The oil pressure plunger, which is kept under tension by a spring, is hidden behind a rather large locking screw in the bottom of the crankcase. On engines up to 7/1969, there is only one plunger diagonally under the oil pump, after which there are two plunger, the second being on the flywheel side.
Volkswagen chose at the time to make it a slotted screw for which a very large screwdriver is required. Good tools account for half the work, and this certainly applies to the removal of this locking screw, but unfortunately, many people try it with a screwdriver that is too small, causing the slot to break.
This improved version has an Allen socket, so you don't have to search for a proper screwdriver. Using a 10mm Allen wrench, which everyone has in their toolbox, you can effortlessly turn the locking screw in and out of the crankcase.
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