THORNYCR IT AG
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FOLLOWING the success of their Trusty eight-wheeler, Transport Equipment (Thornycroft), Ltd., Basingstoke, . . have now applied the same formula to a new ' maximum-capacity solo four-wheeler—the Mastiff. . The advantages of employing a " home-made " engine and gearbox in such a vehicle are obvious when considering the results obtained on test with this chassis, the vehicle having a maximum speed of more than 53 m.p.h., yet averaging 14.4 m.p.g. fully laden and 20 m.p.g. unladen over a
particularly traffic-filled and undulating route.
Because it has been designed for operation at 14 tons gross, and because this is the maximum legal rating for a four-wheeler in Great Britain, it has been possible to build in a big reserve of strength and power. The Mastiff should continue to deliver its highly commendable performance for many years when lighter, overladen four-wheeled chassis have been consigned to the scrap heap. This is a long-term economy plan still appreciated by many. operators.
• First-class performance does not end at fuel consumption and maximum speed. Acceleration is at least as good as that of many vehicles running 4-5 tons lighter; hill-climbing performance gives a gradient ability of 1 in 4.6; the brakes give safe maximum retardation and anti-fade properties, and the cab comfort (particularly in respect of space and quietness) sets a high standard.
The Mastiff is available in two wheelbases---16 ft. 6 in. (as testect).and 12 ft 6 in. (a tipper). . The dry chassis weights of these two models are 4 tons and 3 tons 174 cwt. respectively, whilst the standard plastics cab weighs 5+ cwt. and spare wheel and other equipment add a further 6 cwt. . Thus the long-wheelbase model has a body-and-payload rating of 9 Ions 8-1 cwt., whilst that of the short-wheelbase version is 9 tons 111 cwt.
A new six-cylindered direct-injection engine—the Thornycroft NS6—is employed, it has a bore of 104.8 mat. and stroke of 152.4 mm. (7.88 litres). This is the same capacity as that of the NR6/MV unit from, which the.NS6 engine is developed, but whereas the earlier
unit had peak outputs of 100 and 335 lb.-ft. torque, the NS6 has net outputs of 109.b.h.p. and 354 lb.-ft. torque, whilst the specific fuel Consumption is 0.355 pt./b.h.p./hr., which is slightly less than that of the .NR6/MV.
• The unit has a combined crankcase and .cylinder-block casting and twin cylinder heads. The nitrided crankshaft runs in seven thin-shell, steel-backed, copper-lead-lined main bearings and the C.A.V. fuel-injection pump has a mechanical governor. Multi-hole injectors are employed and fuel is passed through a brass-disc primary filter and twin paper-element main filters. The cooling system is 'pressurized to 4 p.s.i. and an oil-bath air cleaner is employed.
A 14-in.-diameter single-dry-plate clutch, with ballbearing release, is used and a new five-speed gearbox, similar in basic principle to the assembly used in the Trusty PK eight-wheeler, is unit-mounted with the engine. The box has constant-mesh gears with dog engagement and an Overdrive ratio of 0.81 to 1 can be added. This was fitted to the test vehicle and undoubtedly contributed towards the exceptional fuel economy. With thedirect-top gearbox the maximum road speed is 43 m.p.h.
A three-point flexible mounting is employed for the engine-gearbox unit. A two-piece propeller shaft with --flexibly mounted centre bearingtransmits the torque to the spiral-bevel rear axle. The standard axle ratio is .5.375, to 1, but for operation in very hilly areas or for tipper Use a 6.14-to-1 final drive is available. The front axle is based on an 1-section beam and the king-pins are carried in renewable bushes, with phosphor-bronze thrust washers.
Single-rate semi-elliptic. springs are used at both axles. The leaves are 31 in. wide in both cases and the lengths of the front.and rear springs are 46 in. and 60 in. respectively.
Girling two-leading-shoe hydraulic brakeswork in conjunction -with a Clayton Dew.andre air-hydraulic actuator coptrolled by an El valve. The single-pull hand brake gives exceptional leverage 'and corresponding efficiency on the road.
The Marles cam-and-double-roller steering:has a ratio of 28.5 to 1. A Clayton Dewandre continuous-flow hydraulic servo is offered as an optional eitra, one being carried by the test .vahicle. The short-wheelbase Ma-stiff has a turning
circle of 52 ft., that of the long-wheelbase model being 65 ft.
