Introduced between 1920 and 1922, the Type W lorry was Thornycroft's first post-war lorry, and a contender in the 6 ton (6,096kg) category. Like its J, Q and X stablemates, the W was powered by the well-tried, if old-fashioned 6,256cc T-head 'four' of 40hp, with cylinders cast in pairs. The chassis design followed the usual Thornycroft practice described elsewhere in this website for other Thornycroft lorries, and, like certain other members of the firm's lorry 'family', the W was updated in 1924 with the 6,970cc BB/4 monobloc ioe 'four' giving 58bhp at 1,600rpm.
Forward control 40hp Type W depicted in Thornycroft's 1922 brochure
During a visit to Thornycroft's Basingstoke works in 1923, probably during September, a dynamometer test of the then-new BB/4 was witnessed by staff of The Commercial Motor journal, who commented on its "remarkable power curve" in which the engine gave 49bhp at 1,000 rpm, 58bhp at 1,600rpm and around 68bhp at 2,000rpm. These power-rpm figures show that 1) the power-rpm curve was still rising at 2,000rpm and 2) the curve had not started to flatten off at 2,000rpm, meaning that the engine could have comfortably given more power had it been allowed to run at higher revs. Indeed, The Commercial Motor saw the engine taken to "considerably above 2,000rpm", and it would be interesting to know the corresponding power output. However, in the interests of longevity, Thornycroft fitted a governor its engines, the BB/4 included, to "prevent overspeeding". The governor could be set to suit operating conditions - or removed altogether - a user mod to the Type J during WW1!
The Type W had a relatively short innings because in 1925, the W was discontinued, leaving the Q lwb as Thornycroft's 6 ton (6,096kg) contender, also powered by the BB/4 engine.
Specification of Thornycroft 5½/6ton Chassis, Type "W" March 1924
For a nett load of 120cwt (6,096kg) in an open lorry body, or 110cwt (5,588kg) in a van body.
Chassis Weight, in running order, 78cwt (3,962kg).
Gross Load, including cab and body, 140cwt (7,112kg).
Total Laden Weight 216cwt (10,973kg).
Front, 69 cwt (3,505kg).
Rear, 149cwt (7,569kg).
50hp (type BB/4). Four-cylinder, monobloc with detachable top. Inlet valves over the exhausts. Bore 4¾ins (121mm) x Stroke 6ins (152mm).
Damp-proof high-tension magneto.
Of improved float feed type. A pilot jet is fitted for starting and slow running.
The carburettor throttle is controlled by a screw for setting the slow-running lever on the steering column and also by a foot accelerator pedal.
The capacity is 20 gallons (91 litres), and a very large filler is fitted which does away with the need for a funnel.
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.
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, 1.8mph (2.9kph); first 2.2mph (3.5kph); second 4mph (6.4kph); third, 6.8mph (10.9kph); fourth, 11.6mph (18.6kph).
Operated through a gate type quadrant.
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 10.66 to 1.
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.
A sheet metal mud-shield under the fore part of the chassis protects the mechanism from dust and mud.
The axle body is of H-section steel, drop forged in one piece. The swivel arms are of the central pivot type which render steering very easy in spite of the weight of the vehicle.
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.
This is fitted with ball bearings and ball thrusts, which help to render the steering very easy.
The minimum width of road for reversing direction without using reverse gear 57ft (17.4m).
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.
Solid rubber singles on front wheels, 140 x 720mm; twins on back wheels, 160 x 850mm fitting sizes.
Minimum clearance underneath chassis, fully laden, about 10ins (254mm).
14ft 6ins (4.42m).
Front wheels 5ft 11½ins (l.82m.). Centre-to-centre of twin tyres on back wheels 5ft 10ins (1.78m).
Chassis diagram 104kb pdf
Dimensions information 98kb pdf