A New 58 b.h.p. Dennis Rubber-tired Tractor.
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Particulars of a Novel Production from the Guildford Works, which is to be Used for Hauling and Shunting on the South African Railways,
We have had occasion to refer many times to the remarkable degree of enterprise and activity prevailing at the Dennis factory, and our readers are fully aware of the prominent position which Dennis Bros. (1913), Ltd , occupies in the industry to-day. This week we arc enabled to publish still further indication of the company's progress.
We need hardly mention that the Guildford works, are busy night and day building machines for the War Department. The particular information forthcoming refers to a novel type of rubber-tired tractor, which will shortly be despatched to South Africa. Immediately following the machine's completion a few days ago, a " C.M." representative was afforded an opportunity of inspecting the tractor, which has successfully undergone some severe tests.
Well-known Dennis Features are Incorporated.
The vehicle embodies many features which have made Dennis lorries so successful in service. Its unique general lay-out, however, differs much from any of the productions which have, up to now, been listed by the company, and its introduction will, we feel sure, evoke no small amount of interest. The tractor is the outcome of a scheme submitted by the Engineer to the South African Railways, and it is the forerunner of several other machines of similar type to be shipped to that colony. In addition to hauling, the equipment is to be used for shunting purposes.
One of the chief problems with which the tractor designer is faced is the necessity for bringing as much weight as possible on to the driving wheels, consistent with the particular type of machine which he has in view. That the constructors of the tractor under present consideration have admirably succeeded in this respect will be readily understood when it is stated that, although the total running weight of the machine is only 3 tons 15 cwt., it has comfortably
hauled 7.5 tons up an incline at 3 m.p.h., over a test-course which included the well-known Hog's Back, and, as many of our readers are aware, the stiffest bit of climbing over this route embodies a gradient of 1 in 9.
In studying the general arrangement of the tractor, the first thing which one will probably notiee is the disposition of the power unit. It is of the four-cylinder vertical type 4and is mounted somewhat amidships in the frame to the rear
of the driver, and the clutch end of the crankshaft is adjacent to the back of the driver's seat. The bottom part of the crank chamber is almost on a level with the top of the main-frame sides, constructed of rolled channel steel.
The Subvention-model Engine.
The engine has a bore and strq.ke, respectively, of 110 mm. and 150 mm., and when running at normal speed it will develop 38 h.p. on the brake. It is a subvention model, consequently it is cooled by means of a large-sized 'centrifugal pump. Immediately forward of the rear axle is mounted a Solex radiator, which, of course, is a type of cooler well suited for Colonial service. The air-circulating fan is driven through a leather universal joint. The engine of the first tractor to be put through embodies a separate oil tank in its lubricating system. In subsequent models, however, the main oil supply will be self-contained in the crankcase sump. The necessary oil level for the reciprocating parts will be maintained with the aid of a specially-shaped baffle plate fitted separately in the main oil receptacle. Two largesize filters are incorporated, and, through these, the overflow of lubricant has to pass on its way to the sump. The new system will be entirely free from pipe lines and unions.
The combustion heads of the cylinders are of the T pattern, the inlet and exhaust valves being located on the near and off side, re
spectively. There is a duplex induction system, to enable the engine to be run either on petrol or paraffin. Both carburetters are of the well-known White and PoPpe construction ; that which supplies
the engine with petrol vapour is mounted directly on the inlet pipe, on the near side of the engine, whereas the paraffin carburetter is fixed to the end of a copper induc
tion pipe which passes through the main engine exhaust manifold. This eminently satisfactory system of paraffin vaporization is the White and Poppe principle.
A Single-lever Controls the Duplex Fuel-system.
A single lever, mounted to the steering column, and direct), underneath the hand wheel, serves to control either the petrol or paraffin supply. The engine, of course, is fitted with a governor ;: this is contained in the same cover which encloses the timing gears.
The engine power is first transmitted through a Ferodo-lined clutch to an arbor shaft, which runs under the driver's seat and parallel with the centre line of the chassis. The necessary end thrust for the clutch is maintained by three coil springs mounted on the exterior of the friction member, and, therefore, quite accessible for any necessary adjustment. The friction member has a machined facing on its outer surface, and its large diameter affords quite a satisfactory clutch brake; to effect this two Ferodohned segments are brought into contact when the clutch pedal is depressed. .The clutch shaft proper is a steel stamping, which also serves as a spigot guide for the crankshaft ; it has three arms bolted up to a leather ring universal joint. From the arbor shaft the drive is transmitted through a Coventry silent chain ; this latter is mounted at the forward end of the chassis and immediately behind the dashboard. Running parallel with the universal-jointed shaft pre A20 viou sly referred to, and practically on a level with the centre-line of the rear-axle worm, is an additional arbor shaft, which is connected up by two universal joints to a four-speed, subsidy-type gearbox. The malleable cast case which covers the gear set is mounted on a sub-frame of rolled-steel channel. Its large-sized inspection cover and the oil filler are readily detachable, and quite clear of control rods. A loco-type of font brake is mounted immecliatt13 behind the gearbox, and its cast-iron shoes are contracted by the aid of a small transverse worm shaft. Behind this brake is fitted the pin-type unive'rsal joint of the propeller shaft proper. This component is hol..low, and is machined out of hightensile steel. At its rear end it is coupled up to the well-known Dennis worm axle, the final ratio of which is 12 to 1. Loco-type Horn-brackets take the Driving Torque.
The rear springs are shackled at both ends, and their service is solely for suspension, the driving torque being transmitted through loco-type horn brackets and swivel blocks embodied in the back axle construction. The hand-operated brake takes effect on cast-steel drums bolted directly to the rear road wheels. All four wheels are quite unique in their design, as will be seen from some of our illustrations; the spokes are formed of mild-steel channel. These were specially constructed by the Shrewsbury and Challiner Tyre Co., Ltd. The two front wheels take 900 mm. by 120 mm. rubber tires, whilst the dimensions of the rear twin bands are 1220 mm. by 120 mm. With these wheels the ground clearance at the lowest point of the vehicle is 1112 ins., that is at the centre of the front axle ; the rear axle has 13 ins, ground clearance at its lowest point. At the tail end of the tractor is mounted the trailer drawbar and pin ; the latter is provided with two involute springs, one of which is brought into service for hauling, and the other when the machine is buffing.
With regard to seating accommodation, in addition to the driver i there s room for four persons, the rear seat being mounted nearly over the back axle, and with its back towards the driver's seat. The various speeds of which the machine is capable are as follow : first, 2i m.p.h. ; second, 41 m.p.h. ; third, 7 m.p.h. ; and fourth, 111 m.p.h. The latter is a direct drive from the engine. The divided fuel tank has a total capacity of 291 gallons, 21 of which can be paraffin The wheelbase of the tractor is 9 ft., whilst the track is 5 ft. 6 ins. The height from the top of the frame to the ground is 3 ft. 4 ins.