The chassis frame has 7/32-in.-thick side members, 10i in. deep, with flanges 3 in wide, and the frame is braced by six pressed-steel bolted cross-members. A 24v. electrical system is employed with a 288W. dynamo, and the standard fuel tank holds 30 gal. The tyres are 10.00-20 in. (14-ply) mounted on B7.0 rims, and a spare wheel is standard.
The upper half of the plastics cab is not unlike that employed on the Trusty range. The base assembly is somewhat different, however, principally because the cab is farther forward relative to the front axle. It is large for this class of vehicle, so that there is ample leg and elbow room for both driver and passenger. The driving position is further enhanced by the use of a fully adjustable driving seat arid the usual telescopic steering column.
Well-equipped Cab
A two-piece windscreen, wide centre rear light, corner rear lights, swivelling front-quarter lights and full-drop door windows give good all-round vision. Ample •storage space is ensured by the provision of two pockets on the mate's 'side ahead of the seat, and one ahead of the seat and one behind it on the driving side. Twin electrically operated windscreen wipers, an interior light, two ashtrays, two coat hooks and fitted rubber floor mats are standard, whilst a fresh-air heater and demister is offered as an optional extra, as are Windtone horns. . As supplied for test the Mastiff chassis and cab had a kerb weight of 4 tons 11+ cwt. and a test body and concrete blocks totalling 9 tons 8+ cwt. had been added to bring the gross weight, less driver and passenger, to 14 tons exactly. Distribution between front and rear axles was in the correct proportion of 1 to 2.
A large test tank had been provided and a fuel-consumption run was made first from the western end of the Basingstoke by-pass to Black bushe Airport, along the A30 road. The distance was 14 miles and as anybody who has used this road c2ó will testify, a more .nerve-racking 14 miles it is difficult to find in this country-the road being undulating, extremely narrow and carrying a large amount of heavy traffic.
Despite two stops and being baulked on one bill, the outward run was completed at an average speed of 27 m.p.h. and dr,: fuel-consumption rate was 14.4 m.p.g. Later in the day the • return run was made under even worse conditions and, although the average speed was slightly higher, the fuel-consumption rate was almost identical. During both runs the Mastiff was driven at around 35 m.p.h. and overdrive was used extensively.
Next day the fuel-consumption tests were repeated with the weights removed, the Mastiff running at 5 tons 9+ cwt. gross. . During both journeys the overdrive ratio was used continuously.. As the figures in the data panel show, the average speed for • the total distance was little different from that when running laden, but the fuel-consumption rate was 20 m.p.g. Thus, operators unfortunate enough to have to run their vehicles unladen on return journeys can expect an overall average of more than 17 m.p.g.
Braking Above Average
Braking and acceleration tests were made along a level stretch of road bordering Blackbushe Airport and the braking figures obtained were much above average. There was evidence of a slight amount of delay in the air-pressure system, but nevertheless the retardation from both 20 m.p.h. and 30 m.p.h.' was entirely satisfactory. Hand-brake efficiency was exceptionally high, the average Tapley meter reading of 42.5 per cent. being obtained without undue effort from 20 m.p.h.
Creditable acceleration times were obtained through the gears. using second, third, fourth and fifth ratios, whilst the directdrive figures were much better than are usually obtained from a vehicle running at this weight. Slight transmission rattle was observed between 13 m.p.h. and 18 m.p.h.
Farleigh Hill, which is 1.4 miles long and has an average gradient of 1 in 27, was used for the hill-climb and brake-fade tests, these being made in an ambient temperature of 72° F. At the start of the climb the radiator header-tank temperature was ISO' F. and the climb was made in 41 minutes, producing a temperature rise of only 8° F. The lowest gear used during the ascent was second, which was engaged for 1 minute 25 seconds, and the minimum speed was 6.5 m.p.h.
Two fade tests were made and, for each one, the hill was descended in neutral with the brakes applied to restrict the speed to 20 m.p.h., although towards the bottom of the hill top gear was engaged and full throttle applied to give the brakes something to work against on the reduced gradient. Both tests lasted just under 3+ rilintiteS, and after .the first descent a "crash" stop from 20 m.p.h. gave a Tapley meter reading of 69 per cent., showing that almost negligible fade had occurred. After the second descent-58 per cent. was achieved, this being equivalent to a reduction of only 0.1g. Thus the Mastiff was demonstrated to be almost fade-free.
Returning to the steepest section of Farleigh Hill, where the gradient is 1 in 8.4, the chassis was stopped and the hand brake held it with ease. Several smooth bottom-gear restarts were then made, although an attempt to restart in second gear was unsuccessful.
