SU fuel Pump AUA66 (points) Overhaul Guide

[svenedin]

I just thought I would make a post about fuel pumps. There are loads of posts about fuel pump problems but no thread encouraging people to do routine maintenance on the pump. My pump was an absolute nuisance for years and I always blamed it on the points. I just had the pump to bits and it was nothing to do with the points at all. The insides of the pump were coated in nasty sticky fuel residue and it was a miracle the pump worked at all. Petrol and a toothbrush did not remove the residue but carburettor cleaner was very effective. The disk type brass valves were completely stuck.

I found a good article on pump restoration by Cliff Knight here: http://www.mg-tabc.org/library/fuel_pump/supump2.html

Make sure you have all the replacement parts you might need before you take the pump to pieces. At an absolute minimum this will be the gaskets, fibre washers and sealing washer but you will probably want to replace the diaphragm and the points at the same time. It is silly to try to reuse an old gasket or washer because a petrol leak could be very dangerous. New rocker assemblies and blades from SU have twin points rather than the single point on old pumps so they should be more reliable. If you wish you can buy a kit to convert to electronic rather than points. I rather like the reassuring tick tick of the points type pump though.

A couple of things are not mentioned in the article: old pumps (like mine) appear to use asbestos gaskets so take due care with these and dispose of properly. New gaskets are not asbestos. Also, if your pump has brass rollers be careful when you take the diaphragm off -they will all fall out so don't lose them. It is essential that the diaphragm is adjusted correctly (see article) and that the pump is connected to power and the points held closed prior to completely tightening down all the screws. This ensures that the diaphragm is at its maximum forward throw when the pump reassembly is complete.

It took me about an hour to do the whole job which included taking the pump off, stripping down, reassembling and reinstalling. The difference is dramatic, it works perfectly now. I should have done this job years and years ago. Anyway, don't blame the pump for being rubbish. It isn't rubbish, it's beautifully designed but yours is probably long overdue an overhaul!

One other point, these pumps do not like dirty old fuel. I completely overhauled my pump and it stopped working just a week later. I cursed the pump for being useless but it was horribly stuck again because my petrol tank had such disgusting fuel in it. I drained all the fuel out of the tank from the drain at the bottom, rinsed out with fresh petrol and refilled. All is well again. Not as good as taking the tank out completely and cleaning it but it has worked for now.

Lastly, old pumps have diaphragms that were never designed to cope with modern fuels. The culprit here is probably the ethanol that has been added to petrol. Current UK petrol (E5) has 5% ethanol but up to 10% (E10) is now allowed. This is an EU "eco" directive. It's madness because rainforest is being cut down to grow crops to make ethanol but that's off topic. What's on topic is this ethanol attacks the rubber used in old fuel systems and also damages the alloy used in carbs etc. A new diaphragm will cope with modern fuel so it's best to change it.

All the parts from a tiny washer to a brand new pump are available from SU and there is also an overhaul kit with all the parts you need for a major overhaul.

[Tudge]

Great find! Thanks very much, link is favourited.

[don58van]

Thanks so much for sharing!
Regards
Don

[Old_Robin]

Excellent posting. Thanks
Old-Robin

[svenedin]

An old thread of mine but I have just rebuilt another fuel pump and this time I made a short video of testing.

Here is a pump adjusted to run properly with the correct gaps set (see diagram). This is critical. If the gaps are wrong the pump will not run at all.

The spark suppressor (bi-directional, dual polarity, Burlen CZX 1004) is difficult to install correctly. Great care must be taken not to snap off the connectors or break the wires from the component. It does work very well and there is no obvious sparking in operation with it installed, greatly prolonging the life of the contact breakers. A cap with a bulge should be used.

The SU workshop manual is strongly recommended and a 2BA spanner is useful too.

A small 12v battery such as used in burglar alarms is very useful for testing car electrical equipment.

Incidentally (this is well known) if you run the pump with the cap off the points hinge pin tend to fall out. It's the cap that stops this happening.

Stephen

https://youtu.be/gjgqomqR7x4 (video of pump running with cover off)

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[svenedin]

The pump above had been run without a spark arrestor. The old points show severe pitting which was irretrievable. I have no idea how long it took for those points to get so burned.

