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Dreadnought 1938

Against a background of financial problems and falling UK demand for RSWs, Thornycroft pruned its range of RSWs listed for the British market, then temporarily withdrew them altogether in 1937 and 1938. Exports of such vehicles continued, however. When the firm re-entered the British RSW market in 1939, it did so with a new model called the Dreadnought, reviving a name last used in 1933. Also, by the time the new Dreadnought was available, Thornycroft was back in profit.

This type of Dreadnought was introduced at the Scottish Show in 1938.

Introduced at the Scottish Show in November 1938 for the 1939 model year, the Dreadnought 10 tonner (10,160kg) was a twin steering-axle RSW with forward control. It was powered by a bought-in Gardner 5LW diesel engine, driving through a four-speed gearbox and a two-speed auxiliary gearbox with direct drive and a step-down ratio of 1.5. With two front axles, the modern-looking Dreadnought differed markedly from Thornycroft’s previous RSWs, which had two rear axles. Also, most of Thornycroft’s previous vehicles were powered by engines designed and built by the firm. That a company with Thornycroft’s track record in engine design, development and production should buy in engines for the Dreadnought must have caused comment, not least among the engineers responsible for creating Thornycroft’s engines.

The Dreadnought’s 85bhp Gardner 5LW in-line engine displaced 6,983cc and, unusually, had five cylinders in two separate blocks of two and three, respectively. Thornycroft’s own DC4/1 four-cylinder diesel gave the same power as the Gardner engine, from 25 per cent less swept volume (5,261cc). However, the Gardner’s rotational speed at maximum power would have been around 1,700rpm, notably lower than the Thornycroft’s 2,200rpm, so the Gardner worked less hard. Having decided that 85bhp was the right power for the Dreadnought to give the desired combination of performance and economy, Thornycroft could offer its customers a large, low-revving bought-in engine or its own relatively small, higher revving engine. Thornycroft had to produce what its customers wanted and Gardner, a builder of fine engines, was selected to power the Dreadnought.

The Dreadnought entered production in late 1939, the final one being built in late 1941. A wartime shortage of components limited production to ten vehicles, which, despite the type not being considered successful, found customers who took what was available during the war. The Dreadnought was Thornycroft’s only twin-steer six-wheeler.

 

“Dreadnought” Class 10 ton (10,160kg) chassis, oil-engined type “NF/5LW”

May 1941

Engine

  • Five-cylinder type 5LW watercooled diesel
  • Bore 4¼ins (108mm)
  • Stroke 6ins (152.4mm)
  • Swept volume 6,983cc
  • BHP at 1,000rpm 55
  • Maximum BHP 85

Cylinders
Cast in special iron and in blocks of two and three. A closed chamber is built upon the upper part of the cylinder head in which are housed the overhead valves, valve motion gear, sprayers and patented devices for starting the engine, and for lubrication of the valves. The removal of the cylinder head is a very easy and simple operation because the whole lifts off as one assembly.

Crankshaft
Of nickel alloy steel of 3¼ins (82.6mm) diameter, with six bearings. The journals and crankpins are accurately ground and lapped to fine limits.

Connecting Rods
Of forged alloy steel furnished with a central duct which leads lubricating oil under pressure from the big end to the small end. The big ends are fitted with detachable bearing shells lined with white metal.

Lubrication
Forced feed system from a gear type pump, which delivers oil to the main and connecting rod bearings. In addition the whole of the valve mechanism including the fuel pump cams and rollers are fed with oil under pressure.

Fuel Injection Pumps and Sprayers
The fuel injection pumps are of the well-known Bosch type, one to each cylinder. The pump measures the full charge and forces it through the sprayer into the engine. The fuel sprayers are of Gardner design and manufacture, and require no adjustment.

Cooling
By centrifugal pump.

Transmission

Clutch. Single plate dry type with a particularly smooth action when taking up the drive.

Gearbox
Unit with engine and clutch, and providing four forward speeds and a reverse speed. The gear shafts are carried on ball and roller bearings. The change speed lever is on the driver’s left hand.

Auxiliary Gearbox
Bolted to the rear face of the main gearbox and operated by a separate lever, providing a further reduction of 1.5 which forms an additional range of low gear ratios.

