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3rd February 1925
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Page 13, 3rd February 1925 — A BUS CHASSIS TO MEET NEW REGULATIONS.
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In Anticipation of the Regulations to be Issued Under the Prfnnised New Motor Law, Dennis Bros., Ltd., Produce a Fast Light Bus on Pneumatic Tyres.

WHILST there has been no official announcement, or even suggestion, of the terms of the regulations governing the construction of passenger service vehicles, which will be issued by the Ministry of Transport under the projected changes in motor legislation, yet, as the result of conferences between the officials of the Ministry and the representatives of the commercial motor industry, very shrewd guesses may be made on essential points. For instance, it is fairly certain that buses which tun on pneumatic tyres and which do not weigh more than 3 tons 15 cwt. unladen will be allowed to speed up to 20 m.p.h. Such an acceleration in traffic will be of obvious advantage to many concerned and the result is that bus-operating companies and municipal public passenger service departments which are increasing their fleets or establishing new ones are asking for vehicles which will permit of advantage being taken of any concessions which are likely to be disclosed when the new regulations are published.

Dennis Bros., Ltd., of Guildford, have been preparing for the demand for fast light vehicles on pneumatic tyres, and have produced a chassis which will fill the need and comply with official requirements, whilst, as a result of bold but wellordered experiment, and taking advantage of the experiences recorded by users of Dennis braes, operating in many parts of the country, a 30-seatei.bus body has been produced that will bring the vehicle within the prescribed limits.

Weight being a vital factor, this may conveniently be dealt with first of all. The chassis is designed for two of the standard Dennis engines—the 30-40 h.p. engine (cylinder bore 105 mm., piston stroke 150 mm.) and the 40-50 h.p. engine (cylinder bore 115 mm., piston stroke 150 mm.). The weights of the two chassis are :— With a 30-seater body the total weight of each vehicle is well within the anticipated limit of 3 tons 15 cwt, The makers have already accepted orders for 15 of these bus chassis for Auckland (N.Z.) Corporation, three of them having been shipped, whilst there are orders in hand from the Aldershot and District Traction Co., Ltd., from another over. seas source and from certain municipal bodies, and yet the existence of the new model has only been disclosed to a few potential customers.

There is little need to go into the details of the components of this chassis, because the standard units of the company have been employed thrOughout, but certain essential facts may be mentioned. The engine (whether of the 30-40 h.p. type or the 40-50 h.p. type) has its cylinders cast in pairs, the accessibility of the arrangement of the magneto, oil pump, carburetter, fan drive and dynamo being very marked. The Clandel-Hobson power jet carburetter is employed, a hotwater jacket surrounding the lower portion of the induction pipe. The power unit is carried in a sub-frame, the arched front cross-member of which is sup ported on a centre pin mounted on the front cross-member' of the frame, whilst at the rear the sub frame is bolted to

another cross-member. The gearbox 77s Supported at three points and has an extended oil filler, the orifice of which is brought out to the line of the frame and is therefore most accessible. As we have mentioned in a previous article on Dennis bus chassis, great pains are taken to secure silence in the transmission, one method employed being to grind all gears after hardening, whilst long service is sought by the use of gears of amiable width and pitch for th.1 stresses they are called upon to undergo.

The clutch is of the external-cone type, faced with Ferodo, the springs being exposed and capable of being readily adjusted. Between the dutch and gearshaft are two fabric disc universal joints of large diameter. The cross-shaft carrying the dutch-operating gear is anchored on hangers with self-aligning bearings, the same device being employed for the cross-shaft carrying the levers operating the rear brakes.

Mounted at the rear of the gearbox is a powerful transmission brake, with metal shoes, although, if it be asked for, the shoes will be equipped with Ferodo linings, the same remark applying to the shoes of the rear-wheel 'brakes.

