A THORNYCROFT FREIGHT HIICLE FOR 6*-TON LOADS.
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The Material Advantage of the For Dimensioning in Order to Obta asition for the Driver and of Careful daximum Useful-load Capacity.
TFW 7-ton Thornycroft freight chassis, which is known as the type CC, has now undergone its final testing at the hands of a few selected users and lain general production. It is designed to give the fullest possible loading capacity, whilst conforming with the maximum legal load limits operating in the United Kingdom, which are 12 tons for the total axle weight with a maximum of 8 tons for any one axle. The weight of the CC chassis is 4 tons 4 cwt., and, allowing for a body weight of from 20 cwt. to 21 cwt., a margin of 61 tons is left for the accommodation of the useful load. Where the total load limit is more than 12 tons, the vehicle is held to be capable of carrying 7 tons.
In order the better to distribute the load so that the full value of the capacity of the front axle can be obtained, the control position for the driver is placed beside the engine, the steering box being mounted upon the front dumb-iron. A seat for the driver's mate is provided on the left-hand side of the engine and in this way an available body space behind the driver's cab to the rear end of the frame of 18 ft. 1 in. is obtainable. The width over, the hubs of the rear wheels is 7 ft. 5i ins., so that the chassis can be fitted with a body of considerable capacity, whilst, at the same time, the wheelbase does not exceed 16 ft. The overhang of the frame behind the rear axle is 5 ft. Oa in.
The new CC. chassis is the larger brother of the new JJ chassis, which is designed for 5-ton loads 'and may be mounted on solid or pneumatic tyres. The CC
• chassis, however, is expressly designed to be equipped with solids and it is not supplied with pneumatic tyres, mainly because of the greater overall .width
which they would entail. The JJchassis has. its driving seat in the normal position behind the dash, as more of its rated load can be imposed _upon its rear wheels ; the CC chassis, however, is not supplied with the driving seat behind the dashboard, as otherwise the conformity with the legal requirements for axle weight would not be possible.
The power unit which has been adopted for both the J,..T and the CC chassis is the MB4, which has its four cylinders cast monobloe with two detachable heads, the cylinder sore being 41 ins, and the piston
stroke 6 ins. According to the R.A.C. rating the horse power is 36.1; the engine, however, will develop 50 h.p. at 1,000 r.p.m. and up to 60 h.p. at higher engine speeds. Ease of inspection and maintenance has vied with the need for efficiency in dominating the design. Every detail of the engine is completely accessible with the minimum disturbance of other parts. A crankshaft of large diameter carried on three long bearings is employed, the shaft being drilled for the supply of oil to the big endbearings. The oil pump is submerged in the oil in the base chamber and it is readily detach-.
oil liller is raised to carburetter level. A hinged cover on one side of the bonnet, when raised, discloses both the carburetter and the oil filling orifice, thus greatly facilitating attention to the carburetter and the replenishment of oil in the ,base chamber. The level of the oil in the crankcase is ascertainable by means of a dipper rod, a test tap being fitted to indicate the high level point of the oil.
The magneto is mounted on a platform on the crankcase, which is driven from the front end of the Crankshaft through gear wheels. Provision is made for interposing a generator between the driving gear and the magneto when an electric lighting and starting outfit is fitted.
Advancing and retardation of the ignition are effected automatically. A Zenith carburetter of a type which is suitable for the engine and which gives ,the highest degree of economy is fitted, the hot-spot induction manifold ensuring complete vaporization. The throttle is controlled by an accelecator pedal, a maximum setting for slow running being obtainable through a lever on the steering . column. A propeller-type pump is run in tandem with the cooling fan, the water being passed through a geared tube radiator. Tension of the fan belt is regulated by means of an adjustable flange on the driving pulley. The top and bottom 'vessels of the radiator are removable and new tubes can easily be fitted should the old ones become damaged.
For the transmission of power a dry, single-plate clutch is employed, faced with asbestos fabric. The driven member is light and the clutch stop being efficient, gear changing is rendered simple and speedy. The gearbox is unmated at the rear of the crankcase and gives four forward speeds and a reverse, the gear ratios being respectively 1 to 1,1.56 to 1, 2.75 to 1 and 5.13 to 1. The ratio of the worm gearing in the back axle is 10.66 to 1.
With 40-in. by 6-in. solid tyres and with an engine speed of 1,500 r.p.na., the speed of the vehicle on top gear is 161 m.p.h. and on third gear 101 m.p.h.; on second gear the speed would be 6 m.p.h. and on first gear 3i m.p.h.
The engine unit is carried on three points with rubber buffers interposed between the engine arms and the brackets on the frame. The rubber pads between the frame brackets and the engine bearers at the rear are 1 in. thick and are carried in two dished plates, whilst a rubber washer betweeh two dished plates is interposed between the securing bolts and the engine bearer.
The gear turret is carried somewhat forward of its normal position, with the gear gate bracket sloped, forward so that the gear lever is brought to a convenient position for the driver's left band. Six floor boards, held by butterfly nuts to a pair of T-angle bearers on each side of the engine (these bearers being equipped with studs to take the butterfly nuts), render access to each side of the engine quite easy, for the boards and bearers can be removed in a. few moments and the mechanic can stand between the mudguard and the back of the cab within easy and comfortable reach of any part that may require attention. The single-piece bonnet is held to the floorboards by the usual bonnet fasteners and, as we have already said, a small hinged cover gives access to the carburetter for flooding purposes, etc.
