Alternator Charging Question

[Arundel2]

It is winter here in New Zealand so i have not been out riding much at all. My 1979 cbx is always connected to a battery tender so i have not tryed to resolve its charging issues.
I finally decided to have look again at whats going on.Started up bike and put multi-meter on battery and got about 12.5v-13volts at 1500rpm.At 3500rpm- 4000rpm i had 13.5v-14volts at the battery,but as motor warmed up more this reading dropped to 11.99volts.I had no charge coming into battery at all.
I do need to bite the bullet and fix before summer comes but do not want to replace parts willy nilly in the possible hope of fixing problem.
Would it be that because its charging when cold and not when hot that the clutch is at fault?
Have checked and cleaned red connector where power comes from alternator.
Bike is original ex Florida bike with only 13000 miles on clock.
I am not good with a multi-meter but am willing to learn.
Any advice as a starting point would be gladly received.

Mike Seelen

[daves79x]

There are some checks to try with the alternator in place, but you need to take the alternator apart to see what's going on in there. Separate the alternator and see what the brushes look like. If the outer one is near the scribe wear line, then that's likely your problem. 12,000 miles was about the limit for early model alternator brushes. If the brushes are good, next check the resistance between the 2 copper slip rings. It should be 4 OHM, plus or minus a couple of tenths. If near zero or way higher, then the rotor is bad and needs rewound. This is the most common CBX alternator failure, next to brushes. If this test is good, then check the stator. All 3 yellow wires should have continuity with each other but not to ground. If that test is good, then it's likely your regulator/rectifier. I should also add that you must have a good, properly charged battery. You can do a static load test by just turning on the lights with the engine off and watch the voltage drop - should only be half a volt or so and the lights should stay on pretty bright.

Check the condition of the bearings and seal. If there's evidence of oil in the dry side of the alternator, then I'd replace both bearings and the seal, plus the shaft o-ring. Then measure the clutch spring. It should measure near 30mm. Much less and it's gotten hot and sacked out. Make sure you have the thick fiber washer shim on the drive plate, as well as at least one steel shim washer. Another won't hurt. Also the clutch plate condition. They'll look pretty grooved, but should not be discolored. The 4 oil slinger grooves should still be present on the drive plate.

That'll keep you busy for a while. You'll need a new gasket as well.

Dave

[steve murdoch icoa #5322]

Mike, here is some additional info to check through, courtesy of Mike Nixon.
http://www.motorcycleproject.com/motorc ... charge.swf

[Larry Zimmer]

Mike, I'll add one more thing to Dave's good stuff. Check all the connectors between the alternator and the battery. I'm not as familiar with the '79 as with the '81/'82. However, any of these connectors carrying the primary charging current are subject to corrosion over time. It doesn't take much resistance increase anywhere to present a measurable voltage loss. (Example: 0.5 extra ohm resistance through a connector at a 5 amps charging load [70 watts] represents a voltage drop of 2.5 volts.) You might do this checking first before 'diving' into parts. A thought.

[EMS]

You might do this checking first before 'diving' into parts. A thought.

I was going to hint the same thing. Especially as resistance increases with temperature. But he said he cleaned the connectors...

[Larry Zimmer]

DOH! Missed that part of his note. Onward to the hard parts, then.

[daves79x]

My idea is - if you bought a CBX with an unknown alternator service history, that'd be the first thing I'd be checking - it at the very least needs the brushes looked at and cleaned out inside.

Dave

[Jeff Bennetts]

DOH! Missed that part of his note. Onward to the hard parts, then.

Larry you still have a valid point, a lot of people don't realize that corrosion can build up where the wire crimps to the rear of the spades in the connector, it's easy to miss if you're not looking at the back of the connector. If any wire is shinny, brittle or discolored where it enters the rear of the connector, it's a good idea to release the spades from the connector with a dental pick and look them over.

[Larry Zimmer]

My idea is - if you bought a CBX with an unknown alternator service history, that'd be the first thing I'd be checking - it at the very least needs the brushes looked at and cleaned out inside.

Dave

And, how!!! Brush powder makes one hellacious mess!

[Jim-Jim]

All good thoughts here and all valid especially the connector where the alternator plugs in.
A quick check is to look at the plastic housing of the two joining connectors. If there has been any resistance of any note, there will be BROWN BURN marks on the plastic shell, particularly where the 3 Yellow wires come in. But even if there are not burn marks, it's a good idea to remove all the wire (make careful note of which go where) and clean the contacts. If you're handy with a soldering iron, it will help if you solder the 'crimp' which can corrode inside the small wire bundle.
But the charging voltage is good at start so all of those parts are OK. When it decreases with heat (but doesn't drop to 0), then I think resistance is building up and I would look at the connectors. I can't see short brushes doing this and I've not seen either the Rotor or Stator decrease; usually they just quit (open). I would think a 'heat' related problem in them would just 'open' up and the meter would drop to battery voltage.
Arundel, you said the meter showed 11.99 - was this battery voltage or a lower voltage from the R/R? If you kept running, did the voltage continue to drop (battery discharging) or did it hold steady at 11.99? If it continued to drop, then, indeed, you lost all Alt voltage coming in. Then the aforementioned checks (Rotor and Stator) should be checked. If they check OK, you need to warm them up to see if there is a 'hot' open on one of them. It might take some doing but, maybe, you could disassemble the alt, place the Rotor in the oven to about 200-250 or so and quickly check the resistance on the rings. As said, it should be right around 4.0 ohms. The Stator is a little different. Heat it up and then look for continuity between each of the three yellow wire legs; if one winding opened up, one check will show '0' ohms. Usually, the R/Rs don't have heat problems but............
Do these one at a time and let us know - as you can see, lots of help here.
J-J