It is best to avoid disturbing the oil pump, and unless it has to be removed for the renewal of worn or damaged parts it should be left in place. Should it require attention, however, or if it is necessary to clean out the oil passages in the crankcase it may be removed as follows :-
Remove the four fixing screws. DO NOT ATTEMPT TO REMOVE THE PUMP WITHOUT HEATING THE CRANKCASE. Heat the crankcase carefully over a gas ring to about 100 degrees Centigrade to expand the housing from the pump body, then holding the crankcase between several thicknesses of rag to protect the hands, raise it and bring it down smartly (timing case downwards) on to the flat top of the bench or other wood surface to jarr the pump cover and body out of place.
Having removed the pump, note that a brass shim K110 is fitted in the pump housing behind the pump body. Examine this, and should it show signs of wear obtain a new one. The pump spindle and gears may now be taken out for inspection. The gears must be a close fit in the pump body, and must turn quite freely without end float.
Should new gears be fitted it may be fouhd necessary carefully to lap these in, for which the following easily made equipment will be needed.
To maintain the pump cover truly concentric with the body, a split bush accurately turned to fit closely over the pump and cover and capable of being contacted on to them is required. Also a steel plate about ¼-in. thick and surface ground flat one side should be drilled, using the pump body as a guide, and tapped to take the four pump screws. The pump is then assembled and clamped in the split bush and secured to the steel plate with the four fixing screws. The ground flat face must be towards the pump body.
The lapping is done by rotating the pump spindle and running through the pump a mixture of Turkey stone powder and oil. In no circumstances must emery powder or valve grinding compound be used.
After lapping remove the pump from the plate and take it apart to clean away all abrasive matter. Refit the gears with clean oil and the pump is ready for re-fitting to the crankcase.
It should be noted that should the pump gears have locked due to foreign matter getting into the return side after being drawn up from the sump, a condition which may arise only in an early type engine without a suction filter, very great care is necessary to see that absolutely every trace of foreign matter is removed before re-assembly of the pump. Therefore in any instance when the pump spindle has sheared always make sure beyond possibility of doubt that the oil pipe which is cast into the timing half of the case and leads from the rear corner to the pump housing, is absolutely free from further pieces which might be drawn through to the pump and cause a repetition of the former trouble. In such cases, it is also essential to clean all external oil pipes and hoses and wash out the oil tank, subsequently re-filling with clean fresh oil.
In the event of it ever being necessary to extract the oil pump without the engine being dismantled, the following method may be adopted :-
Obtain a piece of flat mild steel approximately 4½-in. long by ½-in, wide by ¼-in. thick. Mark off the approximate centre and equi-distant from the centre drill two ¼-in. clearance holes 1 3/8-in. between centres. Also obtain two ¼-in. diameter studs approximately 1½-in. long, threaded at both ends with ¼-in. x 26 threads. From one end the thread should run down about 1-in., and from the other end about ¼-in. Two ¼-in. x 26 thread nuts will also be required. Carefully remove the oil pump cover after taking out the four fixing screws, and then tap out for about three threads two opposite holes in the pump body to receive the ¼-in. studs. Fix the studs in position. If the drilled steel strip is then placed across the face of the bevel box and over the studs and the nuts are then run down on the studs, it will be possible to withdraw the pump when the crankcase has been sufficiently heated by tightening down each nut a little at a time so as to draw the pump out of the housing.