The forward control Type CC was introduced in 1927 as the 7 ton (7,112kg) lorry in Thornycroft’s model range, inaugurating a new load capacity in response to market demand. The vehicle was designed to give the fullest possible loading capacity, whilst conforming with the maximum legal load limits then in force in the UK, which were 12 tons (12,192kg) for the total axle weight with a maximum of 8 tons (8,128kg) for any one axle. The weight of the CC chassis was 4 tons 4cwt (4,267kg), and, allowing for a body weight of 20/21cwt (1,016/1,067kg), a margin of 6.75 tons (6,858kg) was left for useful load. Where the total load limit was more than 12 tons (12,192kg), the vehicle was capable of carrying 7 tons (7,112kg).
The CC was a larger brother of the JJ, and like the lower rated JJ, the CC was powered by the new 6,972cc MB/4 four-cylinder in-unit engine which was introduced in 1927; this was the largest of three four-cylinder in-unit petrol engines covering the needs of Thornycroft’s model range. The MB4 gave 50bhp at 1,000rpm, rising to 60bhp at 1,800rpm.
While the JJ was designed for use with solid or pneumatic tyres, the CC was expressly designed for solid tyres, mainly because of the greater overall vehicle width that pneumatics would have imposed. The vehicle was geared to reach a modest 16.75mph (27kph) in top gear at an engine speed of 1,500rpm, however one could hardly expect high performance from a mere 60bhp shifting no less than 12 tons (12,192kg). Power was transmitted from the gearbox to the back axle via a two piece propeller shaft, the rear end of the front shaft was supported by an intermediate ball bearing and each shaft portion was supported by universal joints. In those days, crude canvas u/js were not uncommon, but they were not used on the CC and metal ones were used to give the required strength.
The CC was fitted with a hub winding drum attachment for the rear wheels. This device had to be removed when the vehicle was taken on public roads in the UK as it pushed the CC’s maximum width to beyond the legal limit. The winding drum was bolted to the wheel hub and a simple arrangement was made whereby the shaft drive could be quickly disengaged from the wheel and directed entirely to the hub for driving the winding drum. A drum on either side could be used, and on both sides at once. If only used on one side, then the speed of the drum was doubled compared to use on both sides by the interposition of the differential. By means of guide pulleys, loading and off-loading was possible from any direction. Thus pipes and timber could be hauled alongside the vehicle and then hoisted up on to the platform, making the vehicle was self-loading. The winding drum was also useful as a winch for hauling the vehicle out of soft ground.
In keeping with its time, dashboard instrumentation was very simple, and comprised a speedometer/mileometer and an oil pressure gauge. Even in 1927, electric lighting and starting were optional extras, which means that some drivers had to start nearly 7 litres of engine by hand swinging the starting handle!
A power take off could be had at extra charge which was useful for operating tipping bodies, driving pumps for tanker vehicles, or other specialist machinery. Also, as an extra, a trailer rear drawbar was available as well as a trailer brake attachment. The CC had the highest rated load of any MB/4-powered vehicle, and with the added burden of a trailer the whole outfit must have seemed woefully underpowered even by the modest standards of lorries in 1927, and frustrating for drivers of the faster cars then on offer.
The CC had a short production life and was withdrawn in 1928, the year after its introduction. This left a gap in the four-wheel category of 7 tons (7,112kg) or thereabouts, until the introduction of the 6.75 ton (6,858kg) Taurus JD in 1932.
Specification of Thornycroft Type “CC” Forward Control Chassis (Petrol) September 1928
To carry a net load of 7 tons (7,112kg), with a body allowance of 20 to 21cwt (1,016 to 1,067kg).
36.2hp (RAC) type "MB4", watercooled four-cylinder petrol engine, bore 4.75ins (120.7mm) x stroke 6ins (152.4mm), developing 60bhp at 1,800rpm. Compression ratio is 4.4 to 1. The four cylinders are of the monobloc type with two detachable heads. The valves have double springs, and the Thornycroft standard roller tappets, with accessible adjusting nuts, are employed. The pistons are of cast iron with three piston rings, but, if desired by the purchaser, aluminium pistons can be supplied. The connecting rods are of duralumin, the caps being fastened by two bolts. Big end bearings are gunmetal shells with white metal linings. The crankshaft is carried in three main bearings.