The propeller shaft is a tube of 3i ins, external diameter. sliding in splines in the forward .universal joint, the diameter being adopted in order to obviate any chance of whirling. The power is transmitted through worm: gearing to the axle shafts. The axle casing carries the weight of the vehicle and its top cover is easily removable without any, need for dismantling the axle or wheels. The cover carries the 'worm and wheel and differential gear, whilst the live axle shafts aye easily withdrawn without retnoving the wheels or jacking up

The frame is of pressed-steel channel section and 6 ins. deep at the deepest part. The rear springs are 56 ins, long by 2iins, wide and have 13 leaves. Under full load they are practically flat, their front ends transmitting the drive and absorbing the torque. The front axle is cranked in order to secure a low frame level.

Grease-guninbrication is adopted wherever suitable, and accessibility to all means of adjustment is a pronounced feature of the chassis.

The wheels are of east-steel, disc type, equipped with 36-in, by 6-in, pneumatic tyres on the . front and 40-in. by 8-in. single pneumatic at the rear, an alternative being 955 mm. by 155 mm. pneumatic tyres all round, twins at the rear and an extra tyre, at the same priee, namely, 1705. With pneumatic tyres, 88 ins. by I ins: at front and 42 ins. by 9 ins, at rear, the price is £15 extra, whilst employing the larger engine :9.44.1s £20 to'the cost. If solid tyresare fitted the price of

the chassis with the smaller engine is £650, or with the larger engine £670. The price includes a lighting set, complete with five lamps, six interior lights, dynamo and battery.

• A few important dimensions are here added :—Whedbase, 15 ft. ; dash to centre of rear axle, 12 ft. 6 ins. ; extreme-overall length, 23 ft. 2 ins.; extreme overall width, 6 ft. 6 ins.;

dash to end of frame, 18 ft. 91 ins.; width of track, 5 ft. 2 ; width of frame, 3 ft. 1 in.; height of frame from ground, 2 ft. 7i ins.; weight, 49icwt.; approximate turning circle, 55 ft.; clearance under rear axle, 101 ins.

The bus body developed at the Dennis works for this chassis is extremely light, a 30-seater with a separate compartment for the. driver, with wide entrance on the rear quarter, with sliding windows (four on each side) and ventilators, weighs ress than 24 cwt. It is, in every way, a shapely vehicle, constructed for hard wear and calculated to give lengthy service, and it is extremely well finished in all

of its details.

Following upon our inspection of the chassis and buses going through the shops, We grasped the opportunity afforded to us to measure the paces of the chassis loaded with test' weights to represent a load of 30 passengers. As there were two observers sitting beside tlie driver, there was a slight

overload in the.. first test, which embraced the surmounting of the hill in Guildford known as Mount Street. This has a gradient of 1 in 6 on the steepest portion and is about 1 in 7 throughput. The chassis climbed this with perfect ease on second gear, the engine actually accelerating continuously after the change from third gear to second gear. Over the brow of the hill a very steep drop to the Godalming road presented itself, the brakes doing their work smoothly and efficiently. Subseiluently the chassis was driven over the Hog's 13aelt, the observers following closely in its track in a car ecuipped with a speedometer. The readings of the speedometer hand, however, did not accord with our ideas of the speed of the ear at any moment and we had resort, therefore, to the orthodox method• of timing the speed between the milestones, finding that the car was travelling at a higher speed than that indicated. However, as it happened, there was a considerable amount of traffic on the road proceeding to and from Guildford, visibility was low because of the presence of fog,which became denser as we got farther away from Guildford, whilst every ear seemed to be travelling slowly because of the slippery state of the road. We recorded no speed from milestone to milestone higher than 26 miles an hour, but it was hopeless trying to open out at all, for at every attempt to speed up another vehicle would loom up through the fog, necessitating slowing down before passing it. The makers claim that a speed of 40 miles per hour can be attained and maintained, thus showing that there is an ample reserve of power for use in hilly country.

The aim of the makers of Dennis buses is to ensure long life, a minimum of wear in the moving parts and freedom from trouble, so that a bus may be kept on the road for a whole year without the loss of a day, and even at the end of a year shall not call for overhauling.


Organisations: Ministry of Transport

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