The pressure Release Valve is adjustable and controls the working pressure when the engine is running. Excess pressure is released past the valve and returns direct to the sump through the open oil union shown alongside pipe ‘I ' in Fig. 20.

The valve consists of a spring loaded ball-ended plunger carried in the body ' B '. The pressure of the spring on the plunger is controlled by the setting of the adjuster C '. The body is secured to the outside of the crankcase by two oil unions that are screwed into it from inside the case through the side wall. Gaskets are fitted between the body and the outside of the case, and between the heads of the unions and the inside of the case. In the ordinary way it should not be necessary to detach the body, but is advisable, if the engine is dismantled, to take the opportunity to check the tightness of the unions and to tighten them if required.

Refitting the Oil Pipes.

The arrangement of them is clearly shown (Fig. 20). Screw the unions into the crankcase and flywheel housing respectively. Tighten them gradually and turn the crank meanwhile to make certain that they do not cause the shafts to bind in the bushes. At the slightest sign of stiffness remove the offending union and file a little off the inner end. They must screw in firmly without touching the mainshaft bushes.

Hold the distributor block assembly opposite the hole in the crank case, fit a gasket over the union, and thread the latter through the hole. Fit a second gasket over the threaded end protruding inside, and screw the union into the distributor. Do not tighten it for the present.

Connect up the reduction gear pipe 'K' to the centre outlet of the distributor, and the pipes 'A', 'I', and `J' as shown tightening their union nuts securely. Finally hold the hexagon of the distributor block pipe firm with a spanner, and screw the union firmly in until tight. Offer up the oil sump to check that it does not foul any of the pipes. Reset any that require moving, and tighten the unions again.

Prime the pipes by forcing clean engine oil in through the distributor block pipe. The oil sump can now be refitted.

The sump fits with the drain plug boss facing the rear. Fit a new gasket and follow it with the sump. Make sure that the internal oil pipes clear it. See previous sections. Put back the four pressure straps, the lock-washers, and nuts. Tighten evenly. Fit the drain plug and gasket and tighten securely.