In the left hand thread nut on the timing side mainshaft a ¼-in. dia. steel bearing ball is held into contact by a light spring with a seating cut inside the nut. The purpose of the ball valve is to prevent oil draining by gravity from tank to crankcase sump when the engine is stationary.

Should it be found that the exhaust smokes excessively on starting or should the engine be difficult to start due to an accumulation of oil in the sump the cause is possibly this valve failing to close properly. Sludge or dirt in the oil through keeping oil too long in circulation may be responsible.

To attend to the ball valve proceed as described on page 38.

Remove the left hand thread nut from the mainshaft. Take care not to drop and lose the ball while taking off the nut. The spring will probably remain protruding from the shaft and may be pulled out carefully. Examine the spring and if damaged or distorted obtain a new spring, catalogue number K.115. Clean out the oil holes in the nut and clean the seating. The seating may be lapped, using a spare ¼-in. dia. bearing ball soldered to a short piece of brass bar, or the ball may be reseated by tapping it against the seating using a short punch whilst supporting the nut, open end upwards (with the ball on the seating) on a flat solid metal surface, such as the back of a bench vice. It is inadvisable to use much force as this tends to widen the seating and so reduce the unit pressure upon it making subsequent leakage more likely. If in any doubt as to the condition of the ball valve seating fit a new nut, catalogue number K114 /2