Fuel Pump Tech Tips


Hurricane engine

Fuel Pump Mounting Spacer

The fuel pump mounts on the left side of the Hurricane F-134 engine, and the original two-stage (dual action) pump also functions as a vacuum pump, helping to power the windshield wipers. The rocker arm of the fuel pump extends into the engine and rests on an eccentric on the rotating camshaft.

More than one person over the years has asked on the CJ-3B Bulletin Board about the function of the thin spacer (20K JPEG) between the fuel pump and the engine block, and whether it is necessary.

Ken Bushdiecker ("Oldtime" on the Bulletin Board) provided the answer, and some background information on fuel pumps in Willys 134 applications. -- Derek Redmond

Oldtime: The CJ-2A front engine support was changed on the CJ-3A to allow clearance for the larger dual action fuel pumps. The CJ-3A used the AC 9353 dual action fuel pump without glass fuel dome. (See CJ-3A, CJV-35/U, and M38 Fuel pump information and rebuilding on the CJ-3A Information Page.)

This same front engine support was used for all later 134-powered CJ's and DJ's excepting those equipped with Delco Remy generators. The CJ-3B, CJ5 and CJ-6 all used AC 4032, AC 4080 or AC 4693 fuel pumps. All of those pumps were orignially equipped with glass fuel domes. The DJ's used AC 9716, AC 4698 or AC 9562 fuel pumps. Hurricane SW and PU used AC 9562. The FC-150 used AC 4080.

Normally the AC model number is found stamped onto the forward edge of the mounting flange (the narrow edge.) Many but not all of the various pump components can be interchanged between various AC pump models. Pumps may be a mixture of various components.

Note: AC got away from using glass domes by the mid 1960s. By the 1970's AC pumps were no longer repairable. You may note that the so called "glass dome" is actually an inverted fuel sediment bowl. For whatever reason these AC sediment bowls are inverted to fit on the Willys engines.

Several different pump rocker arms were factory installed into these various pumps.Some pump rocker arms are longer than others. Some pump arms have flat followers (bearing surface) and some have concave followers. See below:

Concave surfaceFlat surface

Is the shape of the rocker arm follower flat or is it concave? If concave one needs to measure the distance to the center of the follower's cavity. The center of the concavity should be 1-1/4" from the mounting flange. If further the .14" (just over 1/8") thick mounting spacer will be required.

.14 inch spacerIf flat you do not need the .14" thick mounting spacer, but you may decide to install it to slightly reduce pump volume or pressure. If the spacer is used on a pump the diaphram will not travel up and down as far. This shorter diaphragm travel will also slightly increase the diaphragm's longevity. The spacer's effect upon fuel volume is really of little to no concern because the Carter YF on a Willys 134 has a notably restricted inlet orifice (.077").

The effect of the spacer on pressure is pointed out in the L6 226 engine section of the Mechanic's Manual, Form No. SMM-1001 (1956), which states on p.97, "High fuel pressure may be corrected by adding gaskets between the pump body and engine block." I searched all my other fifteen service and mechanic's manuals, including the industrial engine service manual, and I find no other references like that. But yes, the 226 pump works virtually identically to the 134 pumps, so it's valid information. Thanks to Bob Westerman for that reference.

So I reexamined how a fuel pump operates. Fuel pressure is created by spring pressure. The rocker arm pulls the diaphragm down, against spring pressure, drawing fuel into the pump. As the camshaft rotates the rocker arm releases tension on the diaphragm pull rod. The spring pushes the diaphragm up pushing fuel out of the pump and supplying the pressure. Fuel pressure is directly proportional to the spring pressure. If the spacer is eliminated, the rocker arm travels too far, compressing the spring too far, and therefore can cause too much fuel pressure. It is the diaphragm spring that effects the pump pressure, not the check valve spring. The stiff lever spring is only to keep lever pressure on the cam lobe.

Take a look at the rocker arm. Is the pump arm composed of laminated steel plates, or is it a forged arm? Laminated arms are riveted together. That is typical for the AC 4032 and AC 4080 model pumps. Note the rivet that is located near the center of the bearing surface.

The center of that rivet makes a good reference point for measurement. Measure from the mounting flange surface to the center of that rivet. That distance should be very near 1-3/16". You will only need a spacer if your pump arm measures more than the desired 1-3/16" distance. The exact distance from mounting flange to center of the follower is not a big concern if the rocker arm follower is flat. Yet the distance is critical to pumps having a concave follower.

AC 4693
Note: the AC 4693 (left) mainly but not always uses a unique sliding pillow block type of follower. The AC 4693 should use the .14" thick mounting spacer.

To determine if your specific pump needs the spacer, one should verify the pump model number and the specific design of the rocker arm.

A further note: all these fuel pumps function both as fuel suction pumps and as fuel pressure pumps. This explains the mounting height relative to the fuel supply and the YF-938 carburetor.

