generator woes

My charging light came on and I put a voltage meter on the generator to find... nothing. Generator removed, brushes still there (just) but one of the leads had broken. Since I was already inside I replaced the bearing, inspected the bushing, replaced the brushes, repainted and reinstalled. Charging light is still on.

I checked the voltage from the generator and its only 1.2 volts at idle. Any ideas why it should be so low? Belt is tight, pulley is retained by the Woodruff key, contacts are all clean. Car is a 65 B.

i am no expert but i think you have to do something like polarize it or something.

Dwight
1979 MGB
Anchorage, Alska

I disconnected the lead from the regulator F terminal and touched it to the regulator B terminal. This should have polarized the system, according to my Chiltons' manual.

Does this polarization affect the regulator or the generator? And what, exactly, does it do?

I could be mistaken, but don't you connect the A terminal on the control box to the F terminal on the generator on MK I MGB? And by connect I mean swipe it across to make a small spark, do NOT hold it on there!

I double-checked in my Moss catalogue. For the record, this is a RB106 regulator used from 1962 - 1967, and the C40/1 generator, used the same years. Moss describes the process differently. They say to use a 14ga wire from the hot terminal on the fuse block and flash the field terminal of the generator. But that should be the same as the process in Chilton's. I disconnected the field wire from the regulator (which is connected to the generator) and touched it to the B terminal on the regulator (B for battery).

So what would cause my generator to give so little output?

You polarized it correctly, that's what's giving you the 1.2 volts and either the regulator is bad or you have a bad connection somewhere. Since you were able to polarize at the connections where you flashed the fields I'd say the regulator is shot. Flashing the fields where you did has nothing to do with the regulator failing if indeed that turns out to be the problem.

A quick and easy check to pin down the problem is to have the car idling and run a jumper from the B post on the regulator to the F post there or on the generator. If the generator is working you'll hear it when you make the connection. If it doesn't charge the problem is there, if it does the regulator is at fault.

DO NOT rev the engine past idle when running the above check and run the test only long enough to hear a diffeerence or not.

unless you are in a professional concourse career, put an altenator in that thing and it will be the last time you will have to do anything to a "Generator" :) :) :) :)
Hello that is the 21st century calling.

John, what should I hear? A spark? Clicking? I'll have to wait until tomorrow to try this as it has been pouring outside and my B doesn't like to get wet.

Jerry, An alternator would be a good idea. What other changes will I have to make? Obviously, positive to negative ground, tach, what else? I looked in the library but the conversions seemed to describe putting Saturn alternators into Bs which were originally equiped with alternators. What would one use for the regulator?

Thanks everyone for the advice.

I checked the resistance in the generator and it doesn't seem right. Field terminal to armature terminal was 7 ohms. Field terminal to motor block was 0.7 ohms and armature terminal to block was 6.3 ohms.

Shorting coils to the case? Might explain extremely low output.

Do the alternator conversion and you wont every have to change out another generator ever again. Of course then you will be changing Alternators :)

Oh to hell with all that ohm stuff, it will either work or it won't. When you run the test I told you about you;ll hear either the engine drag down a little or you'll hear the generator cutting flux. I can't explain what that sounds like but it's a distinctive sound. Kind of an electric whirring.

Two rebuilds and two replacements over 90K miles, my thoughts exactly, Carl...

I don't see how changing to an alternator will fix his regulator.

Oh, and I'm on my third generator... in 300,000+ miles! Can't say I've ever seen the need to replace it with a modern component. Maybe if I had a 3 million-watt stereo or something.... ;)

On installing a negative ground alternator.
I went 0 for two on converting tach's on my 67. Lots of scrap. My DPO could not do it either. He put in a Toyota tack I think. I sold the car.

The positive ground fuel pumps do not like this and wiil die in 12 months or less as I understand it.

Your AM radio will be history.

The generator is satisfactory and they cost:
$79.95 at VB new
$69.95 reman at VB
$110 at Moss
voltage regulators are $30

I do not plan on installing one anytime soon. Mine looks to be origional. Summer of 63.

Larry

Eric,

You didn't mention resurfacing the commutator. If you don't lots of times the rest of the work will be for naught. I have an ancient "organ grinder" commutator lathe but you can achieve nearly the same thing by either sanding the copper segments or chucking the armature into a big drill held in a vise and stroking the commutator lightly with a flat file. Remember to under cut the insulators just a little too. All this is explained in detail in the old shop manuals as it was just an accepted maintenance effort.

Get a specialty shop to put the armature on their test bench and test for a sort in the windings. It is a simple 60 second test.

Another fault could be an open circuit or direct short in one of the field coils. They are a bitch to replace so I suggest visiting a specialty shop for that one.

While you are at it, look for any evidence of a dragging armature. This will show as shiny places on the insides surfaced of the field coils and similar marks on the outer surfaces of the armature. If you see any, replace both support bushings.

jack

Like I said: It will either work or it won't with the simple test I outlined. If it won't work take it to a rebuilder and let them fix it. If it does work replace the regulator.

I too see nothing wrong with running a generator.

Yep, generators are just fine if the output requirements are not to great and the engine revs are not too high. Keep it. You can fix it from time to time if you have to. Jack

Problem solved! Thanks for your input. I thought that someone had suggested disconnecting the leads from the generator, putting a jumper directly from the armature terminal to the field terminal, and then measuring the voltage from the commoned terminals to the block. Can't find that now (John, did you edit that out?) Tried it and found 19V at 1000 rpm. Generator obviously was working. Did the test very quickly to avoid burning out the fine wires that make up the armature coils.

I opened up the regulator. Nice and clean, no corrosion. I probably changed it sometime in the last twenty years or so. But the resistance across the two normally-closed contacts was about 67 ohms. Should be dead short. Placed some 600 grit emery cloth in the contacts and pulled it gently through. Cleaned with circuit cleaner. Retested, less than an ohm. Put it back in and the charging circuit works perfectly.

I've been happy with the generator for the 24 years that I've had the car, so I guess I don't need to rush into an alternator.

Thanks again!

THAT is why I like non-electronic cars! Jack

Eric - Now tha the tgenerator is working correctly, loosen the fan belt. Running the fan belt tight with a generatoe is a way to destroy them in a hurry. The excess tension causes the armature to press hard against the rear bushing in the generator which in turn causes premature wear on the bushing. Pretty soon, the wear will be enough for the armature to make contact with the field coil shoes. See my article on fan belt tension at: http://www.omgtr.ca/technical/tdtf_fan_belt/loosen_up.htm
Cheers,

If you can't spin the fan with one finger, the belt is too tight!

Dave and Steve,

Thanks for the tip. I had the belt quite tight. Now when I press on it I get 1/2" deflection, just like it says in the Chilton's manual. I just assumed that tighter would be better.

Eric

Don't go by deflection, go by tension. Solid belts have les deflection than cogged ones so it depends on what type of belt you are using. When I can turn the fan with one finger but can't turn the generator pulley at all, I figure that's the right tension. Basically you want it as loose as possible without the fan or generator slipping.