New Tractor with Eight-cylindered Oil Engine
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F.4 MPLOYING the Gardner 8LW eight-cylindered oil engine, a heavy-duty six-wheeler which has been added to the Atkinson range, incorporates a number of other interesting features. The first chassis made to this design is a load carrier, and was built to the order -of a South African operator. Atkinson Lorries (1933), Ltd., Walton-le-Dale, near Preston, intends, however, to offer Ibis new model primarily as a tractive unit, in which form it will have a wheelbase of 12 ft. 2 ins. The model inspected has a wheelbase of 15 ft. li ins.
The gearbox, which is a modified version of that employed on earlier models, is unit-mounted with the engine. All gears, with the exception of first and reverse, are of the constant-mesh type, the box incorporating the Atkinson change-speed mechanism which dispenses with the usual ball-and-socket action.
The Kirkstall doable-reduction axles in the bogie assembly provide a 3.33 to I ratio, the Kirkstall sun-andplanet hub gear of a ratio of 3.17 to 1 giving an overall ratio of 10.55 to 1. Worm centres are 7i ins.
'I imken heavy-duty taper-roller bearings are used at the pivoted point of the bogie balance beam, a feature in design which makes for greater reliability over long periods.
In keeping with the Gardner LW range of engines, this unit has cylinders of 41 ins. (107.952 mm.) bore and 6 ins. (152.4 rum.) stroke, so that the swept volume is 11.2 litres, and the Treasury rating 58 h.p. Dry liners are used, the cylinders being in two blocks of four with four detachable heads each covering two cylinders.
The rating at sea level is given as 140 b.h.p. at 1,700 r.p.m. maximum, but for operation at 2,000 ft. above sea level this unit has been de-rated to 128 b.h p. Embodying the Gardner engine-mounting arrangement, in conjunction with an Armstrong hydraulic damper, the power unit is singularly free from vibration. In its de-rated form the machine is intended for a gross tractor-trailer load of 50tons, . A large radiator with 64 Withnell tubes is fitted integral with a 12-tube engine-oil cooler to which the oil is delivered by an additional pump on the engine. The cooler is mounted in front of the radiator.
Air passing to the engine is cleaned by a large Air-Maze tiller, the normal position for which will be at the rear of the cab. The engine silencer is mounted on the gearbox, so that there is no relative motion between the silencer and the engine.
The drive is taken through a Borg and Beck 16-in.diameter dry-single-plate clutch to an exceptionally compact five-speed gearbox, providing ratios of 7.70, 3.95, 2.62, 1.61 and 1 to I forward, and 7.31 to I reverse.
Parallel and straight throughout their length, the channelsection frame members are 11 ins, deep, with 3-in, flanges, and of a i n gauge steel. There are five deep cross-members bracing the frame behind the gearbox, with a substantial bridge-piece linking the side members on a line with the flywheel housing.
Suspension is by semi-elliptic springs, those on the rear bogie being underslung. Tyre sizes are 11.00 by 20 all round, with twin tyres on the bogie axles.
Braking is by a Clayton-Dewandre air-pressure system, with 5-in.-diameter cylinders on the front wheels, and 6-in.-diameter cylinders at the rear. Air-line pressure is 80 lb. per sq. in. A two-pipe-line system is provided for the trailer, so that the brakes are energized from their own unit. The dimensions of the front drums are 161 ins. by 4 ins., those on the bogies wheels measuring 16-1 ins. by 6 ins. The weight of the chassis is 6 tons 16 cwt. 1 qtr.
Main dimensions of the model inspected are:--OveTall length. 26 ft. 2 ins.: overall width, 7 ft. 71 ins.; front track, 6 ft.4 9116 ins., rear track,. 5 ft. 8 ins. Laden, the frame height is 3 ft. I in.. and ground efearance 11 ins.