THE AUSTIN SEVEN OIL PUMP

A popular misconception is that the standard Austin Seven oil pump is an inferior piece of engineering design and, therefore, unsuitable for fitting to any engine other than the splash lubricated (spit and hope) standard type.

The opposite is the case as the Austin pump is a superior design and quite capable of outperforming all but one of the pumps currently considered as better alternatives.

The origins of this misconception almost certainly lie in the failure to appreciate that the Austin oil pump was originally selectively assembled, giving the lie to the often held belief in the complete interchangeability of all Austin Seven parts and that “modification” has to be carried out in a most carefully defined manner if the pump is to operate successfully.

It is easy to refute the pump’s current reputation on the results of our measurements of volume, pressure and it’s total reliability in use.  A correctly assembled pump will deliver oil, of the correct SAE 40 type for which it was designed, at a rate of approximately 0.6 litres/1000 RPM/minute.  This equates to a delivery rate of over 5 pints of oil a minute at an engine speed of 5000 RPM.  What is more this oil will be delivered at a pressure of over 140 psi if no relief valve is fitted.  These figures can be exceeded if the pump has been modified correctly.  These figures are the result of observation over more than 100,000 km of extreme use in all conditions from -25°C to +40°C.  As for reliability; during this time no problems or failure have ever been experienced.

 Examining the pump in more detail it consists of a pair of spring loaded steel vanes carried in a slot in the steel spindle which is eccentric in the brass pump body.  This assembly is retained in the housing by a base plate which also incorporates the oil pick-up from the sump.  The oil is fed into the pump chamber from a vertical gallery via two holes in the chamber wall.  There are two similar holes through which the pressurized oil is delivered to the main crankcase oil gallery.  The whole affair is driven by a gear on the rear end of the camshaft which mates with the gear on the top of the pump spindle.   This is fitted on a taper with a keyway and is attached by a nut and spring washer.  

From the above description it will be obvious that the following are of the utmost importance for the pump to operate at maximum efficiency:-

1).        The fit of the vanes in the spindle.

2).        The fit of the spindle in the brass pump body.

3).        The fit of the drive gear.

4).        The pre-load on the vane springs.

5).        The position of the inlet and outlet holes in the pump body.

To achieve an ideal situation it is important that the pump assembly meets the following criteria:-

a).        The inlet and outlet holes in the pump chamber are of equal size and are aligned as vertically as possible.

b).        The pre-load of the vane springs is maintained with no damaged or distorted springs.  If the pump body has been bored out new springs must be fitted that allow for this oversize and maintain the correct pre-load (using the original springs will not do).

c).        The vanes should be a good sliding fit in the spindle with the chamfered ends at the top.  They must also be shorter by not more than 0.001 inches than the slot in the spindle and both vanes must have the same dimensions (a matched pair).

d).        The spindle, which is set eccentrically in the pump body, should have a clearance of no more than 0.002 to 0.003 inches at its closest point to the chamber wall.  It is vital that this dimension is not exceeded if the pump body is bored out.

e).        In addition to the above the spindle should be no more than 0.001 shorter than the pump chamber so that there is clearance when the base plate is fitted.

f).         The paper gasket fits between the pump body and the crankcase and NOT between the pump body and the base plate.

g).        The drive gear should be a very good fit on the taper and key.  It is important to make certain that it sits concentrically on the shaft and has not “ridden up” on the key which is often damaged and may need replacement or careful cleaning up with a needle file.

h).        When using a pressure lubricated crankshaft, “Ulster” or “Phoenix”, the standard oil pressure relief valve spring must be replaced by a stronger one as the standard spring will allow the oil to “blow off” at around 35 psi.

i).         Check the oil pressure relief valve ball and if it has marks on it like a “tennis ball” replace it.

j).         Always use SAE 40 oil as this is what the pump was designed for.

An Austin Seven oil pump and pressure relief valve will be quite adequate for the splash feed lubrication of a standard engine. The oil pressure should be about 5 psi hot and if more check the oil jets by removing the plugs in the crankcase and clearing them with a piece of wire before replacing the caps.

For pressure lubricated engines using Castrol XXL mineral oil or Castrol R 40 vegetable based oil the pump will deliver more than enough volume and with a stronger pressure relief spring between 45 and 65 psi when hot.  Although higher operating oil pressure can be obtained this is not recommended as it is unnecessary and simply strains the pump, drive gears and twists the camshaft.

                                                                                                                        January 2007