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MG MGB Technical - Fuel pump - smoothing chamber pressure tests

I am refurbishing a fuel pump, type AZX 1307 later type, that stopped and which would pump two thirds of a pint in 30 seconds and then stop. Not much use.

The pump has been off the car for 3 weeks and effectively dry of fuel. Today when removing the ’top hat’ delivery smoothing chamber, fuel ran out implying that the diaphragm, washer, O-ring combination leaks fuel into the air space above the diaphragm in the ’top hat’, but not to the outside world.

In the WSM it states that replacing this diaphragm should only be undertaken if “…the necessary equipment for pressure-testing is available.” - in section D.3 point 8 Body and Valves (in AKD 4957 5th edition).

I can’t find any other information on the equipment or tests. Is there an opinion on this or is the test such that it should not leak?

The Burlen Fuel systems state much the same, but no detail on the test.

https://sucarb.co.uk/technical-electrical-fuel-pumps-reassembly

Any advice would be welcome.

Best wishes,

Richard.
Richard Thompson

Yeah-
forget the tests, if there is fuel on the top side of the diaphram it's leaking through the diaphram
If the seal on the shaft is good the fuel gradually builds up on the wrong side of the diaphram via the leak and is trapped there stopping the diaphram from getting to full travel and the pump stops
New diaphram will fix it
willy
William Revit

Bit late now for you, but for others once the pump body has been separated from the solenoid housing don't touch either of the chambers on the pump body as there is nothing in there.

If they are leaking, or you have removed them, then you will have to replace the gaskets. A pal did that and the new gaskets from Burlen did not fit. They said there were various bodies and they didn't have gaskets for all of them, and he ended up having to get a new pump.

Those chambers are fuel-side but contain air and act as dampers, which is why the pump has to be orientated in a particular way when running. This is nothing to do with fuel on the solenoid side of the diaphragm, which does indicate a ruptured diaphragm. There can be other reasons why pumps stop working after a while, an original SU AZX1307 is a points pump so they are the most likely cause of not working and should be the first thing that is looked at. There are copies from other manufacturers but using the same part number with blue cases instead of black that are electronic, again it's the electrics end that should be investigated first.

paulh4

The electrics are all sorted and the points flick over as expected. I had to clean and polish up the points and adjust the .035” & .090” clearances on the rocker to account for points wear. There's not much left of them though.

I’m reworking the pump using the old parts as practice run before buying an SU refurbishment kit that includes the smaller diaphragm, gaskets and O-ring for the delivery smoothing chamber. Hope the ones supplied fit, and thanks for the warning that it may not.

Maybe a call to Burlen on the fit and the tests may be the way forward.

Richard.
Richard Thompson

This thread was discussed between 10/03/2019 and 11/03/2019

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