Early B Fuel Pump Rebuild

[David Grubbs]

I've rebuilt my early B fuel pump. Now that I have it screwed tightly back together, the rocker arm seems really tight. I can barely move it when I push on it. Can that be right? I've disassembled and reassembled it half a dozen times.

[David Grubbs]

My apologies for distracting more than fifty viewers with this. I reassembled the pump with the original diaphragm to find I could operate the pump with my pinky. The original diaphragm is - well ... "flaccid" - comes to mind. There are even quarter inch high bulges on each side of the central plates. I suspect the pump hasn't been openned since the engine was assembled in 1960.

I'm shaken by the notion that I'm trusting other parts of similar vintage.

[Mike Wilson]

Not a distraction to 75+ of us but rather another issue encountered and resolved.

[Mervyn Hyde]

Yes David, I had the same issue with a small hole forming in the membrane. Luckily I had a new Pierburg pump still in its box and after checking that over, fitted it. I am rebuilding the original as a spare. After a couple a mishaps following the 'fix it when it breaks' approach, I am firmly in the 'replace it before it breaks' camp now for all accessories and peripherals.

[Dick Weiss]

David,

The diaphragm on the left is surely NOT flexible compared to the one on the right--I've seen worse, too.
The rebuild consists of applying some pressure on the rocker arm to pull down the diaphragm enough to contact the
face of the lower body before adding the top 1/2 w/the 6-screws and snugging it together.
As mentioned in the shop manual(s), the same procedure is used on the late (horizontal) fuel pump.

Dick

[David Jones]

Dick, Far be it from me to question your statement on the late fuel pumps but I have never seen anything to suggest the need to pretension the diaphragm on the late pump. I have always just assembled them and installed them. Where do you find the instruction to pretension the diaphragm? The instructions for the upright pump are very specific in the factory manual but no mention for the late pump.

[Dick Weiss]

David,

The same assembly procedure would apply to neutralize the diaphragm before adding the 2nd body-1/2.
The result gives equal pumping action (in both directions)

As mentioned in the shop manual--Group F, page SF 32, assembly of the diaphragm must not be creased
(@ the holes) when attaching the outer body 1/2 during the 6-screw snugging.
If not done, you'll see the wrinkles due to the spring over-pulling the rod which distorts the diaphragm outa flat!

Dick

[Larry Coreth]

Guys don't forget that the early and late style work on different basis, i.e. early, pressure is determined by diaphragm stroke length while the late style is determined by the diaphragm spring force, hence the different assembly procedure. Study the cross section drawings of Pages E23 and SF 27 to understand better.

[Dick Weiss]

Larry,

The late Ken Daugherty and I knew that the late pump kit has 2-different springs, but he found that the pump was
exceeding the max. pressure of 3-PSI. I suggested to add another gasket (or 2) the lessen the pressure--and it worked.
Spring differences? One has slightly larger wire diameter and slightly shorter than the other wsmaller wire diameter and is
slightly longer. You could use the existing spring during a rebuild, but checking the output needs a low PSI-reading gauge.

Dick

Dick

[Larry Coreth]

Dick,
Do you mean to say that the kits have two different diaphragm springs, part #9 on Pg. SF 27 ? I hope you are not confusing the plunger spring part #10 as being a second diaphragm spring ! The picture of the late style rebuild kit from Stoddard shows two springs, one is for the diaphragm the larger dia. and longer one and the plunger spring , shorter and smaller in dia.

I have not rebuilt a late type fuel pump lately nor actually measured the spring rate and compressed spring force of the diaphragm spring, I just measure the fuel pressure after assembly.

[David Grubbs]

Thank you all. The old diaphram (left in the photo) had the stiffness of a used sandwich bag. I reassembled as suugested with the new one (right). It takes some force but I can operate it pushing hard with a small stick on the rocker face. It seems to work fine.

Unfortunately the refurbished pump didn't cure my "missing and backfiring under load." But that's a different topic.

The old diaphragm incidentally developed circular bulges on both sides. Stretched out from fifty years of use? Both are actually three layers of rubber sheet.

[Larry Coreth]

David,
The new diaphragm will certainly conform ti the inside of the two halves !

Your problems under load sound all to much like a lean mixture. I would have checked main and air correction jets and/or float level first !

[Dick Weiss]

No Larry,

I meant the early fuel pump kit.

Dick

[David Grubbs]

Thank you Larry. I did replace a float a couple months ago. Level was OK. And I cleaned the jets. I'll check again. It idles OK and winds up without stumble if I hand throttle at the carbs.

It has 20 year-old Dellortos. It always idled high, and could be restored to running reasonably well if I tinkered with timing and points.

[Albert Tiedemann]

David,

...
The rebuild consists of applying some pressure on the rocker arm to pull down the diaphragm enough to contact the face of the lower body before adding the top 1/2 w/the 6-screws and snugging it together.
...
Dick

Use of VW328b [sets the diaphragm at the neutral plane] avoids the assembly problem and eliminates the dexterity implied for the mechanically challenged. I make copies of the Factory tool mentioned. Inquire offline.