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Good Braking, Acceleration . and Fuel Consumption Yielded by Chassis

10th December 1948
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Page 44, 10th December 1948 — Good Braking, Acceleration . and Fuel Consumption Yielded by Chassis
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with 10.35 litre Engine, Fluid Coupling and Preselective Epicyclic Gearbox IN the description of the latest addition to the Guy Arab passenger range, published first in `! The Commercial Motor" on September 10, stress was laid on the ample power available from the Meadows-Guy p.s.v. 1035-litre oil engine, and it was stated that the chassis would be available with a fluid drive and pre-selective gearbox. At that time, prototypes had covered great mileages and plans for production had already been made.

To obtain an unbiased opinion on the performance

of the vehicle, the manufacturer offered one of the first production models for my test. During its trials, no fault was found with the performance, accessibility or driving comfort, and I was left with the impression that its ample reserve of power and generally robust cogstruction should extend the normal periods between maintenance. Moreover, the accessibility of all components should materially reduce the number of manhours required in upkeep. The performance is well within the standard set up by chassis designed since the war, and, with the air-operated pre-selective gearbox, drivirig fatigue is greatly diminished. • As an example of the reserve power, 'the engine is deiated to develop 115 b.h.p. at 1,800 r.p.m., which is • irs'nominal Setting controlled by the fuel-injection pump. In effect, this setting reduces loading on the pistons, connecting rods, crankshaft and bearings, and should increase the potential life of these components.

• Compact Power Unit Although of large capacity, the power unit is comparatively compact, and is fitted into the original Arab frame without need for moving the cross-members. Crankshaft bearings as wide as possible, consistent with the length of the power unit, are employed, and are of large diameter to provide the requisite surface area. The connecting rods are of such diameter that they are split obliquely at the big-end to facilitate removal through the cylinder bores. Providing rigidity and freedom from stresses, the cylinder block and crankcase form a monobloc casting of high-grade cast iron, the cylinder bores being fitted " with renewable dry liners. Two interchangeable cylinder heads, each covering three bores, are made from the same material, and are equipped with replaceable valveseat inserts. The connecting rods are of a sturdy H-section, fitted with steel-backed thin-shell precision-finish big-end bearings, the caps being secured to the rods with, four bolts. The gudgeon-pin bushes are pressure-lubricated from the big-ends, through drilled passageways in the webs of the connecting rods. Hardened fully floating gudgeon pins of 1s-in. diameter, are located end-wise by means of circlips. A feature of the engiqe is that the main casting may be turned end for end, and the components arranged on either side for leftor right-hand control. On the test chassis, a home model, the air manifold, fitted to the left-hand side of the engine, was equipped with two heavy-duty oil-bath air cleaners. These cleaners also proved effective as air silencers, because there was no noticeable induction roar during the test.


The Guy fluid coupling is of conventional interior design, hut of large capacity to meet the heavy demands of short-stage operation. With the-filler plug at an angle of 37 degrees from the vertical, it has a capacity for 26 pints of oil, the recommended uantity. In the construction of the Wilson gearbox, manufactured throughout by Guy Motors, Ltd., provision has been made for .fitting an additional train of gears if required, thus providing for fouror five-speed gearboxes with over, or under-drive. It has arrangements for driving an electrical or mechanical speedometer, and a further drive is available for operating an automatic chassis lubricator. ' The test chassis was equipped with an R.P. automatic lubricator, actuated, by compressed air and connected to the gearbox air-supply system. The air equipment included a reciprocating compressor, driven from the front propeller shaft, an internal cylinder in the gearbox, which operated the bus bar, and brake cylinders at each wheel. The front air cylinders were secured to the tops of the stub axles, whilst those at 1116 rear were attached to a cross-member. The frame, axles, steering gear and suspension are basically the same as those employed on the earlier Arab chassis, slight modification having been made to the frame cross-members to accommodate the preselective gearbox.

Light Steering After weighing the chassis in unladen form, the representative load for the body and full complement of passengers was secured amidships on the frame. Unfortunately, a container for the rear ballast weight was not available, and the full load had to be accommodated in the centre of the chassis. This caused uneven weight distribution, and I discovered that approximately 45 per cent. of the running weight was being carried by the front axle. This could have produced stiff steering, but I was surprised to find that control appeared to be no heavier than on some vehicles of other makes. With correct weight distribution, the steering should be exceptionally, light_

Leaving the works at Wolverhampton, a course was steered towards Cannock, to reach a level stretch of road on the Watling Street for acceleration and braking tests. Driving in a normal manner, without abuse of the gearbox, the Arab was accelerated from rest to 20 m.p.h. in 12 secs.. and 30 m.p.h. was reached in 23.5 secs. The latter time was improved on the return run, and an average of the times of two trials in each direction showed that 30 m.p.h. could be reached in 23.1 secs.

