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EVOLVING A LUXURY COACH CHASSIS.

2nd February 1926
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Page 23, 2nd February 1926 — EVOLVING A LUXURY COACH CHASSIS.
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Some Interesting Facts Concerning the Latest Guy Low-framed Chassis with Six-cylinder Sleeve-valve Power Unit.

'DOR MANI years Guy Motors, Ltd., of Wolverhampton, have been catering for the needs of these operating coaches and publicservice passenger vehicles. They have consequently gained a most valuable experience in this connection, and that they have made extensive use of the knowledge thus gained in the design of their chassis and eomplete vehicles is proved by their ever-increasing popularity. Guy vehicles possess many exclusive features which make a strong appeal to those who desire powerful. smooth-running coaches and buses which will have a long-wearing life and be easy to inspect and repair when necessary.

It may be said that their latest model, which is known as the Premier Six, embodies these features to a remarkable extent. Quite probably not all buyers will want a vehicle with a six-cylinder engine; for these there are other models almost identical in their leading characteriStics with that with which we are now dealing, but having four-cylinder power units; but there is certainly a tendency towards providing the best possible type of vehicle for the work, Particularly in the case of coaches where the comfort of the passengers has to be considered primarily.

In the U.S.A., where long-distance coaching is becoming the vogue, almost eight out of ten passenger chassis have six-cylinder engines and there is an increasing call for them in Britain. A buyer who, is willing to pay a little more for a chassis of this type expects something really good, particularly as regards vibrationless torque and silence, and it is for this reason that the makers have adopted the Knight steel-sleeve unit. The famous Guy engine, with its special arrangement of poppet valves and efficient combustion chamber, gives practically a maximum of economy, but a little of this has to be sacrificed to luxury in the new type.

There is a distinct call from overseas for the new chassis; contracts were actually lost before its production

because the makers had none of this type available and now it is in being there has been an immediate call. For instance, 28 have been ordered for Rio de Janeiro, and this after some of the American personnel of the operating company had spent seven months visiting factories in America, on the Continent and here. Nine are being built for Keith and Boyle (London), Ltd., the well-known proprietors of the Orange Coaches, whilst 35-seater singledeck buses on this chassis have been ordered by the Liverpool Corporation.

One of the main features of the new chassis which requires emphasising, as some doubts have been thrown upon the matter, is that accessibility is just as good as in the standard high chassis, and this in spite of the feet that the height to the top of the frame is only 1 ft. S ins, when the body is in position. To make a proper comparison between the two types of chassis we had them placed side by side, and found by measurement that it is only the frame which had been dropped, the

units remaining in identically the same positions on the low chassis as in the high, so far as their clearance from the ground is concerned.

Every part except the Wheels can be removed without jacking up the vehicle, also without the use of a. pit, and this with the smallest tyres which can be used on buses, i.e., 32 ins. by 6 ins. Every effort is being made to meet the requirements of the user, and for this purpose either a double-reduction axle of the bevel-and-spur type or a banjo axle with underneath, worm gear can he provided; also there are two forms cif brake equipment, a transmission brake with the drum on the rear .MI(1 of the forward portion of the propeller shaft and wide brake shoes expanding in drums on the rear wheels, or sideby-side shoes in the rear wheels and no transmission brake. In connection with the side-by-side shoes. it may be mentioned that the inner shoes have liners fin. thicker, and the drum diameter is increased at this point to correspond. As a result of this arrangement a wheel can be withdrawn after considerable wear without the need for slacking off the adjustment of the outer brakes through ridging of the drum.

Front-wheel brakes of the PerrotBendix three-shoe type giving a servo effect and the Deviandre vacuum servo device are auoitional equipment, but are strongly recommended, for whilst braking on all wheels increases the frictional area, and, consequently, the life of the brakes, it does not, in the case of a heavy vehicle, have much effect in respect of braking power unless the strength Of the driver be supplemented. It is notable thatwhere 36-in. by 6-in. or 38-in. by 7-in, pneumatic tyres are employed instead of 32 ins. by 6 ins., the brake drums are made 4 ins, greater in diameter.

With the front-brake equipment, the front and one set of rear brakes are interconnected. If a transmission brake be employed this is operated by hand. The front and rear brakes are compen-, sated together, but whilst separate compensation is provided for those at the rear, this is not so in the case of the front brakes. , One of the advantages of the Dewandre servo system, which, incidentally, has been used for 12 months and has been found perfectly satisfactory, is that, in the event of a broken connection or of leakage, the brake is still operable by the driver.

