Positive earth fuel pump?

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jagnut66
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Positive earth fuel pump?

Post by jagnut66 »

Hi,
Below is my old fuel pump, which pumped merrily away on my journey back from East Croydon with my then newly acquired series 2 'Sally'.
Once home I put her up on axle stands and happily started a process of renovation, restoration and alteration.
One of said alterations was the conversion to negative earth.
This pump now refuses to function, necessitating its replacement (now installed).
From the outside the only noticeable difference is that it has a 'stepped' lid, the top of which is marginally narrower, this is more easily seen on the spare lid beside it.
Could this be a positive earth pump that won't work with a negative earth system?
Many thanks,
Mike.
DSCF3604(1).JPG
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1954 Series 2: 4 door: "Sally" -- Back on the ground with (slave) wheels and waiting to be resprayed......
1970 Triumph Herald 1200: "Hetty" -- Driven back from Llangollen in Wales (twice.....)
ManyMinors
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Re: Positive earth fuel pump?

Post by ManyMinors »

Mike, If your pump has contacts in it, then it won't be polarity sensitive and will work either positive OR negative earth.
It is only the electronic pumps which are polarity sensitive.
It isn't unusual for pumps to "give up" after a period of inactivity. It can probably be brought back to life again with a bit of work or new contact set etc.
StillGotMy1stCar
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Re: Positive earth fuel pump?

Post by StillGotMy1stCar »

It’s what is under the lid that is important.
As above
If it has a circuit board or has a transistor retro fitted then it is positive earth only, but can be made negative earth by replacing the circuit board with a negative earth type or the better still go back to points.
If it has points then it will work on positive or negative earth, the only thing you need to check is what is fitted across the points to suppress the arcing, for a while they fitted a zener diode which will have a black lead and a red which will need swapping around. Earlier than that they fitted a capacitor and later they fitted a Transient Voltage Suppression Diode or a varistor, so many options, you may even find a diode across the coil.
Capacitor or varistor will work with either polarity, if a TVS diode is fitted it depends on the type, they come in bi and uni-directional, to be on the safe side reverse the diode if fitted.
May just need the points cleaning if you haven't already.
It would be nice to have a photo of what is under the cap.
Regards John
jagnut66
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Re: Positive earth fuel pump?

Post by jagnut66 »

for a while they fitted a zener diode which will have a black lead and a red which will need swapping around
That may be something I need to address then, time to get the soldering iron out......
Pictures for you below, I have already swapped out a few items with better ones from my spares stash (I have all sorts of things in those piles, it'll give my executors a real headache, when the time comes! :lol: ) in an effort to get it working but I didn't swap the red / black wires over......
I'll need to reposition some of those wires too, as it looks like the cap is rubbing them.
If I run a live and earth direct from a battery and connect them (briefly), I take it that it will tick like mad, if it works?
Many thanks,
Mike.
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1954 Series 2: 4 door: "Sally" -- Back on the ground with (slave) wheels and waiting to be resprayed......
1970 Triumph Herald 1200: "Hetty" -- Driven back from Llangollen in Wales (twice.....)
StillGotMy1stCar
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Re: Positive earth fuel pump?

Post by StillGotMy1stCar »

No you're OK, put the soldering iron down, it has a Varistor fitted, should work positive and negative earth.
The Black/Red wires go to the coil, that should work either way unless something else has been hidden inside with the coil.
Regards John
IslipMinor
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Re: Positive earth fuel pump?

Post by IslipMinor »

When we fitted an alternator back in the 70's, and converted the Minor to negative earth, it had the original fuel pump which worked fine after the conversion, with no mods to the pump at all. As has previously been stated, it is only the 'electronic' versions that are polarity sensitive.
Richard


jagnut66
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Re: Positive earth fuel pump?

Post by jagnut66 »

Well I put it all back together, attached an earth wire and a feed wire to it and the battery on my car (car electrics disconnected), nothing.........
Could it be the coil inside it has packed up, not unreasonable considering its age. I have another spare pump of the same type, though it seems to be possibly an earlier design (off God knows what) which is equally dead.
Best wishes,
Mike.
1954 Series 2: 4 door: "Sally" -- Back on the ground with (slave) wheels and waiting to be resprayed......
1970 Triumph Herald 1200: "Hetty" -- Driven back from Llangollen in Wales (twice.....)
StillGotMy1stCar
Minor Fan
Posts: 433
Joined: Wed Jun 07, 2017 11:37 pm
Location: Carmarthenshire
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Re: Positive earth fuel pump?

Post by StillGotMy1stCar »

If you have a multimeter check the coil resistance, from memory expect a low ohms reading of between 3Ω to 6Ω, whilst your at it measure across terminals that the blue varistor are connected to, that should be zero ohms (the same reading as joining two meter probes together) as it is the points connection as well and needs to be closed to work.
If you haven’t got a multimeter another way to check the coil is to put 12V across it and see if it pulls the diaphragm, you should see the points rocker throw over.
Chances are you haven’t got a current limited power supply so be careful when using leads direct from a car battery as they will quickly heat up if shorted.
If you get no movement but get a spark as you touch your leads to the coil then the armature is jammed.
If you get movement then the points need checking
No spark and no movement would suggest the coil is open circuit.
If the coil is open circuit it is worth investigating further as it might be a poor or broken connection that is repairable. See Sandun’s video about removing the coil.viewtopic.php?f=4&t=72026


I know it is only a spare so you’re probably not bothered if you get it working but one other thing I noticed is that the varistor fitted is the wrong value, it’s 85V so isn’t doing it’s job of extending your points life, it should be a 14V or 18V version. A better replacement is a TVS diode (also known as a Transil and Transorb) type 1.5KE24CA it is not polarity sensitve.https://ttypes.org/extend-the-life-of-y ... a-transil/

Regards John
jagnut66
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Location: Mansfield, Nottinghamshire.
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Re: Positive earth fuel pump?

Post by jagnut66 »

No spark and no movement would suggest the coil is open circuit.
Reading through your post this is the statement that best describes where I am with both of my spare pumps. So time to delve into the realms of the coil at some point then.
I noticed is that the varistor fitted is the wrong value
Interesting, as this would have come off a pump I would have stripped for spares, so was originally in use with one of these.....
Shame I didn't think to extract the coils, I might have had a good spare! Doh! :lol:
Best wishes,
Mike.
1954 Series 2: 4 door: "Sally" -- Back on the ground with (slave) wheels and waiting to be resprayed......
1970 Triumph Herald 1200: "Hetty" -- Driven back from Llangollen in Wales (twice.....)
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