FYI - I took apart the mitsubishi mid-80's pickup 10mm pump to do some learning about its internals and do some comparing with the 1.6lTD (from a 1984 Jetta) pump parts.
Although the camplates were constructed differently (the mitsubishi one seemed like a heavier piece), the displacement of the mitsubishi camplate is the same 2.2mm as I believe is on the 1.6 camplate. From the picture it seems that the mitsubishi camplate has a slightly softer profile than the VW (IE: slower movement of the pump head), but it's hard to be certain just from looking, as they are pretty close (1.6 vw on left, mitsubishi on right):
The two camplates also have as closely as I can tell, an identical recessed diameter for the "plunger foot". (Tested by crudely measuring, as well as test fitting the same plunger into each and observing equal amounts of "play".) The plunger drive pin in each is also a matching 3.5mm diameter. (1.6 vw on left, mitsubishi on right):
Takeaway: given the matching plunger foot diameter and similar camplate displacement, the 10mm mitsubishi plunger may be a suitable swap-in upgrade for a 1984 1.6TD VW pump (for either maintaining the original 1.6 VW camplate, or swapping the mitsubishi camplate along with the plunger.)
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Interestingly, the plunger return springs were not the same. Although nearly identical in free length, the mitsubishi springs obviously had thicker gauge of wire, and also had one extra coil (1.6 vw on left, mitsubishi on right):
Looking at both, I thought the VW one might be good for some more pre-loading and lift, if the wire material was strong enough. Well, it turns out that the wire material was not strong enough to remain undeformed after being coilbound. It actually deformed quite a bit. :shock: (in pic below, two vw 1.6 plunger springs are shown, the one on left hasn't been coilbound and the one at the right has)
Can the mitsubishi spring take being pre-loaded to coilbind? I'm guessing it can get closer given it has less travel to go and also some thicker (& probably stronger) wire, but I don't wish to test it on my only pair of these springs. I wouldn't mind testing and comparing the spring rate of these two different springs, if I can rig up such a test though.
How much pre-load the plunger return springs should be set up with, and deep the plunger should be set up, I am not certain. If anyone has any advice or VE technical service manual information covering this (any information on the topic - what methods are used to measure it and set it up, what the factory recommended settings are, etc), please let me know, as I would be very interested in it. I have a feeling that it's pretty important and is something that the trained/certified VE pump rebuilders check and set. I would really like to know what I'm doing and not blow up a pump if it could be avoided. Thanks!
It is likely that a plunger upgrade test of some sort will be in my future after I get my Rabbit autocrosser up and running and the fresh rings broken-in, and maybe the custom intake manifold fitted and tested.
