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THE DEVELOPMENT OF THE 25-CWT. GUY.

3rd June 1924, Page 10
3rd June 1924
Page 10
Page 10, 3rd June 1924 — THE DEVELOPMENT OF THE 25-CWT. GUY.
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Full Details of the Modifications in a Successful Chassis.

THE 25-CWT. Guy chassis, capable of carrying a gross load, including the ;Jody, bf 32 cwt., has been on the market for a few months, and has now settled down into its final form, various modifis cations having been made as experience has been gained in the operation of the vehicle; for instance, tests carried out under full load over extremely hilly ccuntry in Devonshire led to an increase in engine size from that first adopted. Users have been extremely satisfied with the vehicle; the War Office has recently placed an order for 40 of this type, whilst there have been repeat orders from large users, including users overseas.

The chassis is designed for fast vans and ambulances, and can be supplied equipped with solid tyres or pneumatics. The total weight of the chassis, complete with pneumatic tyres, is 25 cwt., so that, vvhilst ample strength is given wherever renuire.d, there is no undue weight anywhere.

Goy Motors, Ltd., have always been noted for the three-point flexible suspension of their engine and gearbox. They have adopted this suspension oa every one of their chassis, and it is to be noted that the War Office now stipulates for three-point suspension on the subsidy models, also for oil lubrication to all parts, which was another feature introduced, before the war by Guys. Ou the 25-wt,, as an examPle, no grease is employed anywhere.

The engine utilized is 18 h.p., four'cylindered, with a bore of 88 mm. and a stroke of 120 rum. There is no doubt that a considerable gain in efficiency is obtained by the special form of cylinder head and the special disposition of the valves, which latter are inclined at a considerable angle to the vertical axis of the cylinder. The head is in one piece and is water-jacketed everywhere, including round the bosses for the sparking plugs. The fan is carried on the cylinder head, being mounted in an eccentric spindle on ball bearings. The shape of the combustion space very closely approaches the ideals which have recently been laid down by prominent designers and, as the power output for the cylinder volume swept out is rather above normal, it is evident that in a Guy engine the power-weight ratio is particularly good.

• The camshaft is placed in the normal position, but., operating, as it does, the valves through bell-crank levers, and the valves being inclined, as already mentioned, the accessibility of the tappets is quite out of the ordinary. It• would seem that all the advantages of the overbead-valve engine, with none of the disadvantages of complication have been attained in this design. The valve tappets and rocker-arm bearings are thoroughly lubricated by spray from the base chamber, and they are well protected by covers.

The crankshaft is a very stiff proposition, 'being carried in three bearings, lubrication -being effected by pressure to troughs which feed the main bearings, connecting rods, camshaft, and all other moving parts. Any chance of stoppage of oil flow by reason of restricted area of cross-section of pipe or of loss of indi 1326 cating pressure is ter t carefully avoided. The filter is extremely accessible for cleansing. • The. engine develops 24 h.p. at 1,000 r.p.m.,and 33h.p. at 2,000 r.p.m.

Fuel is fed through a Zenith horizontal carburetter, and there is ample accessibility to every detail, the magneto being at the right-hand end of the front cross-shaft and being driven by a Simms coupling, thus making the adjustment of the timing a simple proposition. The engine is cooled thermo-siphonically.

The clutch has a large single plate, faced with Raybestos riveted to the driven disc. Pressure is applied through four clutch springs, and the pit protecting the clutch gear and serving to connect the base chamber of the engine to the gearbox casting is open to the centre of the shaft line.

The gearbox, as we have said, is bolted .unit-wise to the clutch housing, combined radial and thrust bearings being employed for the clutch-withdrawal gear. Four speeds are given, direct being I. to 1, third 1.76 to 1, second 2.43 to 1, and first 4.14 to 1. The sliding shaft for changing the gears is mounted in a turret, and operates in a gate. The gearbox is well designed, with short stiff shafts on ample bearings. On the gearbox casting there is formed a facing to carry a tyro inflator, should one be required. .

The drive is taken through a hollow propeller shaft, of large diameter to pre7 vent whipping, with a flexible universal coup:lite -an each end, and thence to a worm-dr:Yen back axle, the forging being by Kirkstall, With worm and worm wheel

by Thend Brown and Sons, and the differentials gear by Guys themselves. The rear springs are underslung, and the pressed-steel wheels are carried on floating bashes lubricated from the axle.

A little refinement—and there are many about the 25-cwt. Guy—is to be found in the series of serrations milled at, the end of the brake camshaft; so that a very fine setting can be secured when first assembling the brake gear, also When it is necessary to take up weaa, whilst yet a further refinement is the employment of a floating tongue in the brake cam shoes, toensure that both shoes shall act equally.

Prevision is made for taking up wear on the steering-gear arm by varying the depth of meshing of the worm and worm wheel by the rotation of an eccentric bush carrying the worm-wheel shaft, whilst the worm-wheel boss has four keyways so that the steerinlg arm can be mounted in any one of four positions, whilst, finally, to cover the last requisite in steering-gear adjustment, provision is made for taking up backlash in the worm thrust.

The tyre equipment consists of 75, 'MM. tyres .on. 720 mm. rims at -the front, and 80 mm. twins ma 720 mm. rims at the sear, Dunlop s being fitted.

The overall length of the vehicle is 15 ft. 4 ins., wheelbase 10, ft. 8 ins., ground clearance 9 ins., and track 4 ft. 8 ins., whilst the length of the space from the dash to the end of frame is 11 ft. 9 ins.

This particular chassis is now selling at 2585 mounted on solid tyres, and £405 mounted on pneumatic tyres.

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Organisations: War Office, US Federal Reserve

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