S1 1952 80" Generator tips

[NobbyTD5]

Hi all
So I have it running and it seems to start and run each time - which is nice

but I noticed that the amp meter is slightly negative and that the battery slowly discharges - using my multimeter on battery to measure voltage.
I reversed polarity to positive earth and it was no better and in fact ammeter seemed worse, voltage dropped quite quickly and the (newish electric replacement) fuel pump does not pump
So i guess it is configured Negative Earth.

Does anyone have any ways to test the Generator or things to check - connections, fuses etc - before I pull it off and potentially refurb it etc?

Thanks


cheers

Scott

[Old Farang]

All is revealed here:

https://www.mg-cars.org.uk/imgytr/pdf/lucascourse4.pdf

A quick check is to remove the fan belt and momentarily close the cutout relay in the voltage regulator. The generator should then run as a motor.

Doing that will also "flash" the field coils to the correct polarity whichever way the battery is connected.

[Old Farang]

(newish electric replacement) fuel pump does not pump

Some replacement electric fuel pumps will only run on a negative earth connection.
Are you sure that you have the correct low pressure pump? Any more pressure will lead to carby problems, should only be 2.5 psi.

[JDNSW]

In the voltage regulator, the cutout relay is the one wound with thick wire.

[Old Farang]

In the voltage regulator, the cutout relay is the one wound with thick wire.

Yes, I should have pointed that out!

Carefully remove the bakelite cover and facing the regulator it is the relay on the lefthand side.
You will be able to see the small, hinged metal plate that has a rounded edge at the top of the relay. The actual cutout contacts are underneath and difficult to see, and there is only a small amount of movement when you push it.

Disconnect the battery just to make sure what is what, then reconnect it to flash the generator.
It may want to stay closed, so it is good practice to leave one battery terminal loose so that you can pull it off.

I have the complete service book on how to set up the regulator, but right now it is on my computer, and I would have to find a way to extract the relevant pages.

[NobbyTD5]

Thanks OF - yes I am quite sure I don't have the right fuel pump! - it suspiciously looks like a cheap ebay one and it does over pressurise the fuel system (I originally thought it was a float issue in Carby but you are right, overpressure is the real culprit) . Looking at a Lucas one now - back to original!

Pump is also wired negative earth and using JDNSW's guidance the car is positive earth - the ammeter indicated positive earth with headlights

I am still surprised that the motor runs happily either way!

I think prior owner was playing around with the fuel pump etc but never finished off the job - they did do up the brakes and they work well - which was good thing!

I will keep playing!

cheers Nobby




[COLOR=#333333]

Some replacement electric fuel pumps will only run on a negative earth connection.
Are you sure that you have the correct low pressure pump? Any more pressure will lead to carby problems, should only be 2.5 psi.

[NobbyTD5]

OF and JD

Thank you - really appreciate the thinking and guidance

yes I think that sounds like my next step - flash the generator and then replace the fuel pump. (and get radiator weeps fixed!, replace radiator hoses...)

I will also need to check fuses - as headlghts seem to be not working now?

It seems a bit of a wackamole situation - but I will get there slowly but surely

I am very happy it runs nicely!

cheers

Nobby



Yes, I should have pointed that out!

Carefully remove the bakelite cover and facing the regulator it is the relay on the lefthand side.
You will be able to see the small, hinged metal plate that has a rounded edge at the top of the relay. The actual cutout contacts are underneath and difficult to see, and there is only a small amount of movement when you push it.

Disconnect the battery just to make sure what is what, then reconnect it to flash the generator.
It may want to stay closed, so it is good practice to leave one battery terminal loose so that you can pull it off.

I have the complete service book on how to set up the regulator, but right now it is on my computer, and I would have to find a way to extract the relevant pages.

[Old Farang]

I am still surprised that the motor runs happily either way!
The ignition coil does not really give a **** which way the DC current flows through it.
The condenser MAY object eventually, and the points are just switching the current flow through the coil, so are also not concerned. SOME modern coils, or some that use a ballast resistor, will not work, or fail, so just use the recommended coil. Setting the gap on the points is more important to good running, along with the spark plugs.

5380, a poster on here, is the carby man to go to if you are having any problems with it.

[JDNSW]

As far as the engine running either polarity - really, as pointed out, there is in practice no difference what polarity the engine is running on.

There is a theoretical advantage to running negative earth, as it will slightly reduce erosion of the centre electrode of the spark plugs, but in practice, there is no perceptible difference. There may have beenwhen spark plugs were expected to last through multiple cleaning sessions, but for many years it has been normal practice to simply replace them if at all suspect.

[LR1953]

If your generator output is low, check the brushes. And while you have the brushes out, check the commutator.
Cheers Rob

[LR1953]

Thanks OF - yes I am quite sure I don't have the right fuel pump! - it suspiciously looks like a cheap ebay one and it does over pressurise the fuel system (I originally thought it was a float issue in Carby but you are right, overpressure is the real culprit) . Looking at a Lucas one now - back to original!

Pump is also wired negative earth and using JDNSW's guidance the car is positive earth - the ammeter indicated positive earth with headlights

I am still surprised that the motor runs happily either way!

I think prior owner was playing around with the fuel pump etc but never finished off the job - they did do up the brakes and they work well - which was good thing!

I will keep playing!

cheers Nobby

I think the original pump was SU pos. earth. Now available in neg. earth. Not cheap but supremely reliable.
Cheers Rob S

[JDNSW]

I made a mistake (blame it on jetlag). The theoretical advantage is for positive earth!

[5380]

I think the original pump was SU pos. earth. Now available in neg. earth. Not cheap but supremely reliable.
Cheers Rob S

The low pressure (1.5 PSI) SU pumps used on Series Ones were all originally hooked up to the standard positive earth system. If they still have points, they don't care if it's positive or negative earth. The later electronically switched pumps are polarity sensitive. Also some SU pumps may have some form of electronic assistance fitted to minimise the current flowing through the points to cut down on spark erosion on the contacts and may be polarity sensitive. If you have an old (Pre 1985) SU LP Pump an SU EPK700 rebuild kit will make it like new again and give years of reliable service. Kits cost about $135.00 last time I bought some from Classic Carburettors. The Solex 32PBI-2 carb can't cope with much more than 2PSI reliably, so don't waste your money on ebay cheapies that are nostly in the 4.5 - 6 psi range.
5380