Topic: Shorted Stator? Did I do that...

[dperl]

So I have an electrical question!
I have my suspicions but wanted to reach out in advanced of testing anything out to see if I could find any leads before diving in.

Bike ran absolutely fine up until I dug into the left cover to fix my starter clutch. Here's what has happened - the coil inside my stator came loose and touched the coil itself. I heard what I now believe to be a sparking noise, but didn't think much at the time.

Anyways, cleaned everything back up together. When I went to start the bike for the first time since, a few of the pilot lights were out. Figured I may have sparked something that caused that. Anyways, its been a few days since and my bike completely died on me last night. Total loss of power and died on me while running. I hadn't had it on a charger or anything since, but the battery was completely drained.

I haven't had a chance to test anything yet, but I've got my bike on a charge now. So, couple things. 1) Would the field coil touching the stator cause a short and mess up charging? 2) Where you recommend I start with testing and eliminating variables?

Thanks!

[flybox1]

pop a fuse?

[Bodi]

Nothing in there is powered with the key off, unless you already had a bad rectifier. With key on you would almost certainly blow an electronic regulator by shorting the field coil power wire to ground  - the mechanical one would probably survive ... it would probably blow the MAIN fuse as well. You can do anything you care to with the three stator wires, if the bike isn't running (key on or off). These go only to the rectifier input, to diodes that will block current if you ground any wire or connect it to battery +.

[dperl]

Anyways, cleaned everything back up together. When I went to start the bike for the first time since, a few of the pilot lights were out.

More than likely, you pulled loose the BLUE/RED wire and the GREEN/RED wire which feed the OIL and NEUTRAL light respectively. Both connect/route under the left side cover of your bike, and connect through the 8-way plug with the stator wires.

Would that lead to the bike completely draining and not holding a charge? I test the voltage at the battery at idle, and then revving - no increase at all, stays around 12.3v. Would that be the case if the worse came loose?

[scottly]

First of all, what bike? Second, there is no way the stator could hit the field coil, since the field goes on the inside of the rotor, and the stator goes around the outside of the rotor. If the field was loose and contacted the rotor, disconnect the white and green field coil wires from the harness and measure for continuity to the engine case: there should be none. If that tests OK, measure the resistance across the white and green wires; it should be about 5 ohms for a 550, and 7 for a 750. If the stator hit the rotor, disconnect the three yellow wires from the harness and measure for continuity to the engine case: there should be none. You can try to measure the resistance between the three yellows, but be aware that the normal values of .2 ohms are beyond the capabilities of most meters, so for now just look to see if all combinations are the same.

[Bodi]

What you describe is the effect of the alternator not working - that battery discharges until the bike stops because no spark, and all lights are very dim.
So look into what has happened... the alternator wires have bullet connectors under the side cover, most likely one or more were pulled out when you took the alternator off if you left it hanging by the wires while you worked on the rotor. While you're there, clean and snug up all 5 of the alternator wire connections as they are prone to corrosion under there.
Maybe the field coil power wire (one of the whites) shorted to ground and burned out the regulator, do you have a (sensitive to such indignities) electronic regulator?
Nothing you can do with the yellow wires (within reason... plugging them in the wall would be a disaster) would damage the rectifier but it should be checked anyway, there are plenty of diagnostic procedures online using a multimeter or test lamp to check all six diodes in it.
Mechanical damage can destroy the field or stator coils but it would probably be obvious, and the Ohms test above will tell the tale.

[dperl]

Apologies, we're working with a '77 CB750 here.

A few questions, and please forgive my lack of specific knowledge and technical terms. Learning as I go here..

1) I opened up my case again to find that one of the wires from the field coil was breaking at the connection. The plug came off pretty easily, I'll have to throw a new connector on there. If the stator was still hooked up properly, could the unconnected yellow wire be the cause of the bike not charing?



2) It's super tricky to get to the connection points from the stator that then lead under the left side cover. It's not a single connection, theres some plugs that connect behind the starter motor - its such a tight fit, not at all easy to get to, let alone see. The connecting wires appear to still be in tact. If they were all still connected would I be getting continuity at this connection?



If I should be getting continuity, how would I check? There are 4 yellow wires that run into this plug. Set to ohms on the multimeter and go between connections?

[bryanj]

Should be 3 yellow wires that go to the outer coil then a green and a white that go to the inner coil, resistances are specified in the manual but are low so difficult to check with the normal multimeter.

Basically as long as the resistance is the same between each of the 3 pairs of yellows and low from white to green with an infinitely large resistance to ground it should work.

In 40 years I have not seen one of these go duff electrically, only mechanically after accident

[Bodi]

The wire colors have faded from heat and dirt over the decades. The shell connector is probably OK, the spade connectors are more robust that the bullets. A problem usually causes the connection to heat up, overheating turns the white plastic shell brown or black around that connection and I don't see this.
Yes the wires a difficult to work on. The entire engine harness from the white plug to the bullets can be pulled out but it isn't easy to get back under the various clips. I think the neutral switch wire is in the shell as well.
Probably the three wires close together are to the stator coil. In theory they used to be yellow. Then the other two hanging would be to the field coil, I recall them as originally being white.
Neither set cares about order or polarity. The field coil wires should have male bullets and the stator coil female.

If that field coil wire was broken during your ride you would have zero alternator output, causing exactly the result you experienced.

[strynboen]

or only 8 volt..from the 2 fases left working
..but not any power to hold the battery going..all 3 yellow vires must konnekt right over to the other 3 yellow vires through the konnektor

[scottly]

Field coil with white and green wires and male bullets is on the top.
Stator with what were originally three yellow wires and female bullets is underneath. The part these pieces are bolted to is referred to as the alternator cover.
If you remove the sprocket cover, behind the shifter cover, it may be a bit easier to access the bullet connectors.
 

[bryanj]

Just looked in old manual and the resistance green to white should be 7.2 ohms and between each pair of yellow wires 0.2 ohms. These numbers are too low to get an accurate reading with the "generic" multitesters out there

[PeWe]

Problem is on the alternator side?
The other side harness is available new. When Yamiya has it, it will most likely be found closer too.
http://www.yamiya750.com/index.php?main_page=product_info&cPath=246_21_250_58&products_id=1945