Norton Commando Workshop Manual

## Frame and Ancillaries

# F

### SECTION F2

### ISOLASTIC ENGINE MOUNTINGS

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.
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.
The power unit in its mounting plates oscillates on the rear mounting (B) which has three bonded and two buffer rubbers.

This arrangement provides maximum support, particularly to the swinging arm and rear wheel, whilst isolating the power unit from the frame.
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.
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.
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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