The S.M.T. Three-tonner.
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An Interesting Worm-driven Chassis, with a Chain-drive Gearbox, which has been Developed as the Result of Practical Experience.
During the past month the Scottish Motor Traction Co., Ltd., has received orders for 70 of its own design of three-ton chassis, and that surely is sufficient to warrant our devoting space, even with our pages so congested as they are at the present time, to a brief description of a chassis which has thus earned practical approval at the hands of users—the best of all recommendations.
We reproduce, as an illustration below, a photographic side view Of this machine, It has been designed throughout by Mr. W. J. Thomson, M.I.A.E., the general manager of the company, of which, by the way, the offices, works and garage are at Fountainbridge, and the showrooms at 150, Lothian Road, Edinburgh. It may be taken that the machine has been produced as the result of definite experience in service, and, indeed, it has been in operation in considerable (lumbers, during the past twelve months, by the company itself. The principal points which have been kept in view are the excellent ones of simplicity, accessibility, fewness of parts, and silence.
It will be seen, from an inspection of the illustration b,elow, that the chassis is of the overtype pattern —that is, with the engine below the driver's footboard, a class of design which yields advantages as to amount of available body space, distribution of weight, etc., which are well known and widely appreciated. The driver's position is alongside the engine.
A four-cylinder, vertical Tylor engine is employed, and this is of the considerable capacity of 45 b.h.p., the cylinders being 5 in. bore, whilst the stroke is 6 ins. The Tylor design of engine is well known, and we need not deal with it in detail at the present time. Suffice it to say that the ignition is by Bosch high-tension magneto, and the carburetter is of the Claudel-Hobson type. A centrifugal governor is fitted if desired. Another desirable accessory is the provision of half-compression mechanism to facilitate starting. The radiator is of a special design, with cast headers and tubular centre, and special attention has been given to the necessity of ensuring equal expansion throughout. A belt-driven fan and a centrifugal circulating pump ensure, in combination with this radiator, adequate cooling arrangements.
The clutch is of the usual conical, leather-faced type, and it transmits the engine power through a short shaft, with universal leather couplings, to a. tourspeed gearbox, in which the top speed is direct. The other forward speeds are by silent chains, whilst the reverse is by ordinary spur pinion. The final drive is by a steel worm and phosphor-bronze worm wheel, the short transmission shaft between gearbox and back axle being interchangeable with that between engine and gearbox.
The whole of the final drive and differential gear can be lifted clear of the axle after the differential shafts are withdrawn, so that the design of the back axle component is in accordance with the latest practice. The two brake systems act direct upon two different sets of brake drums bolted direct to the rear ; there is no propeller shaft brake.
The wheelbase of this chassis is 13 ft. 6 ins., and the wheel track is 5 ft. 6 ins. The length behind the driver's seat is 18 ft. 3.1 ins, and the width of the frame is 3 ft. 6 ins,
The price of the chassis, with tires, is .625, and the company is in a position to offer machines fur early delivery, especially to those who are desirous of replacing their commandeered three-tonners. We commena this machine from personal knowledge.