Fuel Pump Strip Down and Rebuild

My fuel pump looked a mess......

Fuel Pump - 7 June 2015

Even though modern, reproduction fuel pumps are readily available, I was keen to try to retain my original and distinctive 'SEV-Marchal' pump. I had re-plated the top cover back in 2015, but have only just got to the point where I need to be refurbishing and refitting the fuel pump. Instructions for rebuilding can be found at Operation DX. 173-3, which can be found in section 2 of volume 2 of Citroen workshop manual 814.

Orientation of the Two Pump Valves

The upper and lower body were unscrewed. The seal under the domed top cover was very, very carefully prized off the pump body and feed tube using the edge of a stanley knife blade, allowing access to the two valves within the chambers. These are orientated in opposite directions and I took a reference photo. Despite what step five in the Workshop manual suggests, I was able to remove the valves. I planned to use a socket to drift the valves out, but found a socket too chunky for what looked to be quite delicate valves. Searching around I found that the 22mm end of a copper plumbing pipe reducer was a good fit for the diameter of the chambers. The valves were then easily removed. The key is to put your chosen tool in the dished side of the valve, so that the sharp edges of the valves are pulled - rather than pushed - through.

Moving on to the bottom half of the body, the cam that operates the pump was released by carefully removing one of the tiny locking circlips from it's groove in the cams spindle. The cam was then unhooked from the base of the operating rod inside the lower body, allowing it to be pulled out -  freeing the spring within. There were also two spacer washers that fit inside the body on the spindle.

Soldered Bolt on Diaphragm

The bolt holding the diaphragm assembly together is locked with solder. I suspect that this is to set and maintain the correct operating force (pumping force) on the diaphragm spring. With this in mind, I marked the orientation of the bolt to the diaphragm before unsoldering it, and made a note of how many turns it took to separate the bolt from the operating rod.  (Note: In Step 3 of Operation 173-3, the diaphragm and attached rod are removed as one - without removing the soldered bolt).

The small black rubber cup at the cam end of the operating rod was as hard as rock. In fact at first I wasn't even sure it was rubber. It was the workshop manual that confirmed it was. These parts aren't obtainable as spares and so it was make or break. I left the rod and cup soaking in a mixture of wintergreen oil and isopropanol alcohol for a couple of days*.

Wintergreen oil is the smell you get in Deep Heat. It is a very strong smell. People tend to either love it, or loath it. I left my parts soaking in the green house so that I didn't stink up the workshop! Personally I like it - but not in these quantities and strengths. I accidentally getting some of my mixture on my hands: the smell travelled everywhere with me. I poured some in a saucer. Despite washing it thoroughly first, dishwashing the saucer caused the whole dishwasher load to stink!

Miracle of miracles, after a couple of days the rubber cup began to soften with no signs of swelling. I left it a few more days but didn't want to push my luck. The pump diaphragm was showing signs of fatigue. Removing the metal plates that sandwich it, I gave it a bath in my wintergreen mix. Again, this had the effect of softening it.

Components of My SEV-Marchal Fuel Pump - 16 December 2017

With the valves removed and the rubber parts salvaged, the two halves of the body were taken away for vapour blasting - as was the metal spacer plate that fits between pump and engine. All the parts were then carefully cleaned before re-assembly.

The diaphragm sandwich was reassembled and the bolt tightened as per the note made during removal and then re-soldered. Reassembling the cam on the operating lever was fiddly because of the need to also align the spindle spacers in the body. I VERY carefully teased the circlip back on the end of the spindle and, after cleaning the end with alcohol, sealed it on with a small blob of Araldite.  The valves were refitted - again using the copper water pipe reducer - and the body re-assembled. 

Rather nervously I followed the instructions in step 12 of Operation DX.173-3 and tested the pump by emerging it in petrol and putting it under a little pressure to check for leaks. It passed muster. After draining, the spindle and cam were lightly lubricated with clean engine oil and I fitted the pump to the car. The smell of wintergreen oil dissipated (after about a week!).

Fuel Pump Fitted

* CAUTION: there are different compounds of rubber and there is a danger that some may react badly to soaking in wintergreen oil and/ or alcohol. This may take the form of swelling (growing alarmingly in size) or the surface dissolving (black sludge rubbing off on your fingers). If you are tempted to try this but cannot afford to risk ruining a piece, then you would be better off finding another way.