Mk1V SU Fuel Pump


I am rebuilding a pair of pumps from parts I have acquired over the years. One of the SU marked rubber diaphragm has a sheet of thin clear plastic covering the the rubber on the fuel side of the diaphragm. It appears the plastic & rubber have been punched out at the same time including the holes & then riveted to the spindle. Does one keep the plastic or remove it prior to assembling the pump? It just seems strange that you would remove it with the possibility of damaging the rubber diaphragm.

Regards Peter

Leave it on thats how they are.

I also left the plastic on mine. The original pumps in my '74 XJ12 had plastic on the diaphragms. I assumed it was a later improvement.

Thank you Gentlemen, I shall leave the plastic intact when assembling the pump.

On another matter with setting the diaphragm up, the 40’s Mk1V workshop manual says the diaphragm has to be stretched before tightening the six screws holding the coil to the body of the pump by removing the hinge pin of the rocker unit. In the 50’s the MG T series workshop manuals says the diaphragm is stretched by wedging match sticks under the rollers of the rocker unit, passing a current through the coil & then tightening the six screws. In the 60’s the BMC workshop manuals say nothing about stretching the diaphragm, just tighten the six screws evenly.

Anyone have any thoughts why the procedure changed over the years & which is the best method?

Regards Peter

When I rebuilt the SU pumps in my S11 XJ6 I just screwed everything together, making sure the diaphragm clicked over when the points were pushed.

Me too, maybe that’s the advantage of the plastic sheet.