SECTION C12
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CYLINDER REBORING AND OVERSIZE PISTONS
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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).
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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) .
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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:
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STANDARD:
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2.8750 in. to 2.8758 in.
73.025 mm to 73.045 mm
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+ 0.010 in.
oversize
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2.8850 in. to 2.8858 in.
73~279 mm to 73 299 mm
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+ 0.020 in.
oversize
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2.8950 in. to 2.8958 in.
73.533 mm to 73.553 mm
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+ 0.030 in.
oversize
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2.9050 in. to 2.905S in.
73.787 mm to 73.807 mm
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+ 0.040 in.
oversize
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2.9150 in. to 2.9158 in.
74.041 mm to 74.061 mm
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SECTION C13
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REMOVING PRIMARY CHAINCASE
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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:
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1
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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.
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2
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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.
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3
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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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