Morgan three wheeler bevel box.
The Morgan three wheeler is fitted with a 90 degree bevel box which turns the rotary Motion of the prop shaft sideways to get round the rear wheel and then uses a toothed belt final drive to the rear
wheel. The bevel box is subject to many forces due to the nature of its operation. It will, for example, lift up at the front due to the input shaft pinion wanting to climb up the teeth of the crown wheel.
The Morgan three wheeler bevel box must therefore be very strongly and rigidly mounted. The bevel box is inherently noisy, mine emits a loud whine which is road related and loudest at speeds above
40 mph. It should be noted that road noise from the rear tyre is also quite obvious due to a lack of sound insulation in the vehicle - it is, after all, a sports car! The NVH kit was fitted to isolate the noise
transmitted from the bevel box through the vehicles chassis. My investigations in to the various problems on my Morgan three wheeler led me to experiment with a single, fail safe, rubber engine
mount under the nose of the bevel box. The forces produced on hard acceleration almost turned the mount inside out! This upward force is directly proportional to the forward propulsive force being
applied to the vehicle, reduced by the gearing of the bevel box and final drive but increased by the ratio of lever length between the rear wheel radius and the distance between the bevel box input
flange and the centre of the crown wheel. The bevel box mounting must therefore be very strong, very rigid and also provide sound isolation from the chassis.
The P.G.Bleazey drive train upgrade kit uses inserts in the Centa coupling of modified shape to reduce the free play. The shock absorption is achieved by distortion of the inserts not by rolling action.
The amount of distortion can be controlled by changing the shape of cut outs in the inserts and also by changing the hardness of the polyurethane material from which they are made.
The ones used in the P.G.Bleazey drive train upgrade kit are true prisms and do not allow for misalignment, this function is not needed in the Morgan three wheeler application.
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