Early XPAG oil pump priming

Not all XPAG oil pumps seem to be effective at self-priming which can result in anxious moments waiting for some oil pressure to build up when first starting an engine after an oil change.

One possible cause could be the inclusion of an anti-drain back flap valve in the modern spin-on filters that are used in one type of oil filter conversion. The oil pump already struggles to draw up cold thick oil from the sump against any sort of back pressure and the flap valve adds to the difficulty.

To help overcome any self-priming problems due to back pressure, the following guidelines might help.

1, Remove spark plugs so engine can turn freely using the starter motor, without loading the crank shaft bearings.

2, Fill up the new oil canister with fresh oil; this won’t help overcome the back pressure but will reduce the time for the oil pressure to build up when the oil pump is primed.

3, Unscrew the brass plug directly above the oil pump, and to the side of the lower dynamo bracket, the hex head needs a thin wall 1/4 BSF ring spanner.

4, Spin the engine using the starter motor until a cupful of oil and air bubbles have leaked out from the oil gallery via the opening. If after about 8 seconds no oil has leaked out, go to step 5. If oil does flow out, then replace the plug and spin the engine again. If, however, oil pressure doesn’t build up, remove the plug again and go to step 5.

5, This step attempts to remove all back pressures on the pump by partially disconnecting the pipe between the pump and filter. Unscrew the banjo bolt on top of the oil filter, making sure that the banjo adaptor doesn’t twist, as this puts a strain on the copper pipe where it enters the banjo adaptor. An adjustable spanner locked onto the adaptor could be used to stop it twisting. After unscrewing the banjo bolt until it is loose, spin the engine until oil squirts out. Retighten the banjo bolt and spin the engine until oil leaks out of the brass plug opening. Replace the brass plug and spin the engine until some oil pressure is indicated. Repeat 5 if needed.

6, Replace the spark plugs and check oil pressure with engine running. 7, As the starter motor can be made to run independently of the ignition, you may wish to consider spinning the engine on the starter motor for a few seconds before turning on the ignition. This helps circulate oil before the engine “fires up”, particularly after a long engine rest period…

…………Oil filter conversions.

Some rogue cast aluminium adaptors for spin-on oil filters conversions were made many years ago. They were not cross drilled, resulting in the pumped oil entering the filter element through its central core. The filter element’s convoluted membrane is not robust if oil flows in the wrong direction, but more significantly any anti drain-back flap valve would block oil flow. Oil would continue to reach the bearings by way of the oil pump’s by-pass valve; however, the oil would be unfiltered and at a lower pressure.

Here is a photo of a rogue oil filter adaptor and the opened-up oil filter showing the flap valve which would cover the holes in the flange.

Take care choosing oil filters, filters for modern cars running on much thinner oils may not be suitable for the 20W50 oils used for XPAGs. The most common spin-on filter conversion is intended for 76mm dia. filters with a 3/4 inch x 16 UNC thread form. Some filters have an inbuilt by-pass valve and these can operate with differential pressures as low as 7 psi. A coiled spring feature at the base of the central core is probably the by-pass valve.The GFE 443 and its equivalents are intended for A series engines and seem to be a popular choice.

Eric Worpe

Ed’s note: Eric says that it’s almost impossible to find the specifications of oil filters in terms of maximum flow rate at a particular oil viscosity, capture efficiency of a particular particle size, by-pass pressure operation if valve is fitted, anti-drain back flap-valve if fitted, oil pressure drop as function of flow rate and viscosity, dia. of sealing ring and thread form. Whilst he suspects that the GFE443, intended for ‘A’ series engines running on 20W50 oil may be ok, he is unable to endorse it.

As we are discussing oil filters, I have two of type GFE102. The label reads as follows:

Oil Filter Element
with ‘O’ Ring [on oil pump]

Free, but postage of £4.00 for sending the two would be appreciated.
jj(at)ttypes.org [Please substitute @ for (at)].