To anyone riding in the cab, an outstanding feature is the quietness of the engine, noise from which is little more than that heard by passengers in the upper saloon of a doubledeck bus. The test vehicle had a quilted bonnet cover, this being an optional extra, but some distance was driven with the cover off and even then the noise was appreciably less than would be expected from an engine of nearly 8 litres.
First-rate Gear Change •
Another outstanding characteristic is the gear change. This is so light and positive that it is a simple .matter to make upward or. downward changes without using the clutch, not that this is heavy to operate. Any gear change can be made quickly: thus, the new gearbox offers all the advantages of a synchromesh unit without the disadvantage of a heavy change because of baulking action.
The power steering fitted to the test vehicle made the Mastiff as light to handle as any private car, but without any loss of senSitivity.•arid the chassis cornered well at any speed. The suspension also was good, whether laden or unladen. Although operated by a treadle pedal, the brakes were not over sensitive,. but even better control would be obtained when running unladen were a conventional brake pedal to be employed.
Although the behaviour of the Mastiff on the road was above criticism, two small points relating to the cab require attention. They art the position and type of the combined grab handle and door pull, and the restriction of the door opening to about 80°. If the grab handles on the doors were to be placed across the front corner and were larger, it would he of greater assistance when entering the cab, whilst access for bulky drivers would be simplified if the door could be opened a little farther.
In the matter of maintenance the Mastiff also reaches a high standard. The first task was to check the radiator water level; this was done visually in 16 seconds, an external filler being employed. The engine dipstick can be reached only by removing the lower left-hand bonnet panel, an operation which becomes somewhat involved when a quilt is fitted. With the quilt on the oil level took 2 minutes to check and with the quilt off, 1 minute.
I spent 1 minute 25 seconds verifying the gearbox oil level, but afterwards found that the combined filler and level plug had the wrong size of head and that production boxes will have a small square-headed plug which will be easier to remove. This type of plug is fitted in the rear axle and enabled me to check the level in half a minute.
The brake-fluid reservoir is inside the cab, behind the driving seat, and the level was tested in 22 seconds, following which I checked the electrolyte levels in the four 6v. batteries in 2 minutes 40 seconds. The batteries are protected by a wooden cover which is held in place by two wing nuts. A fuse wire was changed in 1 minute 20,seconds, the combined control box, switch panel and fuse box being behind the driver's seat.
Injector Changes Easy
Turning my attention to the engine. I removed the quilt in 50 seconds and the plastics cowl top in 16 seconds. This done, the air-cleaner level was checked in 42 seconds and the fluid level in the power-steering reservoir in 14 seconds. The two main fuel-filters are attached to the upper left bonnet panel, where they are both easy to reach, enabling me to remove and replace the elements in a total time of 3f minutes.
I then removed an injector in 1 minute 55 seconds, choosing No. 1 injector, as this is, if anything, slightly more difficult to reach thanthe others. It Wag replaced in 1 minute 35 seconds and neither operation presented any difficulty. As has been shown in previous Thornyeroff tests, the brass-disc primary
filter can be stripped and reassembled in about minutes, Bleeding the fuel system at the .pump took 11 minutes, slight difficulty being experienced in seeing the outlet of the bleed pipe from above.
Engine tasks completed, thecowl top, which is secured by four large spring clips, was replace. d in 40 seconds and the quilt in 1 minute 20 seconds. It is possible to work on the engine while sitting in the cab without feeling in any way cramped (a further advantage of a wide cab), whilst there is plenty of room around the sides of the power unit. The lower left panel gives good access to the fuel-injection pump and air compressor.
Simple Brake Adjustment
By jacking up centrally under each axle I was able to adjust the front brakes in 11 minutes and the rear brakes in 2 minutes. Each brake has only one square-headed adjuster, and the total time taken was much less than is usually needed for much lighter vehicles.
Saving the heaviest job until last, I managed, single-handed, to remove the spare wheel in 11 minutes, but needed assistance to replace it in 21 minutes. The wheel is secured on its carrier by two eared nuts, but a 10.00-20-in. wheel and tyre are no light weight and I would have thought that a Winch carrier, as used on the Trusty, would have been a likely fitting for the Mastiff, which has larger tyres than an eight-wheeler.
All these maintenance tasks were carried out with the standard tool kit, which, as usual with Thornyeroft vehicles, is complete. It includes oil and grease guns, an oil can, feeler gauges and two spare bulbs for the optional flashing indicators..