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Arrol-Johnston Motor Omnibuses.

9th November 1905
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Page 10, 9th November 1905 — Arrol-Johnston Motor Omnibuses.
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The Famous Paisley Works Turn

Out a Machine Embodying Important Departure,

One of the most interesting of the new vehicles which are being pushed forward to be in readiness for the forthcoming Olympia Exhibition is the Arrol-Johnston 24-30h.p. double-deck omnibus, made by the New Arrol-Johnston Car Company, Limited, of Underwood, Paisley. This company, which is one of the oldest in the motor industry, is bringing its extensive knowledge of commercial motors to bear upon the larger and more powerful public service vehicle. The machine in question will embody several features of interest alike to present users and potential buyers, and it must be remarked that Mr. John S. Napier, the winner of this year's Tourist Trophy Competition, is responsible for the design and production in question.

The engine has four vertical cylinders, and gives out 24h.p. at a normal speed of 950 revolutions per minute. It is constructed so that all the working parts are covered up, and run in oil-tight casings. The design allows of easy access to all working parts, and an inspection can be made with a minimum of trou b I e. The gear wheels for

driving the camshaft, water-circulating pump, and the armature shaft of the magneto are completely enclosed, whilst the camshaft and its casing are so constructed that they can be removed in one piece; this enables any necessary repairs or renewals to that part to be made without keeping the vehicle off the road, by promptly fittinga new

one in its place. The bottom of the crank-case can be removed for inspecting the brasses, without disturbing the

main bearings, as these are attache to the upper portion. The crar. chamber is made oil-tight by placir the bearings completely within ?. The four cylinders are cast separately : the cylinder heads and valve chests are not cast in one with the cylinders, but are attached to them by six studs. This system allows a worn or broken valve seat to be replaced by a new one with a minimum of trouble and without having to substitute a new cylinder casting. The material used in the construction of the cylinders, pistons, and combustion chambers, is made at Paisley from a close-grained crucible cast iron, which metal has a long life and is practically free from wear. The inlet valves are placed over the exhaust valves, which arrangement allows a minimum of wall surface and gives a nmaximum compression space;

all valves are mechanically operated. The crank-case is of a special type of aluminium alloy of high strength, and the crankshaft is suspended from the top half by means of the bearings, whilst the bottom portion acts as an oil retainer, and also serves to hold the oil-distributing

pump--which is driven off the crankshaft--in place. When the bottom half of the chamber is removed, the whole mechanism is exposed to view. The crankshaft is machined from a solid forging of nickel steel, and all the main bearings are machine-ground. The camshaft is turned from a solid piece of tool steel, the cams being cut by machinery, and the rods which operate the inlet valves also actuate the make and break for the low tension magneto ignition. The trip motion is very quick in action.

The governor is a patented and unique type, and is adjustable at will, It is operated by the varying suction caused by the engine, and is capable of working at any speed from 200 10 1,200 revolutions per minute. Governing by hand is arranged for by the action of a simple throttle valve, which not only shuts off the mixture, but alters its quality at the same moment ; further, when the engine is used as a brake, it admits pure air to the cylinders, The cylinders are by this means thoroughly scavenged when the vehicle is running down a declivity, and this prevents any drawing of the lubricating oil into the combustion chamber. The engine is lubricated by a force pump, of the intermeshing cog-wheel type, through ducts in the crankshaft ; this is the same system which is successfully used in modern high-speed steam engine practice. It is only necessary to fill the crank chamber to a certain level, indicated on a gauge, and the engine will then run for a day without further attention. This method of lubrication eliminates a smoky exhaust. Low tension magneto ignition is fitted, and the company manufactures its own sparking plugs, which have been proved to run for a long period without repairing. For ease in starting up the engine, an auxiliary battery and coil system is supplied.

A Heie-Shaw metal-to-metal clutch is fitted, and it is so arranged that there is no end thrust on the crankshaft. This type of clutch, by its gentic action, does not strain the gears or tyres, thereby increasing their life. The gear-box has four speeds forward and a reverse; the fourth, or top speed, having a direct drive. Three-point suspension is employed, in order to do away with all strains due to twisting of the frame on rough roads. The gear-box has been the subject of much thought, and has been designed to allow the necessary changes of gear without noise_ The revolving mass of the first-motion shaft has been kept so small that there is no difficulty in synchronising it with the speed of the second-motion shaft. All the bearings are of the roller type, of a pattern which has given satisfaction to the ArrolJohnston Company for some considerable time, and these

bearings are used in preference to ball bearings. Lubrication of the gear-box is automatic ; the method of application being as follows :—A well is made in each end of the casing with ducts leading to each bearing, and the wells and ducts are connected by woollen strands, so that the bearing has a constant supply of clean oil, and one which does not run short as long as there is any oil in the gearbox. This system has been in use for nine years without a hitch.

