The 1.9 and 2.1 liter water-boxer engines were outfitted with the exact same oil pump as all VW Bug engines going back to around 1960. The gears in these pumps are only 26 mm wide. The main and rod bearing spacing on the crankshaft is identical to the Beetle engine, and the rod bearings used are actually the exact same part number as used in all Beetle engines since 1966. So why is it that 1986 and newer Vanagons seem to have oil pressure issues that the earlier 1983-85 Vanagons and Beetle engines did not? The answer is this: They all had very low oil pressure, but nobody knew it until VW installed a more elaborate dynamic oil pressure warning system with the introduction of the 2.1 liter engine in 1986. Is it really anything to worry about?
As you can imagine, we have disassembled thousands of water-boxer engines. We simply do not see low oil pressure- or lubrication-related failures, even though we know low oil pressure is common with these engines. It just doesn't seem to lead to any real issues. Replacing the original 26 mm pump with one of our larger 30 mm oil pumps (with machined cover) is cheap insurance, and it tends to make the low oil pressure warning buzzer shut up! That is what we install on all GoWesty rebuilt engines, including ones destined for the earlier 1983-85 vehicles without the warning buzzer.