MGB MGB1964 what i have?Dynamo,alternator,generator.

[zeque]

I bought a 1964 MGB (engine 18GB)a month ago, when i bought the battery was negative earth, the tachometer doesn´t work, i did it the conversion and now works fine. Now i am thinking in buying some essentials spares, one of them is the fuel pump, my problem start when the installed one is AZX1318 (positive earth) why? i dont understand.

My second question is about what have i in my car?, Dynamo, alternator or generator. (LUCAS 22700N 12v C40 28 69) i dont know what it is.

Thank you for your help

 

[PeterC]

Well, a 22700 is a generator also known as a dynamo.

I don't understand the first part of your question, though.

Peter C.

 

[tony barnhill]

What sort of problem are you experiencing?

 

[zeque]

Ok i understand i have a generator.
the other question is, why is my fuel pump(positive earth working perfectly in a negative earth car?,

Thank you for your answers.

 

[tony barnhill]

Your car was originally a positive earth car so everything in it was that way.....fuel pump doesn't really know which is which (thought somebody may come along to prove me wrong!).

 

[Dave Russell]

Re: MGB1964 what i have?Dynamo,alternator,generato

The AZX series of pumps use a diode for contact arc suppression. The diode is polarity sensitive & will "burn out" if it is connected with reverse polarity. Since the AZX1318 was built for positive ground, if it is connected negative ground, the diode will blow.

The diode failure would be pretty much undetectable & not much will happen except the contact arc suppression will not work & you will have burned pump contacts much sooner than normal. The diode can be replaced to restore the arc suppression.

The diode is a little round black plastic case with a red wire & a black wire sticking out of it. Moss has replacement diodes #377-135 for positive ground & #377-145 for negative ground. By installing the negative ground diode you have converted the pump from AZX1318 positive ground to AZX1307 negative ground.

If you are skilled at working on small electrical stuff, a garden variety one amp, 200 PIV diode could be soldered to the old diode leads instead of buying the Moss diode.
D
Note: older pumps used a capacitor instead of a diode & the capacitor is not polarity sensitive.

 

[tony barnhill]

Re: MGB1964 what i have?Dynamo,alternator,generato

See......hehehehe (glad I was at least 'right on' with the older pumps)

 

[David_DuBois]

Re: MGB1964 what i have?Dynamo,alternator,generato

Ok, everybody is partially right but not entirely so. The black cylinder that Dave talks about is a diode/resistor assembly, not a plain diode. Dave is correct is saying that the unit is probably burned out, which leaves the pump to operate just fine - until the points burn out because the arc suppression circuit is partially gone (the other part of the circuit is a swamping resistor that is buried, unseen inside the coil housing). Replacing the diode/resistor assembly with a plain diode will complete the arc suppression circuit, but will cause the pump to run slower than normal. I have a bunch of the Diode/resistor assemblies that I remove from pumps that I restore and convert to solid state and I can send one to you if you will e-mail me right away as we are leaving for California on Thursday for a week or so. My e-mail address is on my web site at: https://homepages.donobi.net/sufuelpumps/
Cheers,

 

[zeque]

Re: MGB1964 what i have?Dynamo,alternator,generato

thank you Dave, toni and david, all my doubt have been solved.
Thank you very much.