No major modifications have been made, but the check valve and cylinder feed referred to on Page 34 have been deleted. The new check valve is more accessible and is carried below the oil tank.

The working faces of the cams are no longer drilled to provide an oil feed to the cams, and followers and the opening from the oil passage in the timing cover leads only to the cam wheel bush by means of the drilled cam spindle. An extra opening slightly above permits a supply of oil to be fed to the cam oil jet, the outer end of which locates in the cover. Oil from this is directed against the faces of the cams. Engines having this system can be identified by the later type smooth rounded timing cover.

An addition to the system is a fabric filter carried in a cylindrical chamber in the oil tank.

The Check Valve.

The check valve body carrying the 1-in. diameter check valve ball and the spring is screwed on to the strainer gauze assembly in the bottom of the oil tank, and the oil feed pipe union nut screws on to its lower end.

To remove the check valve it is necessary first to drain the oil tank. Next unscrew the oil feed pipe union nut and disconnect the pipe. Un­screw the strainer gauze assembly from the tank.

To take the check valve apart for cleaning hold the check valve body in the vice between aluminium or copper " clamps " to avoid damage to the hexagon, and unscrew the strainer assembly from it, disclosing the ball and spring. The ball, spring and seating may be cleaned and examined.

Should the spring be removed be most careful that it is replaced correctly, so that when the whole check valve is fitted to the machine the ball is above the spring. Cases have been reported where, due to incorrect reassembly, the ball has been placed in the check valve body with the spring above it ,thus completely cutting off the supply of oil to the engine.

After refitting the check valve make certain that the oil feed pipe is full of oil, so that the oil pump is primed, and if the pipe has been removed or the oil in it has run out, pour oil into the open end until the pipe is full and connect it at once to the check valve body.

Refit the tank drain plug, and refill the tank. Start the engine and check the return. If no return is obtained after a few moments running take off the oil pipe once more and prime the pump again. Refer also to next section.

The Fabric Oil Filter.

The fabric element needs no attention, but should be discarded and replaced by a new one after every 10,000 miles service. The element is carried in a cylindrical chamber of the oil tank and all oil returned from the engine has to pass through it before going back into the tank.

To remove the element it is unnecessary to drain the tank, but as it is always advisable when fitting a new element to start with clean oil we recommend not only draining the tank but removing it entirely and washing it out thoroughly in clean petrol and allowing it to dry off before refitting.

In order to remove the filter element the return hose must be disconnected from the union nipple below the tank.    (This will be disconnected in any case if the tank is being taken off).

Loosen the nut at the top end of the filter centre stud—in the centre of the filter top cap on the tank top and with a metal pan or dish held below the bottom filter cap prise the bottom cap away from the tank to allow the half-pint or so of oil trapped in the filter chamber to drain away.

The complete removal of the nut and top cap will allow the bottom cap with centre stud to be pulled out. Retain the joint washers used between the two caps and the tank.    The filter element may now be pulled out.

Wash out the tank as described above.

When dry fit the new filter element and replace the joint washer and the bottom caps, passing the centre stud up through the filter chamber.

Have the top cap with joint washer and nut handy for refitting. Hold the bottom cap and oil union firmly against the tank to prevent leakage and pour clean oil of the correct grade into the oil filter chamber from the top. When up to the level of the short pipe leading into the tank put back the top joint washer, the cap and the nut and tighten this securely. Hold the tank upright and refit to the machine. Refit the drain plug, see that the check valve is in place and refill the tank.

Connect up the oil pipes, being careful to see that the feed pipe is full of oil (see preceding section).

The object of filling the filter chamber is two-fold.   Firstly, if it is not filled when the filter is replaced the level of oil in the main tank will be reduced soon after starting by the amount of oil required to fill the filter chamber to the level of the outlet pipe. Secondly, no return of oil would be visible entering the tank after the engine was started until the chamber had filled.

Changing The Engine Oil.

Removal of the oil tank drain plug does not drain the fabric filter chamber, in which about a half-pint of oil will be trapped. To prevent this amount of used oil contaminating clean oil put in to the tank when draining and refilling we recommend draining the filter chamber also.

This is explained in the preceding section.