PROGRESS IN THE THORNYCROFT WORKS.
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A New Engine for Heavy Models. Tractor-lorries for 12-ton and 6-ton Loads, and Chassis Modified for London Bus Work.
WE RECENTLY paid a visit to the Basingstoke works of John I. Thornycroft and Co., Ltd., in order to examine the latest types of vehicles which are being built and also to see what progress is being made in the building (If models for the Commercial Motor Show at Olympia.
Perhaps the most interesting of all the new production is the 1.8.4 engine, which is the result of a great amount of experimental work and has been built. following the very successful achievements of an engine of the same type (but smaller power) known as the A.B., and which is now incorporated in the B.T.
type chassis. The new engine is intended for the 6-ton W-type lorry, and for the J-type where particularly heavy work has to be undertaken, as in the case of the new 12-ton tractor-lorry which makes use of a J-type short wheelbase chassis. Many of the ordinary 4tonners are built with the standard type of engine, which has stood up so well
in service that some purchasers do not desire to have the new engine fitted in the machines supplied to repeat orders.
The bore and stroke of the B.B.4 unit are 4/ ins. and 6 'ins. respectively. It has a. remarkable power curve, the b.h.p. being 49 at 1,09.0 r.p.m., 57i at 1,600 r.p.m., and approximately.68 at 2,000 r.p.m. We actually saw the engine under test turning over at considerably above the last-mentioned speed. The consumption of Grade 3 petrol at 1,200 r.p.m. has proved to be
.635 pt. per b.h.p.-hour. The brake thermal efficiency is 22.1 . at 1,030 r.p.m., and the brake m.e.p. 88 at the same speed.
The four cylinders are cast en bloc and mounted on a crankcase of which both halves are cast in aluminium. The detachable heads are cast in pairs, and the valve arrangement resembles that on the B.T. model, the exhaust valves being of the ordinary side-by-side type with tha inlet valves above them and operated by long tappets and rocker arms. The operating gear for the inlet . valves is enclosed by cast aluminium covers with centrally pivoted spring caps to provide access to the rocker lubricators, which are of the wick type, the wick taking the form of threaded copper.
The crankshaft is of the normal type, location being by the .centre bearing The main bearings are of die-cast white metal, the caps being held by bolts which go right through the case and are not liable to pull out, as sometimes happens with stmts.
White-metal-lined gunmetal shells are used for the connecting rods. These have caps held by two bolts, and solid brass adjusting shims are provided. The gudgeon pins, which are hollow, are fixed in the small ends.
The camshaft, with its cams and a spiral gear for driving the oil pump, is cut from a solid bar. The oil pump itself is at the end of a vertical spindle and is drowned with oil. It, is of the gear type, the pinions being_ carried in a white-metal die casting. No governor is fitted, but provision is made for this if it be required.
The pistons, although made of cast iron, are fairly light. They have three very narrow rings at the top, and one wide scraper ring, with a chamfered top edge, at the bottom. This lowest ring skids over the oil film when rising, but scrapes off the oil when descending. The arrangement has been proved to effect a great saving in the consumption of oil and does away with the need for oil baffles.
The timing wheels are of -the single helical type with a tooth width of 1 in. They are held by Woodruff keys and bolted up on the taper.
A novel feature is embodied in the exhaust manifold, in which half the piping is formed by the casting and the other half in the cylinder.
In the case of the short tappets there is one tappet block for each set of four. The tappets themselves have adjustable screw heads and locknnts.
A point of interest in the arrangement of the magneto is that the bracket can be transferred to a second taping on the crankcase, thereby proviVling room for the dynamo bracket if this be required. The magneto is provided with a Simms impulse starter. The circulation of the cooling water is assisted by a pump at the impeller type driven' from the end , of the fan spindle, which itself is provided with a Whittle belt pasking over a pulley at the front of the timing gearcase.
Very great attention has been paid to the question of adequate lubrication. On the inlet side of the oil pump is a long strainer held in position by a spring and so arranged that it can be removed or cleaning through the inspection hole in the crankcase. All oil from the pump is brought to the centre of a muslin bag and Contained in a metal-gauze . case; thence the oil passes through a2large duct in the casting to the main bear: ings. This large filter is situated at the Aide of the inspection cover and is most accessible.
The 12-ton tractor-lorry is a fine example of this type of vehicle. The articulated joint for the. trailer portion consists of a large steel ball in a socket bracket forming a cross-member of. the tractor frame. At one side of this soeket is a square locking bar; one face of which is curved out to allow the bdil to enter or leave the socket. If, however, the locking bar be turned, it effectually retains the ball.
The propeller shaft is provided with extra large 'Hardy joints, their actual diameter now being 11 ins. • Another important feature is the provision of hydraulica...11y operated brakes for the, trailer wheels. These are actuated through the medium of the hand-brake compensating shaft, on which are two levers each connected to a plunger on an oil pump, from which oil is conveyed to poiver cylinders which pull on the trailer brakes. Relative motion between the piping art the tractor ,and trailer is permitted by fleaiblelnetallie tube at the articulating point. In the producticn model taps will be fitted at each end of the flexible portion sa that the trailer may be disconnected without loss of oil.
In *aka to prevent excessive rolling of the body there is a solid rubber cushion at each side of the pivot ball. The trailer frame is dropped at, the centre, and the body has a 16-in. step-up about midway along its floor. The 12-ton tractor lorry, with hydraulically operated brakes is illustrated on page 153. The company are now building a trailer attachment suitable for their RT. chassis, and a drawing of this complete vehicle is reproduced. In the erecting shop we found many J-type chassis, specially built to meet the requirements or Scotland Yard in respect of London buses. .These chassis are of the forward dash type, irs which the driver sits at the side of the engine. The controls are now at the right of
the driver, although they were at,. the left in the first Thornyeroft bus which was put into service. The lock has now been altered to give a turning circle of 56 ft. diameter, whichenables the buses to travel over Richmond Bridge, permission to traverse which is not granted to vehicles with a smaller lock.
The final drive gear eatio has also been altered to 7* to 1, and the new B.B.4 engine is incorporated. There is a standard dynamo driven in line with the magneto, and an additional dynamo is secured to a bracket over the timing case and driven from a V-pulley, which is formed as a one-piece casting with 'a pulley for the fan drive. Starting is facilitated by the fitting of an impulse device to the Simms magneto. We saw over a dozen of these chassis in the shops, and we learnt that one order alone was for 15.
'Elsewhero we noticed a well-con' structed 5.ton trailer for use in conjunction 'with the 6-ton W model. The steering of this was on the Acherman principle, effected by an 'inward extension of the drawbar and connecting links to the stub-axle arms. The brake cable is passed along and through the drawbar and is thus unaffected by it motion. The frame is of rolled-steel channel and the wheels are of the familiar Thornycroft disc construction, internal-expanding brakes being fitted to those at the rear.