ANOTHER LIGHT LOW PASSENGER CH A SSIS.
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The Latest Bristol Product for 32-seater Buses having a Floor H ight of 26 ins, and a Laden Weight of 5i Tons.
T AST October, when dealing with the _L./passenger-vehicle programme of the Bristol Tramways and Carriage Co., Ltd., we described in detail the lowbuilt chassis for buses seating up to 60 persons and, at the same time, pointed out that a much lighter chassis with a low frame level would be placed on the market some time later to meet the need for single-deck buses seating up to 32 persons.
We are now able briefly to describe this new chassis which is known as the Bristol Type B, the first having been ordered by the Corporation of Chesterfield.
It has been built• throughout to meet the recommendations of the Ministry of Transport, thus a complete bus of the 30-seater type and laden with passengers weighs approximately 51 tons, whilst the unladen weight of the chassis is 2 tons 14 cwt. The other main chassis dimensions are : overall length, 25 ft.; length behind driver's seat, 20 ft.; overall width, 7 ft.; wheelbase, 15 ft. 7 ins.; track (front), 6 ft. 1 in., (rear) 5 ft. 81 ins.; height of frame from ground, 25 ins.; height of body floor, 26 ins.; clearance up to 15 ft. from front of chassis, 101 ins.; diameter of turning circle, 58 ft. 6 ins.
Optional axle ratios of 51-1 and 64 can be provided, and on the various gear ratios the corresponding road speeds are: top, 1-1, 40 m.p.h. and 34 m.p.h.; third, 1.66-1, 22.5 m.p.h. and 20 m.p.h.; second, 3.125-1, 12.8 m.p.h. and 11 m.p.h.; first, 6.25-1, 6.4 m.p.h. and 5 m.p.h. ; reverse, 3.94-1, 10.1 m.p.h. and 9 m.p.h., these speeds being calculated with the engine running at 2,000 r.p.m.
The power unit is a four-cylinder monobloc of 41 ins, bore and 51 ins. stroke rated at 32.4 h.p., although actually developing 42 b.h.p. at 1,000 r.p.m. and 60 b.h.p. at 2,000 r.p.m.
The cylinder head casting is detachable, bnt the bayonet-socket valve caps permit the valves to be removed and replaced without detaching the heads.
As the engine is designed for comparatively high-speed work, aluminium pistons and Duralumin connecting rods are provided, whilst the crankshaft is a nickel-steel forging of 21 ins. diameter. The timing drive is by an adjustable silent chain, whilst the vertical dynamo and magneto are driven by spiral gearing and the cast-aluminium fan by a belt. Lubrication is effected by a submerged gear-type pump which supplies oil direct to the main bearings and to the troughs for the connecting-rod dippers. An oil strainer of large area ensures cleanliness and prevents choking.
Following Bristol practice, the cooling water is circulated thermo-siphonically through a gilled copper tube radiator with cast-aluminium tanks, this being mounted on springs to prevent racking.
A. dry-plate clutch with asbestosfabric friction material and self-locking adjustment conveys the drive to a fourspeed and reverse gearbox mounted on rubber shock absorbers, a somewhat novel method, but one which certainly has many points of merit. The box itself is an aluminium casting. All the shafts run on ball or roller bearings, whilst the gears have ground teeth to ensure silence. The Bristol patent control gear by one selector rod is employed. This type of control has been standard on Bristol vehicles for some years and has proved most successful.
Two fabric-disc joints are used for the tubular propeller shaft, which is 3 ins. in diameter. The final drive is by underslung worm mounted in a cast-steel axle casing into which are forced nickelchrome steel axle tubes. The differential is of the bevel pattern, and roller bearings are employed for the road wheels, which are of the disc type equipped with 34-in. by 7-in, straight-sided pneumatic tyres, singles at the front and twins at the rear, the air pressure for these being obtained from a mechanical pump driven off the e
The front axle is a nickel-chrome steel stamping especially designed for use
with front-wheel brakes. The front wheels themselves are ea ried on ball and roller bearings.
The brakes used are a and brake of the contracting type mo nted at the rear of the gearbox, and internal expanding shoes controlled by foot and _ acting on all four wheels, the internal diameter of the drums bein 171 ins. To assist the driver in the pplication of the foot brake, a Dewa dre vacuum servo device is incorporate. If desired, the front-wheel brakes can e omitted.
Three per cent. nickelel pressings form the frame, which, at its greatest, has a section of 8 ins. uy 21 ins, by lasi-in. Tubular cross-i embers are provided between the poi its of attachment of the rear-spring hr kets.
Springs automatically adjusting to load are utilized, these ieing on the Bristol system, by which e spring cen
tres shorten under load, he length of the rear springs is 5 ft. 9 ins, and of the front springs 3 ft. 1.01 ins., the width in each case being 3 ins.
Steering is effected th ough a hardened steel worm and q adrant controlled by an 18-in, hand vheel. Stops are utilized on the axle be to cheek the lock.
All the ball steering joints have pinned nuts and the balls e upright, so that they are protected fro dirt by the joint bodies.
To provide maximum ''ace for the passengers, the driver's as t is mounted beside the engine, the cha ge-speed and brake levers being at h s left hand, whilst the ignition and slow-running controls are carried on the , steering column.
Fuel up to 30 gallons i carried in a tank below the body on th -off side and attached by three mild-ste 1 straps; the filler is outside the body. Well away from this tank are the exh ust pipe and silencer, which are carrie on the near side. A small but importi it point from the safety aspect is that the hubcaps come inside the wheel r' s.