Home-made fuel pump rebuilding jig

[Frodge]

[tasb]

He probably used the wrong jig. There are at least two different specifications. The 36 hp jig is quite different than the 1300+. There ws something very wrong if he had no diaphragm seal showing between the two sealing halves.
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Roads Scholar &
1957 Kombi low mileage 36 hp governor equipped M 178 Slow Drag Winner 2014, 2015, 2018

1965 hardtop Deluxe Microbus owned since 1990 M 620 factory 12 v 1500cc

1961 (October)Single Cab- Road Trip Workhorse

[kreemoweet]

[easy e]

I bought some rebuild kits from Europe... hoping they were better than Brazilian.
Who knows... they may be Brazilian.

At any rate... I wanted to know more about what I bought & how it stacked up to original.

I picked out six APG pumps... a few round top & a few square top... just to mix it up.

All six of the pumps still had APG diaphragms.

Using Hooke's law (F=kx)... I figured the biggest thing to look at first was the spring.

I measured the spring free length.

Then I wanted to know how much force it takes to compress the spring a certain distance... since the spring applies a resisting force at a constant rate.

I put the diaphragm and calipers on the scale & zeroed it out.

Then I got a socket that fit over the pin & compressed it.
Took a reading off the scale and at the same time... held the calipers in the same fashion as when I measured the free length (not pushing down with the calipers).

It was tough to read two things at once... so I gave up on trying to do that.
I decided to just push the socket down... and put the caliper on it and ignore adjusting the caliper & read it later... just focusing on the scale reading and if the caliper was touching where it should. Looked for the reading where the caliper was just on the cusp of bobbing off the diaphragm.

Turns out... the new kit diaphragm pin is a fuzz over a 1/16"shorter than the original... and the spring stiffness is quite a bit stiffer

Using the old spring (as previously discussed) is the way to go.
It was time for dinner... so didn't delve into diaphragm stiffness differences... probably negligible (compared to the spring).

The actuating foot in the rebuild kit seems effectively the same as original.
When the pivoting axes are aligned... each end seems in basically the same place.

Here's a pic of the old & new diaphragms side by side.

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aka: Evan
Spreadsheet for Bus RPM, based on gearing & tire size (Excel format)
Searchable, click-navigable 1958 Bus Parts List

[wcfvw69]

I'd be interested if you measured the pin length between the original and new one like in these photo's of the POS Wolfsburg West kit?
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[easy e]

Springs removed for accurate measurement.

New = 33.13mm = 1.304"
Original= 35.25mm = 1.3875"

A difference of = 2.12mm or 0.0835" (just under 3/32")
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aka: Evan
Spreadsheet for Bus RPM, based on gearing & tire size (Excel format)
Searchable, click-navigable 1958 Bus Parts List

[kreemoweet]

[wcfvw69]

[easy e]

The effective pin length is from pin tip to the upper surface of the upper diaphragm plate.
Ya, I was lazy & playing horseshoes... because the source of significant error is in the force measurement (freehanding the scale).

Please feel free to improve on the results, approach... I encourage you.

The free length is a fuzz below where I measured... the top of retaining disc.
But, it's lost in the noise because of the scale accuracy thing.

Consistency in approach provides the qualitative aspect ("the take away"), so please don't take jabs at the decimal place & number of significant digits.

Repeat the process to your desired level of accuracy & the spring rate ratio will be virtually identical. I numbered the diaphragms, per column 1. I'd be happy to mail them to you, if you'd like to give us a similar presentation & provide the spring rate ratio to compare to mine.
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aka: Evan
Spreadsheet for Bus RPM, based on gearing & tire size (Excel format)
Searchable, click-navigable 1958 Bus Parts List

[easy e]

Thanks for the kind words Bill.
I don't mind being challenged in the slightest.
I get challenged everyday & do the same.
The truth always comes out.
I've extended my offer for him to accept, or not.
_________________
aka: Evan
Spreadsheet for Bus RPM, based on gearing & tire size (Excel format)
Searchable, click-navigable 1958 Bus Parts List

[piperj]

easy e:I ran into these same issues a couple years back when I rebuilt my stock pump with WW kit. I ended up leaving the pump with the new kit installed on the pretensioning jig for a few days and it did stretch a bit; enough to get the top assembled with enough of the diaphragm showing around the edge and not leak. It seems we need to get kits that really work; let us know if you find a worth while source or amended tensioning technique. This is a good thread to keep updated.
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67 Sun Roof Bug

[Silvester]

Some great stuff here. Tagging it for future reference. New to air-cooled, trying to find a good rebuild kit for my Early 61 40HP.
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Jeremy

Vw's currently caretaking
61 Beetle - Pastel blue
79 Scirocco - Kolibri Green
80 Scirocco S - Alpine white - Drake built 1.8 W/ Stage II Callaway.

[Who.Me?]

Does this look right for the diaphragm with 14mm preload?...

I've been rebuilding this for the 1600 dual port engine in my Splitty Single Cab.
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Andy


Looking for info on my truck's history. Are you from Campbell California or nearby. Do you recognise it? ... http://www.thesamba.com/vw/forum/viewtopic.php?t=636786

[wcfvw69]

[heimlich]

Very nice work on that detailed drawing.

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[wcfvw69]

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[wcfvw69]

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