Remove the petrol tank after turning off both taps, disconnecting the petrol pipe and undoing the tank fixing bolts at the front and rear. Unscrew the ring holding the mixing chamber top to the carburetter, remove slides and take off the carburetter, undo the exhaust pipe clip at the cylinder head, take off the exhaust pipe and take out the sparking plug. Undo the bolts holding the rocker covers to the side of the rocker box and top cover. Undo the nuts holding the top flange of the push rod tube. Next undo the three bolts holding the rocker box to the cylinder head and loosen the gland nut on the push rod tube which will now be found to be finger tight. Lift off the rocker box complete. Undo the four cylinder head nuts and lift the head off the barrel. If it is necessary to remove the cylinder barrel this can then be lifted out of place after taking out the four long studs which screw into the nuts at the bottom. A copper cylinder head washer is fitted and this must not be lost - it should be hung up carefully to avoid damage.
To remove the valves obtain a Terry Valve Spring Remover, this is available from us price 8 /-, part number K.A. 163, which should be quoted when ordering.
To grind in the valves use very fine emery powder mixed with oil or paraffin, or one of the proprietary class of valve grinding compounds. Only a very small quantity should be used. The valves must be revolved backwards and forwards and lifted frequently from the seatings to prevent grinding concentric rings on the seatings. When the valve is lifted, it should be brought down in another position to ensure a good seating. To hold the valves when grinding we recommend the special tool which we can supply for this purpose, price 1 /2 post free. Part No. KA164 /2.
If, after prolonged service, the seats of the valves are pitted badly or are worn concave, the valves should be refaced in a lathe. This will avoid grinding the seats in the head unnecessarily. We will reface valves at 3 /-, per pair (return postage extra) if sent to these Works. Similarly, if the seats in the head are pocketed or require trueing up, we can recut them and remove superfluous metal from around them if the head is sent to us. The charge is 6/- return carriage extra. When sending the cylinder head, always pack it carefully in a wooden box, as the fins are brittle and break easily. Cardboard or paper only are useless as packing. When replacing the valves and springs, see that the valve cotters are properly fitted into the serration. They must not be mixed as they are machined in pairs. To remove the piston take out the circlip. This is a small spring steel ring and is removed by prising it out of position with a sharp bradawl or a suitably pointed instrument by means of a small slot which is cut in one of the piston bosses. The gudgeon pin can be then pushed or lightly driven out from the opposite side of the piston. If it is tight heat the piston which will ease the pin. Always use a soft metal punch for tapping out the gudgeon pin and always cover the cylinder opening in the crankcase with clean rag stuffed in to prevent the circlip or anything else accidentally dropping into the crankcase. Always note, before removing the piston, which side of the engine the slot for the removal of the circlip is fitted, or mark the piston so that it is put back in the same position.