AN UNUSUAL SIZE OF PETROL CHASSIS.
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A Well-designed Chassis Built to Carry 51-61-ton Loads, the Watson Possesses a Notable Rear Transmission Unit.
ONE USUALLY considers that the useful sphere of employment of the petrol velikle extends from the chassis which is capable of carrying a mere few hundredweights up to that which can accommodate a gross load of 5 tons. As a matter of strict fact, there are very few petrol vehicles which are designed to
carry loads beyond 4 tons, the steam wagon generally being considered to be the type of vehicle which can best handle
loads above that weight. The petrol vehicle and the steam wagon each possesses characteristics which render it heat suited to distinct fields of utility, although it would perhaps be difficult to fix a. definite line of demarcation between the types. It may, or may not, be an unwritten law that one type is capable of fulfilling certain requirements better than the other, although instances will assuredly crop up to disprove the generally accepted theory.
There is no reason, to the best of our knowledge, why the petrol vehicle of a greater carrying ,capacity than those types which are in general employment should not prove efficient and economical for certain classes of work where heavy loads have to be regularly carried. It is for this reason, we feel sure, that the Watson commercial vehicle, which has been introduced by Henry Watson and Sons, Ltd., High Bridge Works, Newcastle-on-Tyne, will meet with approval at the hands of users who have to transport heavy loads over fairly long distances.
It was in January, 1920, that the company introduced their 3i-40on chassis, and the larger brother of this vehicle was placed on the market two years later. The two models possess a striking resemblance to one another ; in fact, most of the features embodied in the one type are to be foundin the other, the chief diffrrences being brought about by the
added load whichthe 'larger model is built to carry.
The engine is g four-eylinder unit, with the cylinders cast in pairs, the bore being 120 ram. and the stroke •140 mm. The cylinders are of the L-fieaded type, and the unit develops 47.5 h.p. at 1,000
r.p.m. The crank chamber is 9f cast steel, aluminium being only used for doors and covers throughout the chassis. This chamber is provided with two large inspection doors which enable the bigend bearings to be readily examined. The crankshaft is supported from the upper half of the crank chamber by five bearings of ample dimensions. A large diameter ball thrust race is provided at the flywheel end to take •up all end thrust. The valves, which are of the tulip pattern, are protected by east aluminium covers. The camshaft is carried in three phosphor-bronze bearings, and lubricant is carried along special grooves. •
The -water-cooling pump is of the centrifugal type, the impeller being of gunmetal and running in a east-iron easing. Engine lubrication is effected by a geared pump driven by a vertical shaft off the camshaft by skew gearing. The pump draws its oil supply fromthe engine .sump and thence forces it through a copper tube to a large disc oil filter on the right-hand side. of the engine. From the filter the oil is forced through external copper piping . to a return head, and thence to the main oil pipe running alongside the crank chamber. It is then forced through the drilled crank chamber to the main bearings, thence through the drilled crankshaft to the big-end bearings, being thrown on to the cylinder walls and to the gudgeon, pin bearings. Splash deflectors are fitted on the base of the cylinders, and, a pressure tell-tale gives the driver an indication that the system is working satisfactorily-.
The carburetter is a Clam:kJ-Hobson, and a governor of the. Harenell type can be fitted if required. The induction piping is connected to the inlet manifold, which is an integral part of the exhaust manifold. In this way the incoming charge is heated at the neck of the pipe
before it enters the cylinders, wet mixture, with consequent excessive sooting of the piston heads and pitting of the valves, being thus avoided. The engine and gearbox are ,carried on a long sub-frame which is supported on heavy angle brackets suspended from
the chassis cross-menibers. The frame -and cross-members are of rolled steel channel, the dumb-irons being of cast. steel, From the engine the drive is taken by -a large diameter clutch of the cone type to a four-speed-and-reverse gearbox which gives a direct: drive on top gear. The gear reductions from engine to road wheels, and the corresponding vehicle
• speeds in m.p.h. at an engine speed of • 1,000 r.p.m. are as follow :— Gear Vehicle Reductions. Speed.
1st speed ... 36.6 to I. 3.25 2nd „ ... 22.2 to 1 ... 5.35 3rd „ 13,9 to 1 8.55 4th „ 8.48 to 1 ... 14 Reverse ... 29 to 1 ... 4.1
The universal joints fitted to both ends of the cardan shaft are of -the De Dion jaw type, with case-hardened steel crosshead pins. The driving dies are of . phosphor-bronze and slide in casehardened Ubas steel jaws. The dies have spiral grooves •scored internally, and cross-cuts externally, for the purposes of lubrication.
Two heavy radius rods are hinged to the chassis frame members from ballsocketed heavy-anchor brackets, which are situated on the centre, line of the for-ward universal joint. The radius rods • are checked into the rear dead axle and each is secured by a large centre bolt, and by the four bolts through check plates, which also apt as the rear spring ietaining bolts, The radius rods take all torque, driving and braking stresses and 5-elieve the springs from all but loadarrying stress. The radius rode carry the live aide casing and also the brackets or the hinge pins of the side 'brake shoes.
The live axle and differential easing are supported by the radius rods, to which they are bolted at each end throughheavy feet, and stayed at the eentre by the perch bar.
The power is transmitted front the cardan shaft to the bevel pillion shaft, to which the bevel pillion itself is secured by pinned lock-nuts. The bevel pinion drives on to the crown wheel, the gear reduction between them, which is small, permitting of a special tooth pitch, which enables two teeth to be constantly in . mesh between the iiinion. and crown wheel.
The differential is of the sun and planet type and has four star pinions. Tapered floating shafts are secured to the spur pinions, and drive on to internally cut gear rings, which arc totally enclosed in steel grease-retaining covers.
The subject of braking has received special attention. The foot brake is of the metal-to-metal, external-contracting type. It is fitted immediately behind the rear univers.al, and its operation, therefore, is independent of failure of the eardan shaft. The hand brake is of the internal-expanding type.
The steering is of the irreversible worm and segment type. An exceptionally largo lock is provided, the turning circle of a etanclard chassis being 53 ft.
The springs are of ample dimensions, those at the rear being slung from shackles at both ends, and thus subject to loading stress only.
The road wheels are of eastesteek.thoso at the front having Y-shaped spokes, whilst the rear wheels are of the solid disc type, with. radial stiffening webs. The tyres with which they are fitted are 934 mm. by 140 mm. at the front and 1,013 min. by 140 mm. twin at the rear.
There is one modification which the plan view on the previous page does not depict, and that is that the front axle has been set back 1 ft. 6 ins, in order to secure better distribution of the load. The wheelbaseof the &cassis is 15 ft. and its track 5 ft. 1* ins.
The general design and constniction of the 51-644on -Watson chassis are in strict accordance with the best traditions of
British engineering practice. It is of robust and workmanlike build throughout and incorporates distinctive fe'aiures which have proved their worth under actual service conditions..