Norton Commando Workshop Manual

## Engine/Primary Transmission

# C

### SECTION C6

### RESEATING THE VALVES

After renewal of valve guides (as in Section C5) or where the valve seats are in badly pitted condition it is necessary to recut the valve seats. During decarbonising or after recutting the valve seats the valves must be reground.
Cutting the valve scats - Valve seat cutters, a suitable arbor and pilot are available under the following Part Number: 063969
| Arbor and pilot. Valve seat cutter (45°). Blending cutter.
Before commencing to cut the seats we stress that the essence of cutting valve seats satisfactorily is to remove the minimum of metal and to use the cutters in such a way as to prevent possible "chatter" in the cutting pattern. Proceed as follows:
1 | Assemble the cutter and pilot the arbor.
2 | Enter the pilot into the valve guide from inside the combustion chamber hemisphere.
3 | Applying sufficient pressure on the arbor to give a clean cut without "chatter", take the first 120° cut.
4 | Repeat the operation, 120° at a time until the seats are cleaned up free of any pitting.
5 | Wash with gasoline (petrol) and blow clear any displaced material.
6 | Cut the other valve seats which are affected by pitting.

### SECTION C7

| Grinding-in the valves- Examine the valve heads for cleanliness and the valve stems for cleanliness, excessive wear or pronounced scuffing. Excessive wear or scuffing wouid necessitate renewal of a valve. If the valve head facings are pitted, they can be cleaned up on a valve facing machine though excessive removal of material is not recommended since it wouid affect the performance of the valve.

Grind the valve facings to the seats as follows:
7 | Use a good quality fine grade grinding compound and smear a little compound all round the valve facing.
8 | Drop the valve into position and using a backward and forwards rotary motion by holding either the valve head or valve stem with a suitable grinding tool, lap the valve facing to the seat.
9 | Lift the valve off the seat and rotate the head 180°.
10 | Repeat the lapping and rotating operations until there is a uniform dull grey bedding-in pattern on both surfaces.
11 | Wash the affected areas free of grinding compound, then assemble the valves and springs to the head as in Section C3.
12 | Test the seating of the valves by supporting the cylinder head with valves assembled, hemispheres upwards. Pour gasoline or kerosene (petrol or paraffin) into each inlet port and allow 20 seconds to elapse. If the liquid has not passed the seatings into the combustion chambers in this time, the lapping operation has been successful. Repeat the operation at the exhaust valves.

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