SECTION F2
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ISOLASTIC ENGINE MOUNTINGS
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The Norton Isolastic principle built into the
Commando couples together the engine, transmission,
swinging fork and rear wheel. This assembly, parted
from the main frame is seen clearly in Fig. F3.
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Isolation of the engine transmission swinging
fork and rear wheel is achieved by the use of
resilient mountings shown as A, B and C. Unlike
earlier attempts at rubber mounting, the Commando
is unique in that the swinging fork is mounted on
the engine cradle and thus isolated from the main
frame. This prevents twisting between the engine
and rear wheel sprockets under load which would
otherwise cause premature chain wear or
displacement of the chain.
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The power unit in its mounting plates oscillates
on the rear mounting (B) which has three bonded and
two buffer rubbers.
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This arrangement provides maximum support,
particularly to the swinging arm and rear wheel,
whilst isolating the power unit from the frame.
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The front mounting (C) controls the degree of
movement of the power unit on the rear mounting and
the two bonded and two buffer rubbers allow more
flexibility than does the rear mounting.
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Both the front and rear mountings incorporate
polyurethane thrust washers to permit side play to
be kept within very restricted limits without
transmitting engine and transmission vibrations to
the rider. The degree of side play is controlled by
shims to enable the figure to be kept within design
limits even after considerable mileages.
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The engine head steady (A) completes the
triangular formation of the resilient mountings and
controls lateral movement of the engine unit in the
frame. The insulating rubbers are fitted between
the side plates and frame tube.
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