AC FUEL PUMP SERVICING

After the roadside assistance given by Glyn Llewellyn to change my broken fuel pump, I dismantled my fuel pump to repair and service it. Having bought a service kit for my Type U fuel pump from www.vintageandclassicspares.co.uk, I spent a little while cleaning everything in petrol with a light brush. I cleaned the filter gauze, although kept it as a spare and fitted a new one I’d bought. I cleaned the fuel inlet sediment chamber and all of the base. I didn’t find how to remove the pump lever, but there was no slack in it so I was happy this was OK. There are many different fuel pumps around, but the Austin fuel pumps have a longer pump lever arm, which is normally marked with 856955 with the correct lever ending in a double digit! The lever arm on my pump looks to have been fabricated from plate and doesn’t have any markings though.

I removed the metal retainer for the fuel pump seal in the base that the diaphragm pull rod moves through, by levering it out carefully from the top with a screwdriver. I fitted the new rubber fuel pump seal in the base that the diaphragm pull rod moves through and fitted the metal retaining disc back over it and using an old screwdriver, re-staked the casting face to retain the disc.

For fitting the fuel valves in the upper body, there is a paper gasket (on my Type U, called a spectacle gasket), and it is recommended using a thread locking/retaining compound on the screws for the valve retaining  bracket. I used Loctite 222, which I had available.

It appears there is a good variety of shapes for the valve retaining bracket – mine was H-shaped but others are triangular. Similarly the valve gaskets vary in shape and size.

Refitting the gauze and making sure this was sitting within the body and sub-flush, I fitted the domed cover with a new washer and fitted the retaining screw with a new fibre washer. It is important not to tighten the dome retaining screw on the top too much because it is easy to strip the thread in the casting body. Alternatively, a stud can be fitted in to the body fully, preventing the thread from stripping and a nut used outside to retain the domed cover. My pump had the screw, which I carefully tightened and I retightened it slightly a few days later after it had been run on the engine.

Fitting the spring and diaphragm is a bit tricky and probably needs a few attempts and, ideally, about 6 hands! Aligning the pull-rod end with the slot in the base and noting the position of the diaphragm to know how far to turn in, carefully slide the pull rod through the new rubber oil seal and push down on the diaphragm against the spring pressure and turn it through 90 degrees. Pushing the pump lever away from the pump body will reduce the spring compression needed. The diaphragm pull-rod will be retained and locked in. Align the diaphragm holes around the edge approximately with the screw holes in the body. Fit the two halves of the fuel pump together and fit the six screws very loosely. Pull the pump lever towards the body to depress the diaphragm to the most stretched position and then tighten the 6 screws uniformly tightening in turn screws opposite each other. Once assembled, moving the pump level should result in a croaking noise.

Fit a new paper gasket to the crankcase mounting face if needed and slide the pump lever pointing upwards into the hole on the crankcase ensuring the lever is just inside the crankcase and outside the camshaft. Once bolted in, turn the starter handle by hand a few times to ensure the pump lever is in the correct position and the engine doesn’t lock up. Refit the fuel lines and, hopefully, all will work when started.

When I examined the removed diaphragm of my pump, it appeared intact and the only thing I could find wrong with the pump was possibly one of the fuel valve fibre washers had moved slightly sideways and wasn’t seating properly and therefore not sealing correctly. Having fitted the pump, all seems to be working as expected with no fuel or oil leaks. Although the three pumps I have are all marked as ‘Type U’, they are each slightly different, so if you are servicing your pump you may need to research the parts needed. For example, my pump didn’t have a drain screw in the upper fuel chamber to allow debris to be removed, which most seem to have. Happy motoring. Nick Kidd DA7C