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SU fuel pump


jagnut66
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Hi, 

I am in the process of renewing the SU fuel pump (AUA66) on my Morris Minor, so that it is ethanol proof (or should be.....).

That said I have bought a kit to refurbishing the old one. It still works but will be too old to have an ethanol resistant diaphragm inside. The kit is comprehensive, so I can renew anything else I feel needs it.

I was then going to keep it as a 'good known spare'.

However, as I am going to replace the fuel line from the tank anyway with a Kunifer / ethanol proof hose one, I am now thinking that it would be a good opportunity to upgrade the Herald, which has the standard mechanical pump at present.

So what do others think, what are the pros and cons? 

Mechanical vs Electrical?

I assume the fitment of a mechanical pump was a cost cutting exercise originally?

Best wishes,

Mike.

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  • jagnut66 changed the title to SU fuel pump
13 minutes ago, jagnut66 said:

I assume the fitment of a mechanical pump was a cost cutting exercise originally?

Why would you assume that? No, nothing to do with cost and all to do with reliability or habit. Austin used electric pumps, Triumph used mechanical ones. In the day, you never saw a Triumph driver open the bonnet to give the fuel pump a sharp tap with a hammer to make it work. Also, a mechanical pump can deliver more fuel at high revs, less at idle, while an electric one is fixed capacity.

I put an electric pump on my Vitesse because (due to an engine change) the mechanical one I had no longer fitted. I had so much grief from that electric pump that I bought a second-hand "failed" pump from a 2500S and refurbished it. The Vitesse now runs way better on that pump than it ever did on the electric one.

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16 minutes ago, NonMember said:

 Austin used electric pumps, Triumph used mechanical ones. In the day, you never saw a Triumph driver open the bonnet to give the fuel pump a sharp tap with a hammer to make it work.

:) True

I was amazed last week when looking over a Morris Minor restoration to see an electric fuel pump. I never knew they were so... modern...

I'm waiting to see how the introduction of 10% ethanol affects our mechanical fuel pumps, if at all.

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41 minutes ago, NonMember said:

Why would you assume that?

It was simply a question, hence the question mark.

But thankyou for the answer, as that satisfied my curiousity anyway. As you probably know, back in the day allot of manufacturers looked to save money wherever they could, hence the way the question was worded, thinking that a mechanical pump would be a cheaper option than an electrical one.

Your remarks on reliability and fuel delivery answer the other question I raised (pros and cons).

22 minutes ago, Colin Lindsay said:

I'm waiting to see how the introduction of 10% ethanol affects our mechanical fuel pumps, if at all.

That has crossed my mind and is a 'plus' for the mechanical pump.

If there are no arguments 'for' the electric pump then I will leave it 'as is'.

Best wishes,

Mike.

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In general mechanical items are inherently more reliable and efficient than electromechanical items. The first because theres fewer components to fail (fuses, cables, connectors, windings, switches etc) and the second because youre not converting from mechanical energy to electrical and back again.

As for E10 in mechanical pumps I think the most likely problem will not be the diaphragms or valves but the rubber seals used on the filter/lids...

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13 minutes ago, johny said:

As for E10 in mechanical pumps I think the most likely problem will not be the diaphragms or valves but the rubber seals used on the filter/lids...

So one of these kits will be required then?

https://www.googleadservices.com/pagead/aclk?sa=L&ai=DChcSEwjR-8T27uzyAhWO0-0KHeERDr0YABAHGgJkZw&ohost=www.google.com&cid=CAESQOD2UWSaT9inzmCv__NXU00tJkqJJACUJzmyLkQGVZr7qjRLKfsPAbkY5AIOq_6X0Kr7afmGV_EEjrkQHVdy_js&sig=AOD64_0JhHq9OWouWZiV_arOQI7BaE17cQ&ctype=5&q=&ved=2ahUKEwjP17z27uzyAhWQilwKHY9sB5sQ9aACegQIARBE&adurl=

Best wishes,

Mike.

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On 07/09/2021 at 14:19, johny said:

However the risk with pattern pumps is that they can produce too much output pressure... 

Though, this can be overcome by using the original spring?, cam lever (if not correct?). No experience, though heard it mentioned on here, I think?

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  • 2 weeks later...

The fuel line is now replaced and the fuel pump refurbished.

However I think this was a case of just in time. 

The old steel fuel line snapped like a dry twig when I tried to fold it up to put it in the bin bag. The original joining rubber sections had set hard and welded themselves to the pipe, which was just as well, as they had all been attached as a 'push fit' item, with no fuel line clips used to hold them in place at all, anywhere on the line, from tank to pump (picture 1 below). I'm amazed it never leaked.

The pumps diaphragm was also on its last legs, with no flexibility in it at all, the only thing keeping it plyable was the fuel itself. 

Anyway I took that off the engine, cleaned it up, replaced the diapragm, the little filters and the rubber seal for the lid. I cleaned up the top gauze filter, which isn't supplied new in the kit anyway. 

I also cleaned out the body of the pump which was full of crud. The car seemed to be running happily but I can't help wondering how much longer that would have lasted.

The mechanical side of the pump (apart from the diapragm) seems okay, the action seems good and free, so I just cleaned it up and put it back, with a new gasket, onto the engine block.

Of course with the new line and refurbished pump in place I was left with an empty line and a massive air lock between the tank and the carb, which I think the mechanical pump by itself would have struggled to overcome. I did try turning it over but to no avail.

Then I had a lightbulb moment, I rigged up my spare Moris Minor electronic SU fuel pump and used this to suck fuel back through the line, all the way to the carb. then screwed the pipe back into the carb and bingo! Houston we have ignition!

Anyway, I also have some spares left over from the kit (picture 2 below), which I assume relate to the mechanical side of the pump, which I didn't find reason to dismantle.

I also have a (now) spare screw on nut (top left in picture 2). This was attached to the stud on the bulkhead side of the fuel pump, slightly obscrured by the pumps priming lever. I have replaced it with a normal nut, which being smaller (shorter) is easier to get a small socket onto for removal and replacement.

Was this an original fitting, or just something someone has used because they lost the original nut at some point?

Anyway, I think the point of my writing this is as a warning to all those out there running their cars on 50 plus year old metal fuel lines and rubbers -- it might be worth you checking and replacing them and, for the price of the kit (link below), servicing your fuel pumps too..............

https://www.ebay.co.uk/itm/133818427423

Best wishes,

Mike.

 

Picture 1.JPG

Picture 2.JPG

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On 08/09/2021 at 20:25, johny said:

The spring is the component that determines the output pressure but replacement pumps look quite different so not sure they'll accept or work properly with another spring...

I successfully mated the top half of a new metal-top pump (new, as in I bought it 7 years ago) onto the lower half of my old glass-top AC Delco one at the weekend - dimensions where they meet are identical and no problems at all with leaks or fuel pressure. I'd surmised they should be compatible as the diaphragms are the same.

Gully

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