The power unit is readily removable from the chassis when it is required to be taken to a bench for overhaul and it is claimed that alignment between crankshaft and gearshaft can be best obtained by the adoption of this system of combining the Units and by conducting the• work upon the bench. From the
power unit the drive is taken through an intermediate shaft through a Spicer universal joint, the fabric joint not being favoured because of the high torque which has to be transmitted in a vehicle of this size. The rear end of the intermediate shaft is carried in a ball bearing which is supported in a flexible housing, this now being the general practice on Thornycroft vehicles that have an intermediate shaft. The transmission brake acts upon this shaft and is the Thornycroft speciality,, which consists of a single ring of steel 7 ins, wide and in. thick, lined with asbestos fabric, held at its central point (with means for adjusting ft concentrically with the brake drum) and pinched together by moving fingers operated through rods from the brake lever.
The propeller-shaft is tubular and has two enclosed, metallic universal couplings, one of them being telescopic. The power passes to an overhead worm gear and through floating differential shafts, the final drive to the rear wheels being through external dogs, the driving shaft being capable of being removed without taking the load off the axle.
The steering gear, as we have said, is fitted outside of the frame, just forward of the radiator and embraces a worm and complete wheel, giving four lives to the worm wheel. The turning circle of the vehicle is GO ft.
A useful attachment for the rear wheels is a hub winding d rum, which, however, must be removed when the vehicle is taken on the highway in the United Kingdom, for a vehicle fitted with it would not conform with existing regulations as to maximum width. This winding drum is bolted to the hub of the wheel and the wheel runs on a floating bush on the hub.
Four arms transmit the drive from the hub to the wheel and, when it is required to use the winding drum, the vehicle being stationary, the pins connecting the driving arms to the wheel are removed, and then all the advantages of transmitting the power from the engine through the gearbox and the differential are obtainable at the winding drum.
Thus, the speed can be varied according to the gear engaged, whilst, if the winding drum on one side only is employed, the speed of operation is doubled by reason of the interposition of the differential gear.
The lowering of the load can be controlled either by the brake or by the reverse gear and, by means of guide pulleys, loading and off-loading in and from any direction are possible. Thus, pipes and timber can be hauled alongside the vehicle and then hoisted on to the platform. The winding drum is also useful for hauling the vehicle out of soft ground. .
The dashboard extends the full width of the vehicle and presents a fiat surface at the rear, whilst towards the front it offers a scuttle tapering towards the radiator. A small instrtiment board carrying the oil gauge and speedotneter, together with the ignition switch, is mounted in front of the driver. Lubrication. of the working parts of the chassis is simplified by the employment of the grease gun throughout.
The frame is of 3/16-in. 'channel-section pressed steel, being 9 ins, deep with flanges 3 ins. wide. It is stiffened by two stamped steel crossmembers, strongly gusseted, and there is a channel cross-member at the front to. carry the forward end of the power unit and a tubular cross-member at the rear, welded to the brackets which carry the rear spring hangers. The petrol tank of 30 gallons capacity is carried at the rear of the frame and a vacuum tank near the engine draws its supply from the main tank.
The front springs are 48 ins, long by 3 ins. wide, the leaves being 7/16th-in. metal. They are secured to the axle by inclined U-bolts, the inclination giving a longer bolt and one less liable to suffer from stretching. The rear springs are 60 ins, long by 4 ins. wide,
• i-in. steel being used in their construction. They are secured to the rear axle casing in •a special forging which had previously been adopted on the Q-type Thornycroft chassis. The housing, or bracket, entirely surrounds the centre of the spring, the top leaf, having four ears which locate the spring lengthwise in the bracket, whilst a strong pin screwed into the upper portion of the bracket bears upon the centre of the spring and secures it in position, a small holding-down plate being interposed between the Spring and the pin. The pin is secured by a locking nut and by a keeper plate which prevents it from loosening. The spring, therefore, has no I5-bolts to stretch and what practically amounts to a pivot point is provided for it. The bracket to which we referral is extended downward to carry the brake cam-actuating shaft, whilst the brake shoe anchorage is also taken on the bracket. This is an expensive form of construction, but is very good, because it eliminates all the possible troubles that are not altogether avoidable when U-bolts are employed.
The wheels are of cast steel and are bolted to cast steel hubs which run on taper roller bearings. They are equipped with 40-in. by 6-in, solid tyres, single on the front axle and twin on the rear. The standard equipment includes a speedometer and mileage recorder and the usual tools and spares. Extra equipment involves extra charge and includes the hub winding-drum, power take-off (which is useful for • operating tipping bodies, driving pumps or any type of tank vehicle, or other special machinery onvehicles used for some specific purposes), driver's cab, front push bar, rear drawbar, trailer brake gear, electric lighting, electric starting, etc. The price of the CC chassis is il,025.
Interesting dimensions beyond those already given are :—Track at front 6 ft. 41 ins., at rear 6 ft. Of in., ground clearance 10 ins., total overall length 23 ft. 2g. ins., width of frame 3 ft. 6 ins., height of frame 3 ft. 1 in., width of cab 6 ft.
6 ins., width over the hubs of the front axle 7 ft. 6 ins. The unladen weight of the front axle is 1 ton 16 cwt. and on ',he rear axle 2 tons