Rebuilding a Single Action Fuel Pump

49 Custom · Sep 21, 2012

The Story (skip this if you want to go straight to the tech)

A few months back I began to have trouble with my '49 Ford: it would would stall out under load in the most inconvenient places (the highway, intersections, etc.). I suspected it had to do with fuel delivery so I began sorting through the entire system, starting with my rusty fuel tank. It had been shedding flakes of red iron for years and I knew I would have to eventually deal with it, but I kept putting it off. Now with sediment building in the bowl of my fuel pump, I decided to replace the tank. Then I rebuilt the carbs (which was a good thing as there was plenty of red sand in the fuel bowls of my 94's which could have clogged the jets).

So I thought my troubles were over. I took the '49 out for a drive and got about a mile from home when the same problem occurred: she stalled under load. I thought about it a little more, read a little more, and watched the engine run in the driveway. Air. Air was bubbling into the fuel pump. That most likely meant one of a couple of things: either I had a leak in the line heading to the pump or there was a failure in a seal in the pump, itself. I checked the line from the tank and replaced the rubber parts. Ethanol can do awful things to rubber and though I had mostly steel lines, I had two spots where I switched to rubber to allow for flexing.

This left the fuel pump. As it also has rubber parts, I knew I had to check for a torn diaphragm, damaged valves, or a bad seal.

The Tech

Here's a typical single action mechanical fuel pump. The main parts from left to right are the fuel bowl (input), the body top and bottom, and the fuel pump stand. Note, when rebuilding these pumps it is not necessary to remove the stand.

First, do a general inspection. Are there any obvious leaks or missing pieces? Next, either draw or scribe a mark across the top and bottom halves of the body so that when you reassemble the pump everything is oriented the same way as when you started.

Having removed the fuel bowl and pump stand, unscrew top and bottom of the body to reveal the diaphragm.

To remove the diaphragm, press it into the bottom of the body and slide it away from arm. There is a little hook holding it in place so it may take some wiggling to slip the diaphragm free. Once the diaphragm is off, the main spring will fall off, too. (Note: the arm in this picture is actually upside down.)

The arm can be removed by tapping out a pin in the body (look ahead a couple of pictures and you can see the pin disassembled). I used a nail punch to tap it out with a hammer while resting the body against a block of wood. When the pin is out, the arm will pop out, along with its spring.

The top part of the body is much more straight-forward. Pop out the one-way valves and their gaskets. Make note of which way they face, though, because if you install the new ones the wrong way, the pump won't work! The new gaskets and valves simply press into place.

Looking at the lower half again, the new arm is installed the same way it came out. Align the pivot hole with the holes in the body and then tap the pin into place. (The old arm is shown below for reference.)

The new diaphragm hooks to the arm by pressing it and the main spring against the body and sliding it toward the arm. Keep in mind that the slot on the diaphragm has to line up properly in order to get the two linked.

The smaller arm spring easily snaps into place.

Now align the top and bottom halves of the body using the reference marks you made earlier. Re-install the screws in a star pattern carefully assuring that the diaphragm doesn't get pinched.

Place the brass filter into the lid of the fuel bowl and then press in the gasket.

Replace the glass bowl (and the pump stand if you removed it) and you are all finished.

Notes

I used a kit that was apparently manufactured for Toyota/Nissan: the parts fit perfectly and are apparently developed to resist ethanol damage.

It is definitely easier to reinstall the pump with the stand already attached to the block. The small cup on the pump arm must sit over the rod that projects from the block.

Total time for the rebuild was about an hour.

Once installed, check for fuel leaks!

If the old diaphragm was torn, there is a possibility that fuel may have run into the oil pan. Consider replacing all of your oil if this has happened.

Conclusion

My fuel delivery system has now been almost entirely rebuilt or replaced (at some point I will re-plumb the steel lines and eliminate the rubber segments). The pump is no longer bubbling with air; but I have yet to put the engine under load.

I hope that these simple fuel pumps are no longer a mystery and that you consider tackling a rebuild before a complete replacement. It certainly costs less and you gain a better understanding of your ride.

All the Best,
Stefan