Norton Commando Workshop Manual

## Engine/Primary Transmission

# C

### SECTION C12

### CYLINDER REBORING AND OVERSIZE PISTONS

After considerable mileages, or on engines where air filtering has been inefficient or oil changes neglected, wear may be expected on the cylinder bores or pistons. The maximum degree of wear may be expected to occur at the top front and rear areas of the cylinder bores. Similarly, the maximum wear will take place on the front and rear faces of the pistons. Measure the cylinder bore diameter front and rear within 1/2 in. (12.70 mm) of the top of each bore and again front and rear at a point in the bore below the piston ring swept area. If the bores are in acceptable condition, the difference between the measurements should not exceed 0.005 in. (.1270 mm).
An alternative (but less accurate) method of measurement is to place one compression ring in the bore, approximately 1/2 in. (12.70 mm) from the top and measure the ring gap with feeler gauges. Place the ring lower in the bore below the piston ring swept area and again measure the gap. Subtract the second reading from the first and divide by three to arrive at the diameter wear. The amount of wear should not excced 0.005 in. (.1270 mm) .
Excessive wear will necessitate reboring and the fitting of oversize pistons which are available in oversizes of + 0.010 in. + 0.020 in. + 0.030 in. and + 0.040 in. The standard and oversize bore measurements are listed below:

| STANDARD: | 2.8750 in. to 2.8758 in. 73.025 mm to 73.045 mm
| + 0.010 in. oversize | 2.8850 in. to 2.8858 in. 73~279 mm to 73 299 mm
| + 0.020 in. oversize | 2.8950 in. to 2.8958 in. 73.533 mm to 73.553 mm
| + 0.030 in. oversize | 2.9050 in. to 2.905S in. 73.787 mm to 73.807 mm
| + 0.040 in. oversize | 2.9150 in. to 2.9158 in. 74.041 mm to 74.061 mm

### SECTION C13

### REMOVING PRIMARY CHAINCASE

To remove the engine or gearbox from the mounting plates or from the frame it is necessary to dismantle the primary transmission completely but the engine/gearbox transmission assembly can be removed from the frame as a single unit. Dismantle the outer primary chaincase as follows:
1 | Remove the three nuts and plain washers securing the left hand foot rest complete with brake pedal and stop switch. It is unnecessary to disconnect either the stop lamp leads or the rear brake cable and the pedal assembly may be allowed to hang down clear of the primary chaincase.
2 | Place a sufficiently large drain tray beneath the chaincase to receive all the chaincase lubricant. There is no drain plug to the chaincase thus as the chaincase joint is parted, the chaincase will drain very quickly.
3 | Remove the centre sleeve nut which secures the outer chaincase and by rocking the chaincase slightly to clear the locating dowels top and bottom, lift the outer chaincase clear.

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