caused the original charging problem. I've replaced the voltage regulator, rectifier and most of the factory wiring. I also ran grounds directly from the negative battery terminal to the rectifier and regulator. All connections are squeaky clean and are coated in dielectric grease for corrosion resistance.

Glad to have put the electrical gremlins to rest so that I can move on to other parts of the project! Thanks for the help.
 
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