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ACHIEVING LIGHTNESS IN PASSENGER CHASSIS.

13th April 1926, Page 23
13th April 1926
Page 23
Page 24
Page 23, 13th April 1926 — ACHIEVING LIGHTNESS IN PASSENGER CHASSIS.
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The Latest Guy Product Which Has Been Designed to Comply with the Proposed Ministry of Transport Regulations.

OF THE various modern tendencies in the design of passenger chassis one which has, perhaps, received as great attention as any other is that making for lightness in construction. In fact, practically all the prominent chassis.,manufaeturers have given this factor special consideration, with the result that most of them now include in their manufacturing schedules a passenger model designed to comply with the proposed regulatious of the Ministry of Transport which, as most of our readers will he aware, provide that a vehicle shall be permitted to travel up to 20 m.p.h. if,it comes within the unladen weight limit of 3 tons 15 cwt. and is equipped with pneumatic tyres.

Guy Motors, Ltd., Failings Park, Wolverhampton, were amongst the first to recognize the importance of lightness in vehicles built for passenger work, and the lightest of their range of such chassis is built to carry bodies which seat from PI to 20 passengers. This model is a representative Guy product and, incorporates many features which are indicative of. the trend of modern :development .in chassis •desiga,•.

Tile engine is a four-cylinder unit with a bore. and stroke of 88. min. and • 120 into. respectively ; it develops 22 h.p, at 1,000 r.p.m. Outstanding characteristics in its design are the patented valve arrangement and the detachable cylinder head. Several advantages are claimed for this form of-lay out, which is said to be an improvement on the ordinary side-by-side or overhead positioning of the valves.

In a sense the---Guy design

is a happy mean between the two forms, for the valve-operating gear is placed at the side of the cylinders although the valves are inclined at an angle, their heads being at one side of the combustion chambers. In this position they are not subject to such,ihigh temperatures as in certain forms of overhead arrangement of the valves and their actuating mechanism. • Moreover, the design enables the sparking plugs to be disposed directly above the centres of the pistons, admittedly a good position.

The valves are readily get-at-able, as are the 'combustion chambers, and both can receive attention by removing the cylinder head, an operation which is quickly and easily performed. If a piston requires examination it can be withdrawn, along with its connecting rod, through the top of the cylinder casting. Twin rubber joints, which are quite separate from the usual gasket, are used to overcome the possibility of water from the cylinder jacketing finding a way into the combustion chambers.

The cooling water is circulated by a centrifugal pump and It passes through a vertical gilled-tube radiator, the top and bottom tanks of which can be easily removed, thus enabling the tubes to be cleaned.

A gear-type pump in the lower half of the crankcase forces oil to the main bearings and to troughs under the connecting rod big-ends. For carburation reliance is placed on a Zenith instrument which is conveniently mounted, as is the magneto, the latter being carried in an extremely accessible position ahead of the cylinder block.

From the engine the drive is conveyed to a fabric-faced cone clutch and a four-speed-and-reverse gearbox which forms a unit with it. A clutch stop facilitates the operation of gear-changing, which is effected by a lever to the right of the driver. The gears and shafts ore of nickel alloy steel and a protecting disc is used to prevent foreign matter getting into the bearings.

A two-piece propeller shaft connects gearbox with back axle, the three joints being of the fabric type, the rearmost of them slides on the shaft. As the third . picture in our group of illustrations on the previous page clearly shows, the shaft is supported in a bearing carried by .a cross-member slightly ahead of the intermediate joint.

' The back axle is worm driven and is of the full-floating pattern ; the worm is below the axle the casing of which is a steel stamping. The whole of the working parts of the rear axle can be removed without the need for jacking up the vehicle or taking off the road wheels and without the afd of a pit. After drawing out the axle shafts and undoing a few nuts holding the lid of the casing the worm wheel can be withdrawn through the top, or, if it be required to remove the whole of the gearing, this can be let down through the bottom of the axle casing.

Oil is used for lubricating the back axle and the reservoir containing it also automatically supplies lubricant to the road-wheel bearings and the semi-elliptic rear springs; the fatter are carried below the axle and thus contribute towards the designer's aim of securing a low loading level.

Both the foot and hand brakes take effect on the rear wheels, separate drums with which the internal-expanding shoes make contact being provided. The shoes are interchangeable. On passenger chassis of many types, even those of the =tallest size, front-wheel brakes are in increasing demand, and to meet this need Guy Motors, Ltd., have arranged that such equipment can be fitted. They offer the choice of front-wheel brakes actuated in conjunction with the ordinary footcontrolled brakes or a vacuum servo motor for assisting,.in their application.

A complete worm wheel and worm are used for the steering, the former being carried on an eccentric bush ; the worm is, of course, adjustable for end-play. The strong tubular side and cross-steering rods form oil reservoirs from which wick feeds lead to the ball joints. A filling orifice is provided to enable the oil supply to be replenished, although this is only necessary after many thousand miles of running.

The front axle swivel pins have renewable bushes, and the wear on the heads is taken by thrust bearings. The wheel bearings and swivel pins are lubricated from the oil reservoir above the swivel.

Steel disc wheels are used, and they are shod with 880 mm. by 120 mm. pneumatic tyres both front and rear, twins being used in the case of the latter.

The chassis frame Ride members are of channel steel. They are downswept at a point to the rear of the engine and upswept to clear the back axle, and at

these points steel plates are employed to give increased strength. The frame members are connected by a series of strong tubular cross-members which stiffen the structure without materially increasing the weight.

Although the new Guy passenger chassis is of very light construction—its approximate weight is 26 cwt.—this factor has not been achieved by sacrificing strength at those points where the k greatest stresses are imposed. It is

equally suitable for bus or coach work within its rated carrying capacity and, so far as light. buses are concerned, should prove exceedingly useful for fast country services on which oue-man-controlled-type vehicles are used.

We can fittingly close by giving a few outstanding dimensions of the chassis. Its wheelbase is 12 ft. 5 ins, and track 5 ft. 1 in., the length of the body space measured from dashboard to end of frame being 12 ft. 9 ins. The ground clearance is 9 ins., and when the vehicle is loaded to its capacity the chassis frame is 1 ft. 9 ins, from the ground, this being sufficiently low to permit the use of bodies with a single step to the interior.


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