The Arab is thus up to the standard demanded of large-engined modern passenger vehicles. In an attempt to better these figures, I abused the gearbox in a manner generally known only to certain bus drivers. Apart from moving away from rest with a jerk, the remainder of the gear changes, although rapid, were accomplished with a smooth take-up by the transmission. This trial showed a reduction of 1 sec. on the previous test.

Because of the uneven weight distribution and wet road surface, the conditions for brake testing were far from ideal, and I was prepared for complete rear-wheel locking. Nevertheless, on the first emergency stop from 30 m.p.h., the chassis maintained a straight course, and although the path of the rear wheels showed heavy marks, they had locked for only 2-3 ft. before coming to rest. The retardation was progressive and without unpleasant suspension bounce when the chassis finally halted.

The Arab could be brought to rest from 20 m.p.h. c10 in 16 ft., and from 30 m.p.h. in 40 ft. These figures are adequate for a passenger vehicle, because a higher rate of retardation would cause discomfort to standing passengers. In subsequent driving of the vehicle, I found that the brakes could be used progressively to obtain smooth retardation from any given speed. There was no lack of delicacy in the " feel " of the brake nor the slightest suggestion of delay in its functioning.

After these trials, we adjourned to Cold Hill, Tattenhall. On reaching the foot of the hill, I doubted whether the machine would be able to start from rest at the steepest point. First, I drove to the top of the incline, a distance of about 300 yds. The first part was not severe, but towards the top, the Tapley gradient meter recorded a section of 1 in 5.

This I considered would be an ideal test for the transmission, as well as the engine. First, the brakes were tested, and it was found possible to hold the vehicle on the hand brake alone. Engaging low gear, I released the hand brake and accelerated to the full. To my surprise, the Arab pulled smoothly away from rest without sign of hesitation. I reversed to the starting point, checked the gradient, and tried again, with the same result. After photographs had been taken, a third attempt was made from the same spot, and with the same results.

The vehicle was then driven to Watling Street for consumption trials. Unfortunately, the -return circuit

from the fuel pump prevented the use of my standard measure, and an auxiliary system was rigged up along

side the fuel tank. this tank was filled to a predetermined level, and connected into the injection-pump supply. On the first run, it was discovered that an air lock had entered the supply when changing the pipes, and the test was abandoned after a few miles. Returning to our starting point, the system was primed until all air had escaped, and after refilling the test tank. the run was resumed.

Average of 29.4 m.p.h.

A circuit of 12 miles was made, so that we returned to our starting point. It included normal main-road gradients and two roundabouts. The first trip was made without stop, and except for slowing down at corners, a steady speed of 30 m.p.h. was maintained. The average speed for the course was 29.4 m.p.h., the fuel consumption being equivalent to 12.8 m.p.g.

A second circuit was made with four stops to every mile, representative of service conditions for a doubledeck bus. The Arab was not spared on this test, for the brakes were applied fiercely at every stop, and it was accelerated as rapidly as possible. Moreover, I took every opportunity of starting on gradients wherever they were to be found. While on this test, I checked the atmospheric temperature, which was 63 degrees F., and the radiator temperature, which remained fairly constant at 159 degrees F., showing there would be no likelihood of boiling under hot summer conditions.

At the end of this course, calculations revealed that the fuel-consumption rate was precisely 8 m.p.g., and deducting the 15-sec. stops, our average running speed was 22.9 m.p.h. This proves that the Arab has ample power for fast schedules without waste of fuel.

Temperature Readings Before starting this test, I had taken the temperature of the oil in the fluid coupling, 120 degrees F. being recorded. At the end of this course, the temperature had reached 176 degrees F. Had the coupling been of smaller capacity, the temperature might have been considerably higher. Other temperatures recorded at the end of the test were: engine lubricating oil, 142 degrees F.; gearbox, 132 degrees F.; and rear axle, 155 degrees F.

On the eight-mile return journey to the works, a high average was maintained, and for long periods our speed was 40 m.p.h. The vehicle was stable and, with the good braking system, it was completely under control at all times. The total distance for the day was 60 miles.


Locations: Wolverhampton

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