Power is transmitted, from the gear-box to the driving wheels, by a short longitudinal cardan shaft, an enclosed differential shaft, and roller chains. The special universal joint at the gear-box end of the cardan shaft is designed so that all driving efforts act in one plane, in order to avoid lack of uniformity in the speed of the shaft during a revolution, and this joint is protected by an aluminium cover filled with grease and oil. The rear end of the cardan shaft has a combined spring and universal joint drive; springs in compression are held in a circular disc casting, and the drive is effectively transmitted, even if a spring

breaks. The diffe -ential shaft revolves in a strong casing, which is split lonwtudinally instead of vertically, thus allowing the top cover to be removed for inspection of the gears or other purposes. The shaft and its casing are supported by tubular radius -ods, and the journals run in roller bear-. ing-s. It will be seen from the general arrangement, at the foot of page iss, that none of the weight of the transmission is taken by the differential shaft itself, but that it is all carried by the roller bearings attached to the outer casing; the shaft only takes the stresses due to torsion.

The frame is built of channel steel of a heavy section, to which the cross members are riveted, and to strengthen it still further diagonal angles are riveted to the centre of the frame, making the whole very rigid. The front axle is a solid steel forging, and every endeavour has been made to keep the centre of the wheel bearing as near the vertical pivot as possible, to do away with as much leverage as possible, and to make the steering easy. The back axle is of ample strength for the work required of it, whilst the method adopted for its suspension is interesting. The back springs, of which there are three, viz„ two side ones, and one of the transverse type, are fixed in the usual manner, but they are so designed that they have no duty to perform other than taking up the weight of the body with its passengers. No stresses or road shocks are conveyed to the main frame through the springs, as all the strains set up by the transverse rocking motion of the body are dissipated by means of a parallel device which connects the framing to the axle. The veh:ele is fitted with two brakes. The first, applied by a foot pedal, acts on drums on the differential shaft ; the second, worked by a hand lever, operates on the inner side of the echain sprocket rings bolted to the hubs of the driving wheels. The radiator is of the gilled tube type, and is made specially strong to withstand the severe strains put upon it; the joints, where possible, are riveted. A gear-driven pump of the spur-wheel type is fitted for circulating the cooling water, , and the fan is integral with the flywheel. A petrol tank is carried beneath the driver's seat, and precautions are taken to see that the spirit is efficiently strained before passing to the carburetter. The road wheels are artillery pattern, and have hickory rims, and English oak spokes. Solid rubber tyres are fitted, those on the back wheels being of the twin variety. The gearing throughout is machine cut, and all plain bearings are of hard gunmetal. An important feature is the interchangeability of all parts, and this is acknowledged to be one of the most necessary points in present-day motor omnibus construction. The vehicle will repay a careful inspection, and we anticipate that the makers will find numerous enquiries, and not a few orders, fall to their lot at the coming show. No more promising omnibus chassis has come under our notice.

We have received from E. and F. N. Spon, Ltd., of 57, Haymarket, S. %V., a copy of a new English-French and French-English dictionary of the motorcar, motorcycle, and motor boat. The dictionary is the work of Mr. Frederick Lucas, and is published at 5s. net. The object of this neatly compiled book is to assist those interested in the motor industry and pastime to read the foreign technical literature devoted to the subject. The technical terms used in the various journals, and the catalogues of the leading English and French makers, have been translated into the respective languages; the book should, therefore, be of service to both the user and the manufacturer. The fact that no guide to the gender of the various French terms given has been included in the volume, whilst unnecessary to meet the avowed object of the authors, seems to us to limit the book's sphere of usefulness to the few who are readers of the technical literature in question. For those—the great majority of motorists—who would wish to use the book as an aid for other purposes, such as visits to works in France, or when touring on the Continent, the scheme of the dictionary is hardly complete.


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