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MG MG Y Type - Charging problem

My YB is not charging. The ammeter reads a bit negative, and the volt meter confirms this. Battery voltage with the car off is 12.5 volts and running it is 12.3 volts.

I tried to check the dynamo but the spark wires must not be insulated because the meter goes crazy whenever I get near it. Or could it be something else? Is there a way to check this thing without removing and disassembling the generator?
Steve Simmons

Steve

The iginition HT wires must be insulated or you would be getting very high voltage shocks and big misfires.

You say the battery is 12.3v - that is OK. The ammeter will normally read slightly under on idle. This is normal - do not worry.

Provided the bushes are in good condition in the dynamo there is very little to go wrong. The fan belt must also be the correct tension too.

Paul
Paul Barrow

I adjusted the fan belt but it made no difference. The ammeter reads low at all speeds. The fact that the battery reads lower with the car running than not running suggests that it is in fact draining. I drove the car last night using all the lights. THe ammeter read very low, probably -20. When I connected a battery charger to it, the battery was paritally drained.

What is the best workshop manual for this car? Sounds like I need a wiring diagram. I should at least test the voltage regulator I suppose, once I figure out which leads to test.
Steve Simmons

Steve

The best Workshop Manual for the MG YB is the original workshop manual. These are available as reprints (recommended for working on the car, as oppossed to sitting on the shelf in the lounge room). Reprints are available from the MG Octagon Car Club - see Links page for link and remember to ask for one for the YB and not the YA/YT.

Wiring diagrams will be posted shortly on the Technical Data page, however these will not cover mods made to your car but be factory standard ones.

You may have a short to earth somewhere, or you may also just have worn bushes in the dynamo, or the voltage regulator may be cutting out. If you adjust the latter, be very careful - I have recently heard a lot of stories about people incinerating their cars, and nearly themselves by adjusting these and not knowing what they were doing!

Good luck,

Paul
Paul Barrow

Take the battery lead of with the car on a fast idle if it stops it's not charging. If it keeps running it is! it should run with the lights on to if it's charging enough.
John Arkley

Steve

It sounds to me like your generator is not charging the battery. My initial guess it check the voltage regulator. It could be as simple as dirty points. These regulators are rugged. My original factory regulator lasted until sometime in the 1980s.

There is a good procedure for checking the charging circuit in the factory manuals. I happen to like the one in the TD manual that I have. It is old and smudged but if you would like a scanned copy contact me by email and I can try and scan it in tonight.

Suggest that you start "collecting" the various manuals and parts lists.

Larry

49 YT (since 1961)
Larry Hallanger

I have (or had I hope) a charging problem on a recently bought Y too. As suggested above I removed the battery lead and the engine stopped.
I removed the dynamo and cleaned and degreased the bushes and collector (and fitted a new ball bearing); very satisfying work that is.

An "old hand" here at work told me you can test a dynamo by connecting it directly to the battery; the dynamo then acts as an electric motor and should turn at a low speed (+/- 120rpm?). I did this and it turned, so I sure it will work again!

I also read somewhere that it is important to "prime" the dynamo (to polarise it?) by letting it work as an motor for a few minutes, but I also read you can ruin the regulator if you polarise it the wrong way.
So now I am in doubt how to connect the poles: I think the minus-pole of the battery should be connected to the big isolated connector on the dynamo (the car has positive earth) and then of course the plus-pole to the smaller connector. I have a later type dynamo on which you have to remove the back to access the brushes.
Willem van der Veer

I too had the same problem initially on my YA.... three things came to light after many peoples opinions had been passed, very few of which were qualified (which always causes me some confusion).

Firstly the voltage regulator was cleaned and tested and was not functioning correctly. After sourcing another two second hand units, we finally came up with one that produced the goods (though the qualified electrical engineer concerned did tweek the outputs). Secondly the fan belt, though tight, WAS slipping at higher speeds. Finally the original battery that came with Agatha (not a true original!) was tested by a professional and was proven to be past its sell by date (wasn't holding charge). A new & much uprated battery, that still fits in the offset box, has now been fitted.

When all was done she now starts on the button every time (touch walnut!!!).

Kindest regards

Ken

PS Agatha is now negative earth after the restorer 'polarised' the dynamo and changed necessary wire connections.
Ken Jones

To polarise the dynamo Use a small piece of wire and momentarily (about one second) touch it between the regulator terminals marked "Al" and "F" or the way I do it get a long piece of wire from the 'LIVE' side of the Battery and touch the other end on the small terminal on the dynamo. It will make a few sparks so don't think you've hurt something.
John Arkley

Ken, shouldn't that be positive earth, or have you had your car repolarised and switched?

Paul
Paul Barrow

In reply to Paul's question, I thought my original words were fairly clear ie "Agatha is now NEGATIVE earth after the restorer 'polarised' the dynamo and changed necessary wire connections".

This was achieved by the 'flashing' method exactly as described by John Arkley and has always been common practise in the mototr rewind trade.

Other than my dash meter now shows 'negative' volts for a positive charge (must change those terminals round too one day!) all seems wonderful.... whether there was any benefit for this conversion, you'd better ask a sparky (or Neil) but it certainly seems to have done no harm.

TTFN

Ken
Ken Jones

Negative earth car is a far as I no supposed to not rust as much as a positive earth one. But looking at cars of the 1970s it may to make them Rust!
p/s remember if you have a clock that works it won't with Negative Earth.
John Arkley

A working clock? wow! I think that in "M.G. Y Type & Magnette ZA/ZB by Brooklands" an old article was reprinted about an used Y (then a few years old) and even then they mention "as usual the clock isn't working....". My clock is about half an hour late (per hour, that is) but maybe it will run faster with the correct voltage due to the repaired dynamo! I will try tonight.
Willem van der Veer

Clock speed - if working, is determined by the state of the battery really more than the charging system.

A working clock will drain a battery if the car is not used frequently.

To restart a clock from "STOPPED" (as opposed to "not working" press in the adjuster and hold it in for a few seconds.

The main problem in the clocks is the points sticking and burning together. They can be repaired but it is not cheap.

An alternative to repairing your clock, and getting quartz accuracy, is to fit a replacement mechanism. There is a kit available from the Netherlands (I think it is Bert Keuren) but there is a thread somewhere in the BBS archive on it. I think Jack Murray fitted one of these and is delighted with it.

Paul
Paul Barrow

As Paul correctly states, I have fitted one of Bert's quartz movements and I am very happy with the result. I also know of a TC owner who went down the same route and is also very pleased with the fact that he has a 'working' clock. The modification is quite straight forward and is invisible to the untrained eye.

Jack
Jack Murray

Link to said parts? :)
Steve Simmons

Steve

I have sent you Bert's details off-Bulletin Board. If anybody else would like to contact Bert for one of his replacement Clock Mechanisms, I will let you have his details.

Regards.

David Pelham

This thread was discussed between 09/08/2003 and 31/08/2003

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