The diaphragm had delaminated too

Stephen

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[myoldjalopy]

That is interesting about the spark suppressor. I have a normal capacitor fitted externally (to the bulkhead) to my pump. How effective it is as a 'spark suppressor' I have no idea - it was fitted years ago by an 'old-time' mechanic, so I assume he knew what he was doing...............

[svenedin]

That is interesting about the spark suppressor. I have a normal capacitor fitted externally (to the bulkhead) to my pump. How effective it is as a 'spark suppressor' I have no idea - it was fitted years ago by an 'old-time' mechanic, so I assume he knew what he was doing...............

I had a go running the pump in the dark with the cap off. I couldn't see any sparks at all. It definitely works.

The spark arrestor (as supplied by Burlen) is actually a bi-directional transient voltage suppressor diode (TVS) with the code 1.5KE18CA. Burlen puts some insulation on the leads and solders on connecting tags and sells them for £10.73 inc VAT. From an electronics supplier they are around 40 pence........

https://4donline.ihs.com/images/VipMast ... 234799DDF0

Stephen

[geoberni]

Over the years, SU tried a few different styes of Diode & Capacitor to reduce arching/pitting of the points. Hence the different types of bulge you find on pump Caps.
These are both Capacitors, an earlier probably '50s type on the left and a later tech 80s on the right.
The Cap profile on the right was also used when they were fitting Diodes, so they can often be the Polarity sensitive ones.
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As Stephen says, the 1.5KE24CA 'Transil' Diode (basically a diode that breaks down to stop the arching, performing the same function as the Condenser on the Ign Points) is a lot cheaper than the SU version.
The first pump I reconditioned a couple of years ago I brought just the one from ebay for £2.99 inc shipping, which was cheaper than me driving a 30 mile round trip to my nearest electronics store.
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I didn't make as tidy an example of it as Stephen has done to try it out .
As Stephen says, the difference between the arching at the points with and without the Transil was remarkable.
Having done that Trial installation to prove it to myself that it is worthwhile, next time I'm near an Electronics retailer, I'll call in for a packet of them.
I have a small collection of 4 or 5 SU pumps which I've brought off ebay, the first one was to give myself a spare, the others I'll sell on once I've got around to overhauling them.

Incidentally, it's pot luck what sort of Guide Plate, or weights are inside.
They started with the set of brass weights, then over the decades moved first to a single plastic/nylon guide plate, followed by a set of five 'figure 8' devices and have now gone back to the original concept of the brass weights.
I was on the phone to Burlen a couple of years back about their overhaul kits and asked why the kit now had brass weights like the original pumps, and the reply was the different versions of cheaper nylon/plastic devices they had used just weren't as effective, so they had gone back to the original design.

So my advice is the weights are best, but if you have one with the white nylon options, don't worry about it unless you want to buy a complete overhaul kit to get the brass weights.

[svenedin]

That's very interesting Berni. I've never actually seen a capacitor fitted or known why the stepped cap and now I know.

How do you finish the iron body? These rust and look bad but that in no way affects the working of the pump. If selling the refurbished pumps, the "natural" iron body finish is probably a negative to buyers. I have painted gloss black from a rattle can and that looks fine to me but the original finish looks like it may be a chemical treatment and is more matt/satin.

The aluminium alloy base section I wash in my ultrasonic cleaner. This does a good job but it won't remove heavy staining or discolouration.

The complete rebuild kits are rather expensive. In order to be profitable I think one would have to be a bit selective regarding which parts are replaced.

Stephen

[geoberni]

The Coil Casing I cleaned up and painted semi-gloss black.
The one originally on Basil was already painted a silver finish, so when I overhauled it I repainted it using an old tin of Hammerite silver exhaust paint. Apparently they don't sell it these days, in the little tin with the brush in the lid...

The spare one is natural Alloy base section; I think when I get around to doing the others, it will depend how they clean up.

[svenedin]

I have just done another one of these and I have revised the fitting of the TVS/Transil to something I think is simpler and more elegant with less strain on the component wires. I have also concluded that it would be difficult to fit a spark suppressor with a flat pump cap but it probably could be done.

