First remove the Carburetter, Exhaust Pipe, Sparking Plug, and Oil Return and Drain Pipes from the Rockerbox and the Exhaust Valve Lifter Cable. Drain out the Oil from the Bevel Gear casings and Vertical Shaft cover by removing the Plug at the base of the Timing Gearbox. Loosen the two Gland Nuts K52, slip the lower Gland Nut up the Tubular Cover K50, and spring the small Jump Ring out of the groove to triable the part K50 to be pushed down into the bottom Bevel Gear Bush. This will expose the Coupling Joint K35.
Now turn the engine round until points on the Contact Breaker are just breaking, and at the same time the lower portion of the top joint in the vertical shaft is facing exactly in line with the Crankshaft. The piston should now be at the top of its stroke. Should this position not be arrived at at once, revolve the engine a number of times when it will be found that the relative position of the piston and joint will be constantly changing until the desired positions are attained. Now mark the teeth of the large bevel wheel K18 and pinion K19 through the inspection plug hole K99 so that they can be readily replaced when reassembling. An indelible pencil is useful for this purpose. Next loosen right out the four bolts holding the Rocker Box casing which can now be withdrawn together with the bolts. If there is difficulty in getting the Rocker Box past the Valve Springs, it can be easily overcome by turning the Valve Spring until a space in the Coils comes opposite the small projecting lugs on the Rockerbox. Now remove the four Cylinder Head Bolts, when the Head can be lifted off. If you do not possess a tool for removing the Valve Washers and Cotters, it is advisable to obtain a Terry o.h.v. spring remover. The 250 c.c. size is the most suitable for single port Engines. We supply and recommend this tool Part No. KA163 a 500c.c. type Part No. KA163/3 is necessary for double port engines.
To grind valves, use very fine emery powder mixed with oil or paraffin. Only a very small quantity should be used. The Valves must be revolved backwards and forwards and frequently lifted up and dropped down again in a different place each time to ensure smooth seating. To revolve the Valve a small tool is necessary. We supply a grinding tool Part No. KA164 at 1/2 post free.
Should the valves be very badly pitted, we can reface them for a small charge. After refacing, it is advisable to grind them into the seating of the Cylinder Head as previously explained.
To replace the Valves and Valve cotters without proper Tools is not easy. A piece of wood can be inserted inside the head to hold the valve in position, and a vice used to compress the Valve Springs and Washers while the small split Collars are inserted. This is much easier done by using a special tool which can be obtained from us.
To take off the Cylinder the four nuts at the base will have to be removed To detach piston from the connecting rod it is first necessary to remove the circlip from the boss of the piston. This is a small spring steel ring and is removed by taking a sharp pointed instrument and prising the ring out of its groove. A small slot is provided in the one piston boss to facilitate this operation. The gudgeon pin can then be pushed out from the opposite side of the piston. Before proceeding to remove circlip it is advisable to cover the opening in the top of the crankcase with a rag to prevent the circlip dropping into the crankcase.