1977 GT750 Charging rotor.

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

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jabcb
Moto GP
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Suzuki 2-Strokes: 69 T350 thru 75 GT750
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Re: 1977 GT750 Charging rotor.

Post by jabcb »

Took a look at the parts diagram for GSXR750 -- that regulator/rectifier is not suitable for use on the GT750.

You got 15V @ 1.5k rpm on the test with a partially charged battery.
The spec is for >16V. Doesn't mention it, but that would be for a fully charged battery.

So it looks like your stator & rotor are ok.

Its worth checking the brushes since you have everything apart.
Also worth your time making sure the associated electrical connections are good & clean.

If it were me, I'd replace both the rectifier & regulator with modern parts from Oregon Motorcycle Parts. Their rectifier & regulator are direct replacements.

You could also upgrade to a modern regulator/rectifier, but you will have to figure out how to mount it.
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 & 75
GT380 72
T500 69 project & 73 project
T350 69 & 71
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE
ryder2shae
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Suzuki 2-Strokes: gt750

Re: 1977 GT750 Charging rotor.

Post by ryder2shae »

Thanks a lot for the info.I think am gonna order new regulator and rectifier.I will keep posted.
Cheers :)
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tz375
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Re: 1977 GT750 Charging rotor.

Post by tz375 »

I fitted an Electrex World RR77 I think it was called from the UK. It looks like a modern unit with a finned heat sink and the right connectors to plug straight in.

http://www.electrexworld.co.uk/acatalog/RR77.html" onclick="window.open(this.href);return false;
CBWELLS
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Suzuki 2-Strokes: Honda-350, SUZUKI GT550 x2, GS850, 92 VMAX,

Re: 1977 GT750 Charging rotor.

Post by CBWELLS »

You stated your "not fully charged" battery measured 11.5 volts. That's not only "not fully charged", but very likely has a shorted cell. I have to wonder how old & abused it is..... or if it just had an un-naturally short life possibly finished off by your suspected bad voltage regulator. I always tend to question the easy stuff (like the battery!) before going for the hard & expensive things.

You asked if directly driving the rotor with battery voltage is OK. I'd day YES since that is what the voltage regulator delivers during its normal full on cycle. When it actually "regulates", it inserts a resistance to cut down on the rotor current, thereby reducing the rotors magnetic field, which reduces the alternator output voltage.

I think you've eliminated most everything else and are left with the most obvious. I'd bet you have a wounded battery that's been killed by a bad regulator. By the way, there's not much in the regulator. If you were to open it up, you'd probably be able to see an open lead, dirty contacts, or something causing the problem.

Here's a cheap suggestion; Disconnect the bikes battery (just to take it out of the picture). Use jumper cables from a car battery to the bike's frame (NEG) and to the bike's POS cable. Take care about polarity, AND be sure the POS lead doesn't contact the NEG clamps or the bike frame (Maybe a 2nd person could help with that!). Start the bike as you would normally & do all your voltage checks again. If it looks better, you've found the weak link. Buy a battery before you go & do the other parts of the circuit. It is the most likely failure item.

Good luck.
ryder2shae
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Suzuki 2-Strokes: gt750

Re: 1977 GT750 Charging rotor.

Post by ryder2shae »

Thanks for the suggestions.The battery is new,just drained out when i was doing my tests.I just recharged the battery and am gonna buy the the new regulator/rectifier.My regulator had seen better days.Found these electronic regulator/rectifier on ebay.Not bad for the price,I guess.

http://www.ebay.ca/itm/310825164879?ssP ... 1438.l2649" onclick="window.open(this.href);return false;

Going to order one today and I will keep you guys posted as soon as I get it and Am gonna try the car battery like you said..
Thanks a lot guys.Much appreciated.
ryder2shae
On the street
Posts: 11
Joined: Sat Aug 16, 2014 1:30 pm
Country: Canada
Suzuki 2-Strokes: gt750

Re: 1977 GT750 Charging rotor.

Post by ryder2shae »

So,I fully charged the battery,cleaned all the connectors,directly connected the rotor to the battery.started the bike and tested the ac voltage at the stator wires and am getting 27 volts ac at 2500 rpm and 17 volts at 1500 rpm.Is this a good news or its not enough voltage ?

And I found a cheaper regulator/rectifier from china.Not sure how good they are but looks exactly like the Procom ones.Probably the same ones but way way cheap.Thought of sharing the link here guys.Worth a check..

http://www.ebay.ca/itm/160458381840?ssP ... 1439.l2649" onclick="window.open(this.href);return false;

Cheers
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jabcb
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Suzuki 2-Strokes: 69 T350 thru 75 GT750
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Re: 1977 GT750 Charging rotor.

Post by jabcb »

Those voltages are in spec. :up:
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 & 75
GT380 72
T500 69 project & 73 project
T350 69 & 71
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE
ryder2shae
On the street
Posts: 11
Joined: Sat Aug 16, 2014 1:30 pm
Country: Canada
Suzuki 2-Strokes: gt750

Re: 1977 GT750 Charging rotor.

Post by ryder2shae »

Sweet !!!! Thans :clap:
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