Mounting the (Dreaded) BSA WDM 20 Oil Pump

The Army Manual states that "On no account remove the oil pump unless it is absolutely necessary", and that warning is not without ground. Removing it is no big deal, but getting the thing back in its place is another matter, especially when the engine is already in the frame.

Now, you think you HAVE to remove that pump for one reason or another, like to test the functioning of that small ball valve, the wear of the gears, or just plain curiosity. Then you'd better prepare the tools you will need; for instance a 1/8" WW socket, the outside turned down to 12.2 mm.

??? Those little bolts that hold the pump are 1/4" WW ? Yes, completely true, but due to the cramped space inside those 1/4"bolts have the smaller 1/8"WW head, and to fit the socket you have to slim down the outside (put a tungsten tool in your lathe tool holder, those sockets are sometimes REALLY hard, DAMHIK).

Following step: take two pieces of 6 mm rod, about 15 cm long (I used those huge 6"nails) and put 1/4"WW thread on one side of each; 10 mm will suffice. You can use 1/4" rod, but threading is easier on 6 mm, and the resulting sloppy fit in fact makes mounting the pump a bit easier.

Now do the following:

screw both rods in the opening in the crankcase,
slide the oil pump upwards over the rods until it touches its seat; it will fit only one way. Sometimes you should wiggle it a bit, or turn the pump spindle so it will engage the notch in the driving spindle.
unscrew one rod, while holding the pump with one finger against its seat, insert one of the 1/4"bolts finger-tight,
unscrew the second rod, replace it with the second 1/4" bolt, and tighten both bolts using the modified socket.

Satisfaction! You did it! Until you see on the workbench part number 65-2618: the gasket you forgot to put on top of the pump. DAMHIK again....

Hans Muller,
WDM20 58764

Version July 2007