SECTION C41
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CHAINS
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It is important to maintain the correct chain
tension since if the chain is too tight the engine
and gearbox bearings will be pre loaded in the case
of the primary chain and the gearbox and rear wheel
bearings will be pre loaded in the case of the rear
chain. Pre-loading will inevitably cause premature
bearing failure. Conversely, if the chains are too
slack then premature wear is inevitable on the
sprocket teeth.
The primary chain operates in an oil bath formed
by the primary chaincase and requires no
lubrication from an outside source providing the
chaincase level is maintained. The rear chain is
lubricated automatically from the oil tank via a
restrictor located to the rear of the tank.
However, the rear chain is not fully enclosed and
from time to time requires cleaning and lubricating
manually.
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Chain Serviceability
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Both in the case of single row (rear) chain and
triple row (primary) chain, chain length extention
of 2% is permissible before the chain is considered
to have reached the end of its usefulness. This
figure presumes that extension is checked only when
the chain has been cleaned thoroughly and that any
chain showing evidence of broken rollers has been
discarded.
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Primary Chain Adjustment
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The separate gearbox design of the Commando
permits adjustment by the medium of pivoting the
gearbox on the bottom bolt and there is no
necessity for a slipper type tensioner. Due to the
high power output of the Commando and Combat
engines the correct adjustment procedure must be
followed to prevent subsequent gearbox movement in
service. Proceed as follows:
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1
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Check the total up and down movement on the
primary chain top run. This is felt by the finger
when the upper centre inspection cap is removed
from the chaincase. If incorrect, proceed to (2).
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2
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Slacken the gearbox top fixing bolt "B" |(see
Fig. C48). Note that nut on left is captive and
must not be turned.
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3
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Slacken the nut on the gearbox bottom bolt.
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4
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Slacken the front nut on the adjuster eyebolt,
two or three turns.
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5
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Tighten the rear nut on the adjuster eyebolt
until, with the finger, the chain can be felt dead
tight.
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6
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Now slacken off the rear nut and carefully
tighten the forward nut until there is total up and
down movement of 3/8 in. (9.5 mm).
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7
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Tighten securely the rear nut to lock the
assembly and recheck the adjustment in at least
three places. Should there prove to be a tight
spot, readjust to total up and down movement of 3/8
in. (9.5 mm) at this point.
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8
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Tighten the gearbox bottom bolt nut. Lubricate
the thread of the gearbox top mounting bolt, fit
the nut and secure to 70 Ib. ft. (87 in. Ib., 9.678
kgms.) torque from the right side. Note: On 1972
and later models, do not attempt to turn the nut at
the left side of the top bolt - this is spigotted
to prevent movement.
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