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A Vehicle Buili 'or Hard Service

9th April 1948, Page 38
9th April 1948
Page 38
Page 39
Page 40
Page 38, 9th April 1948 — A Vehicle Buili 'or Hard Service
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THE designer of the Vulcan 6-tonner obviously set out to produce a vehicle that would withstand arduous service with a minimum of attention. He accordingly laid out a well-proportioned frame having five deep-section crossmembers bolted in position, and specified sturdy transmission units. To enable essential maintenance to be carried out expeditiously, he arranged that the engine and other parts of the vehicle should be easily accessible and that the brakes should be readily adjustable.

During "The Commercial Motor" road test two adjustments were made to the brakes. These were completed almost before I had time to realize that the fitter had started them.

Engine accessibility is outstanding. The long bonnet sides and top, secured by spring-catch fasteners, can be removed to expose the full length of the power unit from the fan to the -clutch housing. In addition, the near-side wing can be withdrawn by unscrewing five nuts, and the passenger's seat can be taken out by removing a single bolt.

By these means, the engine and its component parts are exposed from frame level upwards and the fitter can stand between the road wheel and the frame to work in comfort.

The Vulcan 6 P.F. chassis employs the Perkins Mark III N. engine, which is mounted in the frame at three points, with a sandwich pad at the front and Silentbloc bushes at the rear. This engine, of precombustion chamber pattern, is equipped with Ki-gass equipment, which is used for starting under exceptionally cold conditions. Bolted to the rear of the engine to form a unit, the four-speed gearbox has a constant-mesh third gear, which is engaged by sliding-dog operation.

The short-wheelbase model which was tested was equipped with a single-piece propeller shaft fitted with Hardy-Spicer needle-rollerbearing joints. This shaft conveys the transmission to the heavy-duty overhead-worm drive of the fully floating axle. The chassis had a 7.75 to 1 final drive, which is an alternative to the 6.5-to-1 ratio available throughout the range of models_ In keeping with the robust design of the chassis, the differential gear incorporates a four-pin. bevel and the driving shafts are machined from nickel chromium steel. A Clayton Dewandre servo and Lockheed system operate through Girling two-leading shoes on all wheels.

With the 9-ft. 9-in.-wheelbase chassis there is limited room between the hand-brake lever and the fuel tank on the off side of the chassis to house the servo unit, which is arranged to slope down to the fore end, thus avoiding sharp bends in the pipe line. The vacuum tank is housed inside the frame immediately behind the gearbox.

Light steering action is achieved through the use of Marks cam-anddouble-row gear and a large-diameter spring steering wheel. The instruments are grouped on a panel mounted on the steering column and the batteries are housed in an accessible position under the driver's seat.

The chassis selected for the test was fitted with a cab and is suitable for use with a 5-cubic-yd. tipping body or a 1,000-gallon tank. Running weight was checked on the manufacturer's weighbridge, and with driver, observers, tools and spare wheel, the gross weight was 9 tons 21 cwt. This allows for a body and 6-ton payload, which is well catered for by the 36-in. by 8-in. tyres.

Starting the test from the Maidstone works, we passed through the town and travelled towards Ashford . in search of a suitable gradient for the hill-climb. Kent is noted for hills and within a few miles of leaving the works we reached Hollingbourne Hill. This presented a mile climb of 1 in 14 average gradient with a section of 1 in 6, where a stop-start test was made.

After taking the atmospheric temperature (47 degrees F.) and the radiator temperature (146 degrees F.) at the foot of the hill, we began the test: With a gradient of 1 in 32 showing on the meter, we started from rest in second gear, which was held until a gradient of 1 in 8 was reached, where the failing engine speed enforced a change to bottom gear. .The remaining 400 yds. of the climb were covered at 5 m.p.h., which was governed engine speed in low gear.

With the lower portion of the radiator screened, I had expected to find a high temperature rise, but it a6 had increased by only 23 degrees F. to 169 degrees F. The large-capacity radiator, which is standard on both home and overseas models, and engine efficiency were responsible for this resistance to overheating.

On the second climb the stop-start test was accomplished without difficulty, the low final-drive ratio of 7.75 to 1 playing its part in this achievement. On the Second descent of the hill the brakes were used to keep the speed to 30 m.p.h., and an emergency application at the foot of the hill proved that their power had not been decreased by a high temperature.

As the chassis had been collected from the production test bay the brakes had not settled down, and the initial test locked one of the rear wheels. In less than a minute the opposite brake had been adjusted and we were ready to continue the tests. These showed a high standard of efficiency which, because of the servo action, is attained with light pedal pressure. From 30 m.p.h. we came to rest in 41 ft., equivalent to 73 per cent. efficiency, and from 20 m.p.h. in 19 ft., or 72 per cent. efficiency.

Difficulty was experienced in locating suitable ground for acceleration tests, and when a level stretch was found we had to contend with a strong headwind, which caused up to 12 secs. variation of results in each direction. With no other suitable' road in the area, I was forced to make the tests under this rather unsatisfactory condition. Starting from rest and using the gears, 20 m.p.h. was reached in an average of 20.6 secs. and 30 m.p.h. in 44.1 secs. Top-gear acceleration, which was more affected by the headwind, showed that 20 m.p.h. could bc reached from 10 m.p.h. in 20.7 secs and 30 m.p.h. in 44.9 secs.

The fuel-consumption test was made on a 20-mile out-and-return course on the Maidstone-Ashford road, which 'included several sharp gradients where third and second gears had to be used.

' It was at this stage that I noted the comfort of the coachbuilt cab, which has a multi-strut roof, serving a dual purpose of providing rigidity in construction and effectively dampening any tendency to reflect engine noise or cause drumming. Ample ventilation is provided by both front screens, which are adjusted by sectors, a roof ventilator and sliding side-windows. Visibility is excellent, all controls are conveniently placed and the driving position affords maximum comfort.

From the results of the test it was ascertained that 14.2 m.p.g. had been recorded at an average speed of 26 m.p.h. This is a reasonable result, considering the high average speed, coupled with the low-ratio final drive, which requires more engine revolutions per mile than the 6.5-to-1 alternative ratio. Vulcan vehicles with the higher-ratio axle should attain 16 m.p.g.

To test the versatility of the vehicle on a more strenuous course, the Vulcan was taken over a second consumption test, which included Wrotham Hill, •a steady mile climb which enforces considerable use of low gears. On this test the low axle ratio proved an advantage, and a consumption of 13.78 m.p.g. was recorded at a relatively high average speed. With such little variation in consumption, this model will provide economical running in hilly territory.


Organisations: Hard Service

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