Military spacerTodd Marquart commented: "I have an M170 with the military fuel pump and spacer. I believe the spacer on the military Jeep is required to make the pump fit correctly. The military spacer is very thick when compared to the 2-3mm spacer."

Greg responded: "Wow, what a much-needed answer. Proves my point about manuals not being written for folks like me; none of this extremely vital stuff is covered in my manual. No wonder some people on the forum have recently written posts about the surprising difficulty in installing a fuel pump.

"Two questions (and the answers are probably obvious to those who have done lots of mechanical work on their Jeeps):

1) Do I use a gasket sealer on the fuel-pump gasket? On both sides of the gasket? Or, no gasket sealer on fuel-pump gaskets on Hurricane 134s?

2) Between a "new" fuel pump (Carter M2846 with no glass bowl) and a "rebuilt" fuel pump AC 4032 (with glass bowl), which one of the two fuel pumps could be considered to be superior to the other and why? (Yes, it seems almost obvious, but I don't know all the facts.)"

Oldtime: 1) I suggest you apply a thin film of sealer to the block side of the gasket. I suggest Permatex Ultra Black because of its oil resistance. Do not apply sealer to the pump side. In this way you can remove the fuel pump at a future time and re-use the same gasket as it should adhere to the block.

2) I always prefer genuine NOS or rebuilt original parts, also OEM parts.

Fuel pump parts

Fuel Pump Reassembly

As mentioned above, the AC fuel pumps with glass bowl can be rebuilt. Rebuilding kits are available from Jeep parts dealers. Correct reassembly is critical.

John King: My pump is back together. Below I have listed my 'tips' on reassembling the AC dual action pump. I am not a rebuilding expert and this is the first one I have done. So consider these beginner tips. I'm sure others who have more knowledge and experience have different and/or better techniques. I specifically list the details of dealing with the two diaphragms.

The first two steps are critical if there is any delay between the time you take it apart and put it back together, like me. I was just lucky I took them.

1) Take pictures of the three areas where the check valves are so that you know the proper orientation of the valves.

2) Take a picture of the fuel cap to document the orientation of the fuel ports. The cap screw holes are such that you can easily attach the cap incorrectly.

3) You can use properly sized sockets and a rubber hammer to seat the check valves and oil seals. Do not forget to install the paper gaskets.

4) After the oil seals and check values are in are you are ready to assemble the diaphragms, take some time to carefully examine the diaphragm shaft ends and the action arm. The vacuum diaphragm shaft attaches to the end of the arm while the fuel diaphragm attaches to the center of the arm. With these three pieces only, carefully examine how they attach. Determine the angle and path they must take to attach and make a mental note. You will basically have to perform this operation in limited space, under spring load( fuel), with little to no visibility.

5) Lube the end of the vacuum shaft so that it will easily slide thru the oil seal. You don't want to damage the seal.

6) Insert the vacuum diaphragm shaft thru the oil seal. Align the seal which will in turn align the shaft properly. Insert the action arm into its opening, leave out the arm' spring for now.

7) Using what you learned in step 4 attach the vacuum arm. You can manipulate the arm and the diaphragm a bit to get it connected. Pull on the center metal piece of the diaphragm to ensure connection.

8) Lube and insert the fuel diaphragm, this one is spring loaded so you'll have to apply constant pressure to keep the shaft in the opening while you attach it. Manipulate the arm and diaphragm as necessary, taking care not to detach the first shaft as it can slip off easily and you'll have to start over. Verify the connection the same way but be careful as the fuel one is spring loaded and can detach and fly into your face or even worse, your spouse's face. In which case you've got a boatload of more trouble than a broken fuel pump.

9) Once both are attached, use something long and narrow to temporarily secure the action arm into place – I used a long narrow punch. You want something narrower than the action arm shaft because you need a little play in there.

10) Install the fuel cap (first because it is spring loaded). Remember to check the fuel port orientation. You don't have to tighten it all the way down or use all the screws, you're just trying to secure them enough so that the shafts don't dislodge from the arm. Do the same with the vacuum cap, it only goes on one way unlike the fuel cap.

11) Install the action arm spring. You'll have to have a little patience to manipulate it properly, but the temporary shaft should provide enough play to seat and load the spring using some screwdrivers. I used a small one to seat it and a larger one to load it. I chose to do this at the end as trying to keep the spring in place while installing the diaphragms would require an extra hand.

12) Secure caps completely.

13) Complete the job by installing the action arm shaft with some sealant. My replacement shaft was not tapered like the original, I'm cleaning up the original and using that.

This was my technique. Some more experienced guys may point out some flaws in my process and please feel free to do so -- I don't want to lead anyone astray.

Oldtime: Very good instructions, John.

Thanks to Oldtime, John, Greg and Bob W. for their contributions. -- Derek Redmond

See also Fuel Line Tech Tips.

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Last updated 29 November 2016 by Derek Redmond redmond@cj3b.info
All content not credited and previously copyright, is copyright Derek Redmond