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Type J

By 1912, Thornycroft was well-established as a successful manufacturer of heavy vehicles. Also, the firm had strengthened its reputation by winning a number of awards for the performance of its vehicles in various trials, and Thornycroft's activities had attracted the attention of the War Office.

Type J high-sided lorry from Thornycroft's 1924 brochure

Thornycroft built on its success when it introduced the famous Type J lorry in 1913. The J appeared before the widespread use of diesel engines for road use, and so, like other lorries of its day, it was petrol driven. Although the J was originally built for a load capacity of 3.4 tons (3,454kg) and powered by a 30bhp engine, by 1919 capacity had risen to 4 tons (4,064kg) and power came from the massive 40hp T-head M/4 engine of 6,256cc whose four in-line cylinders were cast in two separate blocks. Power from the fore-and-aft facing engine was transmitted to a worm-driven live back axle via a four-speed gearbox and propeller shaft. The J's specification included solid rubber tyres, with twins on the back wheels and, according to data published in 1915, the J could be adapted to run on kerosene (i.e. paraffin) if required. A hand throttle was provided, in addition to the normal pedal accelerator, and the ignition timing was controlled by a lever mounted on the steering wheel hub. Eventually, Thornycroft fitted its vehicles with automatic ignition timing, although the J retained manual timing over its production life. The J's HT magneto ignition, rear-wheel only brakes, solid tyres and other features were typical for their time, and were retained until 1926 when the J went out of production. Drum brakes only on the back wheels seem woefully inadequate by today's standards, but it should be remembered that the J travelled very sedately and traffic densities were much lower when the J was introduced. The Type J chassis was used for buses as well as lorries.

When WW1 broke out in August 1918, the War Office was seriously short of subsidy vehicles which it could call up for service, as the subsidy scheme had been a failure. The War Office therefore resorted to impressing a large number of lorries and it instructed Thornycroft to supply its entire Type J output for military use, the first batch being delivered on 8 September. Later on in the war, Thornycroft was allowed to supply small numbers of the Type J to private operators, subject to War Office approval.

By September 1915, Thornycroft was delivering around 28 Type J lorries a week to the War Office and, during WW1, the type served in France and elsewhere. Thornycroft produced about 5,000 Type J lorries during the war, and the firm's wartime output of Js makes an interesting comparison with the production of other British manufacturers. For instance Commer (a contraction of Commercial Cars) produced over 3,000 4-tonners (4,064kg), Dennis produced around 7,000 3½ ton (3,556kg) subsidy lorries and Leyland built nearly 6,000 3 ton (3,048kg) subsidy lorries. Other manufacturers, also, produced lorries for the War Office during WW1. In common with other firms, Thornycroft faced difficulties during the conflict due to shortages of labour and materials. Despite problems, however, the firm was able to extend its Basingstoke factory to meet wartime demand for its output which, as well as lorries, included munitions and other products. By 1919 the works occupied some 12 acres (4.86 hectares).

After WW1, large numbers of ex-WD vehicles became available to civilian operators at good prices. There was, nevertheless, a market for new vehicles, and Thornycroft manufactured a range of lorries which included the well-tried 40hp Type J. The standard wheelbase of the J's chassis was 13ft 7.5ins (4.15m), but, by 1919, a 14ft 4.5ins (4.38m) lwb option was added for buses & charabancs (an early form of motor coach, from 'char-à-bancs', French for 'carriage with benches'). Chassis used as charabancs had bodywork for up to 30 passengers, while the Type J chassis could also carry a double-deck body for 16 passengers in the lower deck and 18 on the upper deck.

There was interest in the UK and France in the use of producer gas as a fuel for road vehicles, generated on the move by on-board gas-production plant. This method of fuelling was thought to have potential in countries where other fuels (e.g. petrol) were difficult to obtain. Equipment for the production of producer gas was built and fitted to a 40hp Type J lorry in 1921/22, and the vehicle was sent to France for trials. Thornycroft did not pursue the idea and continued producing petrol-driven lorries; however the use of vehicles converted to run on gas re-surfaced during WW2, when petrol was in short supply.

Thornycroft's Type J 4 tonner (4,064kg) faced competition from several British firms. Numerous vehicles were exhibited at the Commercial Motor Vehicle Show at Olympia in 1923, and other British 4 ton (4,064kg) lorries at the Show comprised ten petrol-driven vehicles (Albion, Bristol, Commer, Hallford, Karrier, Lacre, Leyland, Maudslay, Pagefield and Tilling-Stevens) and five steam vehicles (Allchin, Atkinson, Clarkson, Clayton and Mann). However, of the foreign vehicles exhibited, only Pierce-Arrow from the USA offered a 4 tonner (4,064kg). Most of the vehicles mentioned had platform lengths of around 13ft (3.96m). There were no diesel vehicles.

In 1924 the J was updated with the more powerful, newly introduced, 50hp BB/4 engine; the J's load capacity was unchanged at 4 tons (4,064kg). The four-cylinder BB/4 was radically different to the 40hp M/4 engine that it replaced, with monobloc cylinders and ioe valves - the latter feature, incidentally, was used on Rolls-Royce and Bentley cars during the 'forties and 'fifties. Despite its 50hp designation, the BB4 gave 58bhp if pushed to 1,600rpm. With its impressive 6,970cc, it was 11 per cent bigger than its 40hp predecessor, yet, by today's standards its power output would only do justice to a small car! At a rather quick 1,600rpm, the 1926 Type J could manage a stately 23mph (38kph) shod with 40ins (1,016mm) tyres. Thornycroft's 1926 brochure quotes speeds at 1,200rpm! Even as late as 1926, electric lighting was an optional extra, as was a speedometer or mileometer.

