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Home-made fuel pump rebuilding jig
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DarrylD
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PostPosted: Thu Mar 24, 2005 10:19 pm    Post subject: Home-made fuel pump rebuilding jig Reply with quote

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.

Image may have been reduced in size. Click image to view fullscreen.


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!


Last edited by DarrylD on Sun Mar 01, 2009 7:32 pm; edited 1 time in total
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sovereignsamba
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PostPosted: Fri Mar 25, 2005 12:28 am    Post subject: Reply with quote

thats awsome!
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schristen
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PostPosted: Wed Aug 03, 2005 3:00 pm    Post subject: preload pump Reply with quote

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.
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bill may
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PostPosted: Wed Aug 03, 2005 8:26 pm    Post subject: Reply with quote

it will last longer if rebuilt per manual(real bentley or offical workshop manual from vw)
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Gary
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PostPosted: Fri Aug 05, 2005 5:51 pm    Post subject: Re: preload pump Reply with quote

schristen wrote:
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.


There's a method to the madness in those old manuals. I think the engineers had a bit of an idea of what they were doing.
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dirtylawnchair
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PostPosted: Fri Aug 05, 2005 6:48 pm    Post subject: Reply with quote

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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LHG
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PostPosted: Thu Mar 08, 2007 10:39 pm    Post subject: Reply with quote

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
Image may have been reduced in size. Click image to view fullscreen.


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.
Image may have been reduced in size. Click image to view fullscreen.

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mtb7001
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PostPosted: Sat Feb 14, 2009 10:43 am    Post subject: Reply with quote

hey all, the original pic of the wood tool expired last fall, could someone please repost it? thanks
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mtb7001
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PostPosted: Sat Feb 14, 2009 11:13 am    Post subject: Reply with quote

thanks for the PM : )
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babarogue
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PostPosted: Fri Oct 08, 2010 2:20 am    Post subject: Reply with quote

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) Cool
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35mastr
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PostPosted: Tue Jan 04, 2011 12:54 pm    Post subject: Reply with quote

Very informitive thread. Nice to these little tricks when rebuilding parts that actually need a preload for them.
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61SNRF
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PostPosted: Tue Jan 04, 2011 6:58 pm    Post subject: Reply with quote

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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herbie1200
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PostPosted: Mon Jan 10, 2011 4:26 am    Post subject: Reply with quote

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?

Last edited by herbie1200 on Mon Mar 07, 2011 3:58 am; edited 1 time in total
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Harris
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PostPosted: Mon Jan 10, 2011 6:59 am    Post subject: Home Made Fuel Pump Tool Reply with quote

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.

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SurfsUP
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PostPosted: Sun Mar 06, 2011 10:24 pm    Post subject: Reply with quote

herbie1200 wrote:
I have to rebuilt 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?


I'm in the process of rebuilding mine and was wondering the same thing of just bolting the fuel pump up to the engine and turning the engine.

Will this work?
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Harris
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PostPosted: Mon Mar 07, 2011 6:41 am    Post subject: Home Made Fuel Pump Reply with quote

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.
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EA812
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PostPosted: Tue Mar 08, 2011 3:06 pm    Post subject: Reply with quote

Love the home made tools!
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SurfsUP
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PostPosted: Wed Mar 09, 2011 10:52 am    Post subject: Reply with quote

Thanks Harris for the info!
I wanted to do it on my engine cause I'm too lazy to build one of these. Very Happy
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
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Harris
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PostPosted: Wed Mar 09, 2011 10:59 am    Post subject: Home Made Fuel Pump Reply with quote

David,

Quote:
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


I'm guessing, but I don't think the 14mm measurement is the same for the 36. I have no experience with the earlier pumps. Someone here will know.

Harris
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Bart Dunn
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PostPosted: Wed Mar 09, 2011 11:32 am    Post subject: Re: Home Made Fuel Pump Reply with quote

Harris wrote:
David,

Quote:
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


I'm guessing, but I don't think the 14mm measurement is the same for the 36. I have no experience with the earlier pumps. Someone here will know.

Harris


36hp is longer--I want to say it's 35mm. It's on here somewhere, and perhaps even in the Bentley manual(s).
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