There is a reason for the optional worm and double-reduction rear axle. The makers state that the doublereduction type is undoubtedly more efficient than the worm gear at slow speeds and with heavy loads, but on the level and at higher speeds there is no difference between them. We learned that on steep hills a heavily laden vehicle is nearly a gear better off with the

double-reduction type. This axle is, however, not quite' so silent as the worm type, and to keep it reasonably so it requires adjustment from time to time ;

therefore, the maintenance charges are slightly. higher.

To obtain access to the worm gear it is merely necessary to lift a trap in the floor and to remove the pressed-steel cover over the horizontal banjo. To remove the gear altogether it is only necessary to draw out the driving hub caps, each of which is secured by eight bolts, and if tight can be forced off by inserting two setscrews in holes proNide& The worm wheel and differential can then be taken out by removing the four nuts from the securing caps.

As regards the worm, it is only necessary to undo the rear cardan joint and four nuts from the end-plate housing, when the worm can be withdrawn complete without altering the adjustment of the bearings. As an alternative, the whole of the worm-gear housing, with the differential, etc., can be dropped out by removing ten nuts, this, of course, being after the axle shafts have been withdrawn. It was proved to our satisfaction that the worm gear can be exposed for inspection in four minutes.

With 32-in. by 6-in. tyres the backaxle clearance in, the case of the worm type is 5i ins, and for the doublereduction type n ins. The chassis, of course, is built to meet the latest requirements, "10 ins, clearance being

provided up to the back axle. • The latest model chassis—and, inci-_ dentally, the others—have a neat device in the petrol tank which affords a reserve supply of two gallons. There are two suction pipes with a tap between them, both of which communicate with a pipe leading to the Autovac. One pipe reaches to the bottom of the tank, whilst the other is shorter. Normally, the tap between them is open, and when the level of the petrol is reduced "to below the shorter pipe, only air is sucked until the tap is closed, when the remainder of the petrol is used.' A feature of -the device is that the lever operating the tap prevents the removal of the filler cap of the tank until it is returned to the normal position.

The engine has its cylinders arranged in three pairs with individual detachable heads, whilst the exhaust manifold is in two sets of three pipes which converge to the centre. Around one of the manifolds is a hot-air muff for the carburetter, and communicating with the muff is a small pipe which brings oil vapour from the crankcase to assist in lubricating the sleeves. There is a cross-shaft at the front, the off-side end of which drives an eketric generator, above which, and driven by .a silent' chain, is a B.T.H. magneto. One distributor is employed for both magneto and coil ignitions, this being driven from the eccentric shaft and brought at an angle from the near side of the crankcase. A silent chain drives the eceenIzic shaft from the rear. of. the crankshaft, a plate affording a means of inspection. The filler cover and level tap are combined, and with the sight-feed rod are situated at the

back of the engine. A. vibration damper is fitted at the front end of the crankshaft.

The clutch is-of the single-disc type, with one friction ring on the disc and the other on the pressure plate. There are three toggle levers with setscrew. adjusters, the inner ends working in ball sockets in the clutch-withdrawal sleeve. A three-ply fabric coupling is mounted on the clutch shaft and embodies a small drum for the clutch brake. Gearbox and engine are mounted on the Guy patent -flexible sub-frame, which is suspended by three universal joints from the main frame and totally

obviates distortion. A two-piece propeller shaft with three universal joints is employed.

The rear springs are underslung, thus giving practically vertical, axle movement. The springs are long and flat, and 'are automatically lubricated from the axle casing. Oil lubrication throughout the chassis has received the utmost consideration ; even the steering rods form oil reservoirs and have wick lubricaters.

The appearance of the whole chassis is greatly enhanced by the new-type radiator, which has a polished aluminium outer shell in one piece and a built-up tubular interior. Throughout the chassis there are indications that the greatest attention has been paid to even the minor parts of the design. Take, for instance, the back axle. Here, to prevent the possibility of spring in the housings and caps of the taper-roller differential bearings, the caps are extended to make contact with the sides of the banjo. The adjustment of the bearings is effected by ring nuts controlling the bearing sleeves, the rings being each locked by a setscrew passing through its respective bearing cap. The Worm is easily adjusted by brass shims.

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