MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - MGA SU fuel pump inoperative

I am in the process of resurrecting a 1957 MGA for a new found friend. It had been sitting in a dry garage for about ten years. I did all the standard preliminaries over the last several weeks. Wednesday I bought some fresh gas and attempted to start it. Alas there was no encouraging ticking sound from the fuel pump. I tapped it sevearl times, which had worked on my own MGA in the past, but it was not being cooperative. I removed the tops from both carburetter float chambers and filled them up. The car started and ran well, for a short while.

Is there any hope for this pump, or shall I just order a replacement?
Chuck Asbury

Chuck,

My guess is that the flexible diaphragm is no longer flexible. Can you make a suction stroke by pulling on the operating rod and then releasing it and see if the spring can move the diaphragm for the output stroke?
If the spring can move the diaphragm is it enough to operate the points?
I would do this several times without the presence of an electricity supply. If it starts to free up then try the electrical power.
Caution. Do not have the exposed points operating in the presence of free gasoline liquid or fumes. It would be safer to remove the pump and use kerosene for pumping. Then you can use electrical power.

Mick
Mick Anderson

It is likely just dirty or oxidized points. You will need to remove the cover from the pump and clean them. The proper tool for cleaning contacts is called a burnishing tool, but you could try some very fine wet/dry sandpaper. If you try the sandpaper, use it dry and just do a few light strokes. You want to just remove the oxidation without damaging the metal points.

I had a brand new pump that did the same thing after sitting for only 2 years. A few strokes of a burnishing tool and it has worked fine ever since.

Jeff Schultz

Chuck - Start by cleaning the points, but you will need much more than a burnishing tool - ten years of film build up will need to be scrubbed off the contacts. Remove the upper points by loosening the 5BA screw at the back end of the blade and slide it out and scrub the contacts on a fine sharpening stone or a piece of 400 grit sand paper on a flat surface (I use the sole plate of an old flat iron). The lower points are a bit harder to clean. You will need to remove the two mounting screws from the pedestal and very carefully fold the pedestal back around the pivot pin at the back of the lower toggle until you can get a small sharpening stone or 400 grit sandpaper wrapped around a flat rod and scrub them until they are bright and shiny. If this doesn't get the pump running for you, you will need to have the pump rebuilt. Go to my web site at: http://homepages.donobi.net/sufuelpumps/ click on links and you will find list of people in the US who rebuild SU fuel pumps, any one of them can get the pump back into good condition for your friend (I am out of the picture until after the first of October). Cheers - Dave
David DuBois

I agree with Jeff and David that when an SU pump fails to operate the first thing that you do is to clean the points.
However, I have found that the points deteriorate more when in use than when in storage. In storage the diaphragm hardening seems to be the worse problem.
The suction stroke is fairly strong as it is powered by the solenoid, but the output stoke is only powered by the light spring which sets the pump pressure.
This hardening of the diaphragm also occurs in mechanical fuel pumps in storage, which of course do not have electrical points.
If you replace a diaphragm remember that it must be held in tension (stretched position) while the locating srews are tightened.

Mick
Mick Anderson

Mick is correct regarding the diaphragm becoming hard over time, and I should have said the next place to look at would be the diaphragm (I have seen far more bad points than diaphragms). The one thing that I have to disagree with Mick on is stretching the diaphragm. That was undoubtedly required at one time many years ago, and of course the information is still in the original manuals. However, materials used in the diaphragms produced today, stretching is not necessary and in fact is discouraged. Cheers - Dave
David DuBois

Mick is correct regarding the diaphragm becoming hard over time, and I should have said the next place to look at would be the diaphragm (I have however, seen far more bad points than diaphragms). The one thing that I have to disagree with Mick on is stretching the diaphragm. That was undoubtedly required at some time many years ago, and of course the information is still in the original manuals. However, materials used in the diaphragms produced today, stretching is not necessary and in fact is discouraged. Cheers - Dave
David DuBois

Well today I finally got to play with the MGA again. I removed the pump, which appeared to be nearly new but is at least ten years old, and removed the cover from the points. I could see that one side was slightly pitted, not bad at all. When I removed the points that are mounted on the flat spring, I was surprised at how much crud I was able to get off of them with the wet or dry (used dry) sand paper. The other pair was a bit harder to get at for sanding, but I was still able to sand them. I didn't ramove them frim the pump. After reassembly I attached the pump to my battery charger (+ to earth) and turned it on. It clicked to life with just two amps.

I let the pump refill the carburetters and hit the starter. The car started right up, and seems to be running well. If I have time, I will take it on the streets on Monday.

Thanks very much for your help in this matter. It was quite a simple straight forward repair.
Chuck Asbury

If it hasn't been driven for 10 years, there are some things you should do before you drive it. These are just the things that got me, I am sure there are other things to check.

First, check out the brakes very carefully. If it still has the plain steel brake lines, they will rust from the inside out and could be very weak. Mine split wide open. Don't know if there is any way to check them out, but make sure the parking brake is working just in case the hydraulics fail.

Also, disconnect the speedometer cable. The grease in the speedometer can dry up and cause the gears to stick. Driving it like that can ruin the fibre gear which is not made any more. You can try turning the speedo by hand to see if it is locked up(use a small screwdriver).

Jeff Schultz

David I was hoping you could recondition 2 pumps, one for myself and one for a friend of mine. I was hoping I could organise some way of doing this and getting the reconned pumps from you when I am in Florida next October/ November.
Could this be possible do you think?
Bob (robert) Midget Turbo

Bob - I am not doing any pumps during the summer (my time to get home projects done). I start up again the first of October. E-mail me at the above address or go to my web site at: http://homepages.donobi.net/sufuelpumps/ and use the address for me on that and we can perhaps work something out. Cheers - Dave
David DuBois

Jeff, I had not given a thought about the speedometer. I have yet to drive the car as it has been extremely rainy here all week. Maybe Saturday, after I check out that speedometer. With just under 33K actual miles, I don't want to mess it up.

The brakes are up, but I suppose the lines could be bad. I doubt they've ever been replaced. I'll try giving them a extra hard stomping or two to see if they are likely to rupture. If they don't, well do our test drive.
Chuck Asbury

This thread was discussed between 12/06/2008 and 20/06/2008

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.