The gear ratios are as follows

 

 

 

Gear

Ratio Main

Ratio Auxiliary

Fourth

Direct

1.5

Third

1.56

2.34

Second

2.75

4.12

First

5.13

7.70

Reverse

7.69

11.53

The overall ratios and approximate speed at engine speed of 1,700rpm are given in mph

 

Speed (mph/kph)

Speed (mph/kph)

Gear

Ratio Main

Ratio Auxiliary

Fourth

30.5/49.1

20.3/32.7

Third

19.5/31.4

13.0/20.9

Second

11.1/17.9

7.4/11.9

First

5.95/9.57

3.96/6.37

Propeller Shaft
Open, tubular type with universal couplings and intermediate bearing.

Axles

Front
Both axle bodies are of special section, forged in one piece. The king pins are supported on taper roller bearings. The track rods are adjustable.

Rear
Of the full floating type with a drop forged casing and overhead worm gear. The worm gear and differential can be withdrawn without removing the road wheels. Both the worm shaft and differential are carried on ball bearings and the road wheels on taper roller bearings.

Springs
Designed to ensure easy riding under varying conditions of load and road surface.

The spring dimensions are

  • Front springs, 3½ins (88.9mm) wide, 3ft 10ins (1.17m) centres.
  • Rear springs, 4ins (101.6mm) wide, 5ft 0ins (1.52m) centres.

Brakes

Foot
Hydraulically operated on all six wheels with vacuum-servo cylinder assistance. One pair of internal expanding shoes operates in each brake drum. Front brake linings are 3ins (76.2cm) wide and rear brake linings 6ins (152.4cm) wide. The diameter of the front and rear brake drums is 17ins (43.2cm).

Hand
Operates on the second steering axle by mechanical linkage without vacuum servo assistance.

Steering

This is of the cam and roller type providing easy control for the driver and operates on the two forward axles by means of interconnected fore-and-aft drag links. The layout gives light and steady steering at all speeds. The turning circle is approximately 78ft (23.8m).

Frame
The frame is of pressed steel with substantial crossmembers giving an extremely rigid construction without employing excessive weight.

Fuel tank
A 30-gallon (136.4 litres) fuel tank is carried on the nearside of the chassis frame. A vacuum tank draws the fuel from the main tank and delivers it by gravity to the injection pump.

Wheels and tyres
The standard equipment is 36ins x 8ins (91.4cm x 20.3cm) tyres, single front, twins rear, fitted to pressed steel disc wheels. All the wheels are interchangeable. The standard position for carrying the spare wheel and tyre is on the nearside of the chassis.

General

Standard body allowance is 1 ton (2,240lbs/1,016kg).

Maximum vehicle running weight with standard equipment, oil, water, and full tank of fuel is 19 tons 9cwt (43,568lbs/19,762kg).

Equipment

A 12 volt, 5 amp electric lighting set combined tail and “stop” light, 105 amp-hour battery, 250 watt dynamo, 12 volt axial starter, electric horn, fuel gauge, spare wheel, tyre and carrier, illuminated instrument panel with speedometer and mileage recorder, oil pressure, brake vacuum and dynamo charge indicators. Radiator blanking-off sheets, mudguards for the first steering axle, kit of tools including jack.

Standard Cab Equipment
Includes sliding windows in doors, safety glass windscreen, electric windscreen wiper, driver’s mirror, licence holder, and front and rear number plates.

Forward Control Cab
A special type of cab has been designed to suit this forward control chassis, and purchasers who desire to make their own arrangements as regards bodywork will find it advantageous to order the Thornycroft cab at the same time as the chassis. However, where the cab is not ordered from us, we wish to make it clear that the chassis is supplied with a front dash, engine bonnet, floor boards for driver’s compartment, mudguards for the first steering axle and combined engine compartment rear panel and cab base. Both the head and side lamps are fixed in position and wired up to the instrument panel.

Information for these pages comes from contemporary Thornycroft technical and other data, as well as contemporary copies of The Commercial Motor.

Download

Dreadnought 1939 outline diagram 14kb pdf