BRISTOL
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Introduces a
DOUBLE-DECK Bus FOR a considerable time now the Bristol Tramways and Carriage Co., Ltd., Brislington, Bristol, has been busy with the design, production and road testing of a new four-wheeled Chassis for double-deck buses. The company's 114 b.h.p. six-cylindered engine has proved admirably successful in the fl-type single-decker chassis, and has all the power, smoothness and flexibility needed for double-decker duty. Naturally, therefore, it has been adopted as it stands, and, with it, all of the features of the lighter chassis which were applicable—notably the variable-length springs, the separate rubber-mounted gearbox, offset transmission line, and Merles steering. The layout is as simple as possible, and evidence of the company's long operating experience appears in the regard paid to the maintenance engineer.
The wheelbase of this G-type doubledecker chassis is 16 ft., permitting conveniently an overall vehicle length of '26 ft. The frame is upswept and arched in orthodox manner, giving a laden height of 1 ft. n ins. amidships
and 111 ins, behind the rear wheels. At the rear arch the members are reinforced by welded plates, and their maximum section is 11 ins. by 33 ins. by 7-32-in., the overall frame width being 3 ft. 9 ins. Pressed-Steel cross-members are used, together with two 43-in. tubes which are opposite the two ends of the rear springs.
The well-known six-cylindered aidevalve engine has a bore of 105 mm. and a stroke of 140 mm. The upper part of the crankcase is now an Elektrou casting, the base chamber having been made of this metal for the past year or more. Another minor alteration which we noticed is the use of a triple instead of a double chain for theauxiliary drive. Otherwise this unit is in all respects similar to that fitted in the fl-type single-decker chassis, of which a road-test report appeared in our issue dated I)ecember 30th, 1930.
The same applies to the gearbox, which is carried on four rubber mouhtings between the near-side frame mathher and an intermediate longitudinal. There isa fabric coupling before the
gearbox, and the propeller shaft carries two Spicer mechanical universal joints.
The final drive is by David Brown 7.6-to-1 underslung worm with six-pinion parallel-type differential gear to fully floating nickelchronae axle shafts, the whole contained in a IGrkstall case which is a one-piece nickel-chrome forging. Marks steering gear is retained, and its action rendered lighter by the use of tapered-roller bearings in the stub-axle king-pins. The brake equipment is novel and will be of interest to municipal and other operators • more is likely to be heard before long of the system which the Bristol concern will exhibit for the first time at next month's Olympia Show. One pair of shoes, 71 ins, wide, in each of the 17/-in, rear drums is operated by both pedal and hand lever. The foot brake operates through a 1 hawandre vacuum cylinder on the outer face of the off-side frame member, this being coupled to a pair of cylinders on the inside of the frame members. The master cylinder operates the rear brakes, whilst the two smaller cylinders, acting through rods, pull on their respective front brakes. Compensation is obtained between front and rear, and between the two front brakes, 'and time lag is eliminated by using a short copper pipe of 1-in. internal diameter from the induction manifold to the master valve. A separate crossshaft is provided for the hand brake, each rod pulling on a common cam lever . with the corresponding foot-brake rod. Both foot-brake and hand-brake erossshafts are carried in spherically housed
• ball races.
The reverse-camber springs, 43 wide, take the load from the frame through cams which hare the effect ot shortening the spring length as the load is increased—the familiar Bristol fea
• tune. Both front and rear springs are anchored at their forward ends by eecen' trio bushes which, under varying conditions,preserve the longitudinal location of the axles. The rear ends of the springs slide' under theit cams and
• are enclosed at the _real as well as beneath. The standard tyre My._ is 36 ins. by ins. (twin rear), and the chassis weight, with water, oil, tools and spare wheel is 4 tons 5 cwt. The gear ratios are 7.6, 12.5, 21.0 and 41.1, to 1 for ward, and 29.1 to 1 reverse. The price has not yet been decided.
The Bristol B-type four-cylinder and D-type six-cylinder single-decker chassis (both of 16-ft. wheelbase) are still available, and corresponding models of 17-ft. 6-in. wheelbase, to be known as types H and J, are now introduced. They embody all the latest innovations which the company has adopted up to date, and are particularly interesting.
The J-type chassis has the 114 b.h.p. engine embodying the improvements referred to above. The H-type chassis has the 70 b.h.p engine of 44 ins. bore and 5t ins, stroke which figured in the original B-type machine, but one or two modifications have been made. The free-wheel dynamo drive is now by skew gear from the off-side chaindriven shaft from which the Simms magneto is driven, so that the dynamo is at the front instead of the rear end of the engine. The new position is not inconvenient, and it enables the gearlever bracket to be bolted direct to the crankcase, as well as permitting the batteries to be housed in a steel container forming the pedestal for the driver's seat. It is found that batteries receive better attention there than under the saloon floor.
An up-draught Clandel Hobson carburetter, with power jet, is now fitted beneath the exhaust manifold, the .lngoing mixture passing a hot spot before entering the centre of the internal' in.duction manifold. An Auto-Klean oil filter is now used, and the "oil radiator as fitted on the six-cylinder models is adopted also for the "four." As in the more powerful chassis, the water radiator is mounted by two rubbersleeved clips on the detachable tubular front member and is positioned by a rod from tbe engine block. The original three-point engine mounting, the front end hanging from a bridge, is retained.
The clutch now has a neater automatic lock on each of the three togglefulcrum adjusters.
Whilst the gears, shafts and bearings of the gearbox are unaltered the selector forks and case have been modified to place the side-mounted control rod in line with the gear-lever bracket qn the side of the engine. The gearbox is now carried in a sub-franie on two longrubber pads, . these extending: its full length on each side. As Simms Juriel couplings are used before -and behind the box the unit is virtually rubber-insaluted.
Despite the increased wheelbase tin) standard tubular propeller shaft is -employed, although it now has Spicer universal couplings. Between the gearbox and this tube a short shaft conveys the drive to an intermediate doublerow rigid ball race, and for alignment this is simply carried in a thick rubber sleeve (cylindrical inside, spherical outside) with a stout Elektron casting bolted to a cross-member.
The rear axle is exactly as on the double-decker except that ratios of 5.4 or 6.5 are available, The former gives overall gears of 5.4, 8.8, 14.8 and 29,0 to 1 forward and 20.5 to 1 reverse, and the latter 6.5, 10.7, 17.9 and 35.0 to 1 forward and 24.7 to 1 reverse.
The use of common brake shoes, cams, spindles and cam levers for foot and hand operation of the rear brakes is, a feature of the 32-passenger chassis, but the latest Dewandre practice is followed of mounting the front-brake cylinders on the stub-axle top plates.
The frame of the two new singledecker chassis is lower and, to eater for its extra length, deeper, its maximum section being 10 ins. by 3§ ins. by 7-32 in., whilst the width is 3 ft. 10 ins. and the laden height 1 ft. 9 ins. The members of the gearbox sub-frame give vertical rigidity to the deep longitudinal%
For both new single-deckers 38-in. 14 9.00-in, low-pressure tyres (twin rear), are standardised. The H-type fourcylinder chassis weighs 3 toms 15 cwt., and the J-type " six " 4 cwt. more. The price of neither has yet been settled.