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MG MGA - need help again

hi all,
Thanks for the comments about the air filters.The most important thing I learned is no cheap pan cake filters on the A.
BUT.After the air filter cleaning I started the car and the ingnition light stayed on.So I disconnected the generator,shorted the D and F poles, put a V meter between D en earth, started the car and... nothing.No output voltage(1000RPM).Removed the generator.On the work bench I checked the brushes, ok.Measered the resistance of the field coil and was 6,3 ohm.Shortened the D and F again and putted 12V between D and generator body.The generator started spinning.So he looked good to me. I have a spare, not overhauled generator.I tested it on the bench and he looked ok.I putted it in the car.Shortened D and F,meter between D and earth, started the car and nothing!!If he was ok he should give 12v I think.
So or I have two generators who tested ok but do not give any voltage when I test them in the car.
Or I do something wrong.
Any help and advice is more than welcome.
Herman
H. Jorens

Herman, next you should check the voltage regulator. A new one is only about $45 from Moss.
ArtPearse

Yes Art, but even without the regulator.When you disconnect the wires from the generator and short the terminals D and F and then start the engine there should be 12 to 14V between D-F and earth.If not the generator is defective.But the strange thing is when I remove the generaor from the car and put 12V between the shortened D and F poles and earth, the generator starts spinning like an electric motor which suggests that the generator is ok.
H. Jorens

You mighgt have reversed the polarisation of the field.
Put 12 V on the field from the car's battery for a second or so to get it's polarisation right.
Also test the D+ voltage without field current which should give some 5-6 V with engine revving up indicating that the armature is OK.
Dirk/Antwerp
D. Van Ussel

Herman - did you rev the engine up when doing the test with field and output terminal together? Just watch the meter closely when you rev the engine so that if the voltage shoots up quickly, you can drop the revs down. If you still don't get any voltage start looking at the brushes, brush holders and other terminals on the end plate for shorts using the ohms scale on your meter. Cheers - Dave
D W DuBois

This thread was discussed on 12/02/2015

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