Stephen

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[svenedin]

Another thought about the overhaul process. There is a rubber sealing washer that should be present above the nut on the terminal post. This sealing washer fits tightly against the inside of the cap when the nut on the outside is tightened down properly. In conjunction with a sealing band around the join between cap and body (which can be the SU sealing band or just insulating tape) the points are protected from dust, dirt and moisture. Cars that are used infrequently often have issues with corroded points, especially in damp climates. This may reduce the problem. I suspect it is often overlooked and the washer is not included in a rebuild kit. It will inevitably have gone hard or disintegrated on an old pump.

Part number: AUB 609

Stephen

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[svenedin]

Rebuild kits come in 2 variants: Pre-1985 and Post-1985. The diaphragm assembly is different and the kits are not interchangeable. It is very important to use the correct kit.

Pre-1985 pumps have a 2BA earth screw on the pump body (left hand pump). Post-1985 pumps have a 4BA earth screw (right hand pump)

Stephen

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[geoberni]

Yes, there is a difference in the Diaphragm, although I'm still not totally sure of the relevance; I've yet to find the time to investigate it fully.
The Post '85 has a ring which just seems to be there to better locate the spring in a central position....
Given the range of movement when operating and the compression of the spring, I'm not sure of the unsuitability of an incorrect one being used.
You'd think that if the post '85 is better because it keeps the spring in place, then you'd think it should be backward compatible. ...

I'll have to find the time to investigate further.
But best to use the right kit if you can.
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Images from the SU website, hence the watermark.

[svenedin]

Yes, there is a difference in the Diaphragm, although I'm still not totally sure of the relevance; I've yet to find the time to investigate it fully.
The Post '85 has a ring which just seems to be there to better locate the spring in a central position....
Given the range of movement when operating and the compression of the spring, I'm not sure of the unsuitability of an incorrect one being used.
You'd think that if the post '85 is better because it keeps the spring in place, then you'd think it should be backward compatible. ...

I'll have to find the time to investigate further.
But best to use the right kit if you can.
.
PUmp Diaphragm.JPG
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Images from the SU website, hence the watermark.

Fair enough. I haven't really investigated the differences either and I'm not taking the refurbished pumps apart to find out! Do let us know if you discover anything.

Stephen

[svenedin]

Some more stuff I have learned about these pumps.

If the inlet to the pump is blocked, the pump stalls with the points closed. This can lead to the coil overheating quite quickly. This can cause the "swamping resistor" to burn out. There is no way of knowing this has happened to the pump just by looking at it. Once the blockage is released the pump will still work but it will then go on to destroy points for evermore because the swamping resistor is destroyed.

I do not know when SU stopped using a swamping resistor or even if they did stop using it. Taking a coil out is not something that I would do. This might explain why some owners have enduring problems with a pump no matter what they do to try to repair it. Just a thought.

https://www.dbraun99.com/Dave%20DuBois/ ... _Myths.pdf

Stephen

[philthehill]

The answer then is to not to fit SU fuel pumps with electronics.
The old basic SU electric pump is a tough old beast and will put up with lots of misuse and will run for years even if it needs the occasional tap with a hammer.
I ran the basic non electronic SU fuel pump for many years feeding the twin HD4 SU carbs without problem but I now use a Facet red top fuel pump to serve the twin 45DCOE carbs as they need the additional flow but not pressure which is controlled by a Malpassi fuel pressure regulator with metal filter body.

[svenedin]

The answer then is to not fit electronic SU pumps.
The old basic SU electric pump is a tough old beast and will put up with lots of misuse and will run for years even if it needs the occasional tap with a hammer.

I'd take from the article, don't fit a filter before the pump and if a pump repeatedly destroys points it has probably been partially destroyed inside by previously overheating. Solution try fitting a Transil/TVS (very cheap), if this fails buy a new pump unless you happen to know how to replace the coil.

Stephen

[myoldjalopy]

With regard to the pump being 'fried', I note (as did Phil): " The results are even more severe if you have an all electronic pump."
Also: "To prevent unintended stopping of the SU fuel pump as a result of clogs, either on the inlet or outlet side, keep your fuel system clean and free from rust and sediment."
I suspect the latter in particular is a common problem with old cars. It happened to me out on the road once and I got home by blowing back down the pipe to the tank. To address the issue, I upgraded the old 5 gallon tank to a new 6.5 gallon one.