Home-made fuel pump rebuilding jig

[DarrylD]

You're rebuilding your fuel pump and so you break-out the big-blue phonebook-sized factory workshop manual. At one point in the procedure it says, "Insert fuel pump gauge VW-328D to depress rocker arm and pre-load diaphram."

I don't have special tool Gauge VW-328D but figured I could make one to depress the fuel pump rocker arm exactly 14mm as required by using a fuel pump gasket as a template for the location of the "pump rod" and drill some holes in a block of wood for 5/16" diameter bolts. The center bolt serving as the "pump rod" was positioned at 14mm exposed and drilled in from the side and pinned in place with a nail.

Once I got the diaphram installed in the bottom half of the fuel pump, I bolted it onto the the wood block with nuts on the two outer bolts. Tightening the flange down to the wood allowed the center bolt to depress the fuel pump rocker arm 14mm, the diaphram went down the right amount and I screwed the top half of the fuel pump in place.

The important thing is that I had two hands available to stretch and hold the diaphram smooth as I positioned the top half of the pump and inserted the screws.

The rebuilt fuel pump worked perfectly first try!

[sovereignsamba]

thats awsome!

[schristen]

I rebuilt my first pump last night and didn't even think to look at the shop manual... why would I need to preload my diaphram? Since it's all flexible and open to the outside air, I don't see the advantage of the preload, unless it just helps align the diaphram to put in the bolts.

[bill may]

it will last longer if rebuilt per manual(real bentley or offical workshop manual from vw)
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[Gary]

[dirtylawnchair]

If you dont preload, it will rip faster and you will start getting gas in your oil.

I made a set up in a "soft jaw" of a vise for my 36hp pump to preload. Good work!
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Paulie
63 Standard OG paint

[LHG]

I am in the process of rebuilding my pump and taking a good look at the preload issue. Here is what it appears the preloading does, all of which makes it a good idea, but not mandatory.

1. Centers the metal diaphragm in the pump.
2. Makes the rubber stress/stretch equal around the diaphragm.
3. Makes reassembly MUCH easier.

It seems VW made a special tool for lots of jobs and the fuel pump is no different. I used a wood mock-up like the above photo and it worked fine.
Without preload

With preloaded. Even thought the rubber diaphragm is flipped up a bit. This will be very easy to line up and assemble.
You can also see I used a screw to hold the preload bolt in place.

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Brian O'Kelly
Central Coast Chapter, CA - Vintage Volkswagen Club of America
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[mtb7001]

hey all, the original pic of the wood tool expired last fall, could someone please repost it? thanks

[mtb7001]

thanks for the PM : )

[babarogue]

Hello all,
I gues I also have something useful on the diaphragm preload topic:

The premature wear of the diaphragm is one problem when preload is not done. The other also serious problem could be wrong fuel pressure that the pump will deliver to the carb. The link below is a practical experience on that:

http://www.thesamba.com/vw/forum/viewtopic.php?t=1...bda5618695

Higher fuel pump pressure will keep the inlet valve in the carb more open than it should be, so the level of fuel in the bowl will rise. This will affect the work of the carburettor and therefore the fuel economy (high rpm, lower mpg), fuel mixture composition, exhaust composition, CO emission etc. Also, a rich running carburettor over the time can have other, mostly unfavorable effects on the engine and we don't want that.

P.S.
Sorry to post this late, but I also have a fuel pump problems currently, for the first time after almost 37 years of service (easy to guess, it's the diaphragm)
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[35mastr]

Very informitive thread. Nice to these little tricks when rebuilding parts that actually need a preload for them.

[61SNRF]

It's a good idea to preload any rubber diaphram when assembling. The same goes for the accelerator pump and choke pull off diaphrams in the carburetor, but you only need your finger to do those. Putting the rubber in the center of it's operating range ensures that it's in a relaxed position when the cover is tightened.
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-Bruce

An ounce of prevention is worth a pound of cure.

[herbie1200]

I have to rebuild my pump. So I ask: why not to fix the lower part of the pump on the engine, rotating the pulley until the elevation is exactly 14mm? Is it a good idea?

[Harris]

I made one a while back after seeing DarrylD nice reproduction. They do the job with no guess work. Easy to do. I used an old screwdriver shank for the adjustment rod.

[SurfsUP]

[Harris]

SurfsUP,

I don't see why you can't do it on the engine as long as you like your measurement of 14mm on the pushrod. They will run without any preloading (don't last as long I think), but you probably will have a problem in getting the correct fuel pressure by having to add numerous gaskets. The jig is easier for me to assemble the pump at the workbench and after install I usually need to add just one gasket. If you build a spare pump later then the the jig is most handy.

One added thing. When you preload the diaghram the screw holes in the diaghram will be a little off with the base. I had to turn the dighram some to line them up. When putting the top on you will need to gently work the screws in to keep from ripping the holes in the diagram. Point is this so much easier working at the work bench than on the engine.

[EA812]

Love the home made tools!
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[SurfsUP]

Thanks Harris for the info!
I wanted to do it on my engine cause I'm too lazy to build one of these.
I just picked up a 54-55 36hp complete motor from my friend and it's going in my 56 oval. My friend said it was running when he took it out of his friend's oval and it's been sitting for a few years. The 36hp is in really good condition and I am in the process of cleaning it and resealing it with a new gasket kit. I wanted to rebuid it but I've never done it.

The fuel pump looks like it from a later 36hp, it has a brass bolt on the top that unscrews and there is a plastic filter inside. Is the 14mm measurement the same for all fuel pumps? I can turn my motor and I can see the metal pushrod move in and out. So, from what I understand is that if I can turn motor until the pushrod is 14mm then I can just bolt the fuel pump on and install the top portion of the pump. Am I correct?

Thanks,
David

[Harris]

David,

[Bart Dunn]