Lubrication of engine
Four gallons (18.2 litres) of oil are carried in the sump for lubrication and the oil pump is submerged in the oil. It supplies the oil to a channel which runs end to end of the engine at a pressure of 15lb/in2 (1.034 bar). From this oil channel the lubricant passes to the main bearings and through a drilled crankshaft to the big-ends, the cylinder walls and small-end bushes being lubricated by splash. The camshaft bearings are pressure-fed and the surplus oil passes to the timing gear. No copper pipes are incorporated in the lubrication system, except the external pipe to the pressure gauge on the dashboard. A dipstick is fitted with maximum and minimum marks and a test cock is fitted in the crankcase to indicate the high level point of oil. An oil filter is fitted.
Lubrication of chassis Grease-gun system throughout.
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 dynamo between the driving gear and the magneto when an electric lighting system and engine starter are fitted. Advancing and retardation of the ignition are effected automatically.
A Zenith carburetor with a hot-spot induction manifold ensuring complete vaporization. The throttle is controlled by an accelerator pedal, a setting for slow running being obtainable through a lever on the steering column.
A propellor type pump is run in tandem with the cooling fan. Tension of the fan belt is regulated by means of an adjustable flange on the driving pulley.
This is of the vertical gilled tube type. The radiator has removable top and bottom vessels, enabling new tubes to be easily fitted.
30 gallon (135.8 litre) tank mounted at the rear of the frame, and a vacuum tank near the engine draws its supply from the main tank.
A dry, single plate clutch faced with asbestos fabric. The driven member is light and the clutch stop being efficient, changing of gears is simple and speedy.
Mounted on the rear end of the engine crankcase ensuring alignment. Has four forward speeds and a reverse, the top gear being direct drive.
The gear ratios are:
At 1,500rpm of the engine, with 40ins x 6ins (101.6cm x 15.2cm) solid tyres solid tyres, the vehicle speeds are:
The drive is taken through an intermediate propeller shaft connected to the gearbox by a Spicer metal 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 attached to the frame, this now being the general practice on Thornycroft vehicles that have an intermediate shaft. The propeller shaft is tubular and has two enclosed, metallic universal couplings, one of them being telescopic
Power from the propeller shaft passes to an overhead worm gear in the differential and then to floating drive shafts. The final drive to the rear wheels is though external dogs, the drive shafts being capable of removal without taking off the axle. The differential reduction is 10.66 to 1.
In addition to the normal wheel brakes, a transmission brake is fitted. The transmission brake acts upon the intermediate propeller shaft and is a Thornycroft speciality, which consists of a single ring of steel 7ins (17.8cm) wide and 0.375ins (9.53mm) thick, lined with asbestos fabric, held at its central point (with means for adjusting it concentrically with the brake drum) and pinched together by moving fingers operated through rods from the brake lever.
Fitted outside of the frame, just forward of the radiator and embraces a worm and complete wheel. This vehicle has a turning circle of 60ft (18.3m).
Channel-section pressed steel 0.1875ins (4.76mm) thick, 9ins (22.9cm) deep, with flanges 3ins (10.6cm) wide. It is stiffened by two stamped steel cross-members, 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 power unit is suspended on three points with rubber buffers interposed between engine arms and the brackets on the frame. The rubber pads between the frame brackets and the engine bearers are 1in (2.54cm) thick and are carried in two dished plates, whilst a rubber washer between two dished plates is interposed between the securing plates and engine bearer. The power unit is readily removable from the chassis.
Spring dimensions are as follows
Front 48ins x 3ins (121.9cm x 7.62cm). Leaves are 0.4375ins (1.11cm) thick
Rear 60ins x 4ins (152.4cm x 10.16cm). Leaves are 0.5ins (1.27cm) thick.
Wheels and tyres
Cast steel wheels with solid rubber tyres, 40ins x 6ins (1,016mm x 152.4mm) singles front, 34ins x 5ins (863.6mm x 127mm) twins rear. All wheels are bolted to cast steel hubs which run on taper roller bearings.
A useful attachment for the rear wheels is a hub winding drum 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 to existing regulations as to maximum width. The winding drum is bolted to the hub of the wheel and the wheel runs on a special 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 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 the 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.
Wheelbase 16ft (4.88m).
Front wheels, 6ft 4.75ins (1.95m)
Rear wheels 6ft 0.25ins (1.84cm).
Ground clearance 10ins (24.4cm).
General measurements and weights:
Standard equipment includes a speedometer, mileage recorder as well as a set of tools and consumable type spares. Additional equipment available at extra charge includes hub-winding drum, power take-off, driver’s cab, front push bar, rear drawbar, trailer brake gear, electric lighting, electric starting, etc.
Electric lighting and starting
Provision is made to supply at an extra charge either a lighting and starting set or a lighting set only, the dynamo being mounted in tandem with the magneto and the starter bolted direct to the engine casing.