A plain lorry platform bodied 40hp Type J in the livery of Armitage & Rigby, Warrington. HMAS

The J's 4 ton (4,064kg) capacity was more than doubled by a six-wheeled articulated version of the J, to 8.5 tons (8,636kg), and the J was offered in this form in 1924, with solid tyres and the 50hp BB/4 engine. The tractor's wheelbase was reduced to 12ft (3.66m) from the four-wheel lorry's 13ft 7.5ins (4.15m).

The 14ft 4.5ins (4.38m) lwb, previously a chassis option, became the standard lorry wheelbase in 1926, the year in which Type J production ended. The vehicle was available with solid tyres, but by that time buyers could opt for Dunlop pneumatic tyres for an extra £94. As freight and municipal vehicles, Thornycroft offered no less than 12 alternative bodies - ie. three van body options, three tip wagon options, a watering wagon, and five types of lorry (plain lorry platform, brewer's lorry, open-sided lorry, hinged-sided lorry and standard War Department body).

 

Specification of Thornycroft 3½/4ton (3,556/4,064kg) Chassis (March 1924)

Type "J" War Department Model

For a nett load of 80cwt (4,064kg) in an open lorry body, or 70cwt (3,556kg) in a van body.

Chassis Weight, in running order, 65cwt (3,302kg).

Gross Load, including cab and body, 95cwt (4,826kg).

Total Laden Weight 160cwt (8,128kg).

Axle Weights (Laden)

Front,44cwt (2,235kg). 

Rear, 116cwt (5,893kg).

Engine

50hp (type BB/4). Four-cylinder, monobloc with detachable top. Inlet valves over the exhausts. Bore 4¾ins (121mm) x Stroke 6ins (152mm). If preferred and specified when ordering, we can supply our well-known 40hp (type M/4) engine, as previously fitted into this chassis.

Ignition

Damp-proof high-tension magneto.

Carburettor

Of improved float feed type. A pilot jet is fitted for starting and slow running.

Control

The carburettor throttle is controlled by a lever on the steering column and also by a foot accelerator. The magneto is controlled by a second lever on the steering column.

Petrol Tank

Placed on the dashboard where it is accessible for easy filling, and allows of a constant gravity feed to the carburettor under all conditions. The capacity is 20 gallons (91 litres), and a very large filler is fitted which does away with the need for a funnel.

Clutch

Of the cone type. A pressed steel cone lined with ferodo engages the cast-iron flywheel. This is of large diameter, ensuring smooth running, absence of slip, and maximum life of clutch lining. The clutch springs are easily accessible for adjustment. A large and efficient clutch stop is fitted to facilitate gear changes. Between the clutch and the gearbox, a leather disc-type universal coupling is fitted.

Gearbox

A one-piece casting with large inspection cover. Ball bearings on primary and secondary shafts with ball thrust behind brake drum. The drive on top is direct with three indirect gears and a reverse. At 1,000rpm of engine the road speeds are as follows: Reverse, 2¼mph (3.6kph); first 2¾mph (4.4kph); second 5mph (8kph); third, 8½mph (13.7kph); fourth, 14½mph (23.3kph).

Change Speed

Operated through a gate type quadrant.

Final Transmission

Live axle fitted with overhead type worm gear. The central portion of the axle is composed of a cast-steel casing of ample strength into which is fitted the differential worm gear, carried in a self-contained housing which, without taking the load off the road wheels, can be removed bodily at any time. Standard ratio 8.25 to 1.

Brakes

Two brakes are fitted: a foot brake, of the contracting type, operating on a drum at the rear end of the gearbox; and a hand brake of the expanding type, which is applied on the rear wheels direct. The drums are of very large diameter. Both brakes can be adjusted for wear by hand without the use of tools.

Mud-Shield

A sheet metal mud-shield under the fore part of the chassis protects the mechanism from dust and mud.

Front Axle

The axle body is of H-section steel, drop forged in one piece. The swivel arms are of nickel steel, with ball thrusts on the pivot pins taking the weight, giving easy steering.

Frame

Channel section pressed steel. Strong, but light. The engine and gearbox under-frame is suspended on the three-point system, so that twisting of the frame members due to uneven road surfaces has no harmful effect whatever.

Steering Gear

This is fitted with ball bearings and ball thrusts, which help to render the steering very easy.

Steering Lock

The minimum width of road for reversing direction without using reverse gear: Standard chassis 50ft (15.2m); 14ft 4¼ins (4.38m) wheelbase chassis 52ft (15.8m); 15ft 6ins (4.7m) wheelbase chassis 56ft (17.1m).

Wheels

Nominally 34½ins (876mm) diameter over tyres on front, 41½ins (1,054mm) over tyres on back. Of cast steel with solid rubber tyres. The wheels are carried on phosphor-bronze floating bushes of large size.

Tyres

Solid rubber singles on front wheels, 120 x 720mm; twins on back wheels, 140 x 881mm fitting sizes.

Clearance

Minimum clearance underneath chassis, fully laden, about 12ins (305mm).

Wheel Base

Standard chassis, 13ft 7½ins (4.15m). Extended wheelbase chassis for coaches or omnibuses, 14ft 4½ins (4.38m), or 15ft 6ins (4.72m).

Track

Front wheels 5ft 7¼ins (l.71m.). Centre-to-centre of twin tyres on back wheels 5ft 6ins (1.68m).

 

Downloads

Chassis diagram 115kb pdf

Dimensions information 124kb pdf