A Six-wheeler Conversion with Four-wheel Drive
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ANNOTJNCEMENT is made by E. Boydell and Co., Ltd., successors to Muir-Hill (Engineers), Ltd., Elsinore Road, Old Trafford, Manchester, of a useful and simply designed attachment for converting orthodox four-wheelers into rigid six-wheelers, the principal feature being that for use on soft or slippery surfaces it is possible to connect the trailing to the driving wheels by means of roller chains so as to obtain the superior tractive grip afforded by four-wheel drive.
In the case of a vehicle equipped with single tyres the chain sprockets are located outside the wheels, but where twin wheels are fitted the sprocket is mounted between the inner and the outer wheel on each axle. To ensure satisfactory operation of the chain drive the distance between the wheel centres must, of course, remain constant, irrespective of spring deflection; yet provision has to be made for easy adjustment of this distance when it is necessary to take up chain stretch.
These points have been provided for in the case of the Muir-Hill design by employing substantial cast-steel torque arms, one at each side between driving and trailing axles. Each torque arm incorporates a simple adjustment device for obtaining the correct chain tension.
A point worthy of note in connection with the „chain drive to the rearmost wheels is that, whilst the differential action is available, there is not likely to be much trouble in the way of wheelspin, because of the better grip obtained by linking the two wheels on each side.
The suspension is of the kind in which one inverted semi-elliptic spring, pivoting centrally about a frame crossshaft, is employed at each side of the chassis. Instead of being shackled to the axle, these springs are supported at their ends on hardened-steel rollers, which are bronze-bushed, so permitting a desirable flexibility. The location of the bogie is obtained by means of silicomanganese spring-steel radius rods, one extending forward and upward on each side from the driving axle to a bracket on the frame-member. These members transmit torque and brake reaction.
We are informed that the Bedford chassis, complete with the conversion, including the chain drive, and equipped with 32-in. by 6-in. tyres (twin rear
tyres), is listed at £366, the rated payload capacity being 4 tons.
The Bedford frame is not cut or altered in any way, so that the conversion could be detached and installed in another chassis. The rear axle is a heat-treated, high-tensile, alloy-steel unit and carries Timken tapered-roller bearings for the wheels. Bendix DuoServo 14-in. by 2-in, brakes, with flexibly enclosed cable operation, are fitted to the trailing wheels.