ACCESSIBILITY OF THE LIGHT VAN CHASSIS.
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The Importance of Arranging the Components so as to Facilitate Adjustments, Replacements and Repair Work.
THE present design of the engine and chassis of the 'light delivery van, suitable for carrying loads of 10 cwt. to 20 cwt. at high Speeds, has undoubtedly owed a great deal to the experience gained by manufacturers of pleasure cars. Unfortunately, in addition to inheriting a number of good features, the light van includes several bad points which have likewise been passed on, and, perhaps, the worst of these is lack of accessibility. This is a matter of • considerable importance, because the idyllic state of-affairs in which the chassis would require no attention until worn out has not yet come to pass, by any means. Consequently, the design should be arranged so as to. facilitate the adjustment or replacement of any one of the working parts with the minimum of. trouble. Otherwise, adefective vehicle may be .laid,up far a considerable period and the delivery of goods dela:yed thereby.
In considering this question, it is important to ,remember that, . in addition to the fleets which' are employed by big stores, there is a large number of small firms who employ . three or four vehicles. To these people it iss absolutely essential that a vehicle should not be laid up for any considerable time, because the loss of one van to a firm which employs, say, four vehicles means a reduction in delivery capacity of 25 per cent.
The mo§t important point to consider in the general chassis lay-out is probably the question of whether the gearbox should he a separate unit, situated near to the centre of the frame, or whether it should be built on to the engine crankcase. The latter method is deservedly popular with manufacturers, because it simplifies and cheapens the construction and reduces
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the number of shafts and joints required in the transmission. However, it must be admitted that unit construction usually leads to a very inaccessible clutch, and in many cases, the position of the gearbox is such that adjustments are not very easy to carry out. These troubles can be reduced by securing the gearbox to the crankcase through the medium of two large webs, leaving an open clutch pit, instead of completely enclosing the flywheel.
Another important point in this connection is the desirability of making it possible to lift out the complete engine and gearbox unit without undue trouble. This job should not require more than 30 minutes' time all told, but there are, unfortunately, a number of chassis on the market in which the operation would occupy a very long period, owing to t h e necessity for dismantling the radiator and removing the dash with all its connections. The writer even knows of a case in which the design of the propeller shaft and universals is such that it is actually necessary partially to dismantle the back axle before t h e gearbox can be lifted out.
• The removal of the radiator seems inevitable before the engine unit can be taken out, but every care should be taken to simplify this operation by the provision of sensible pipe joints and a suitable design of radiator fixing. It should certainly not be necessary to disturb the dash in any way. In the case of a large fleet it will be well worth while to keep a spare engine and gearbox unit in stock, so that, if the design has been 'properly thought out, the defective unit can readily be removed and replaced in a matter of a couple of hours.
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ed spcce cannot readily be re often difficult to reach.
Of course, there are several minor defects in the engine which do not necessitate its complete removal, and their rectification can be greatly simplified by careful design. For example, sine frequently sees the detachable head encumbered by innumerable fittings, which could very ,well be placed elsewhere and which greatly increase the labour involved in removing the bead. It is suggested that it might be worth while to incorporate valve caps in the head, so that the presence of one defective valve would not necessitate the breaking of an important joint and the removal of anything from 16 to 20 nuts.
Tappet adjustment is called for at frequent intervals, a fact which seems to have escaped the attention of many. designers. The space available is often so limited that it is almost impossible to use ordinary spanners to adjust the tappets. Special spanners may be supplied for this purpose, but are always a bugbear because they are never to be found when urgently wanted.
Much could also be said with regard to fuel and ignition systems. Carburetter jets are often very badly placed, insufficient space being left below the carburetter. Filters are often hidden away so that the removal of the gauze becomes a very difficult matter. The magneto should be placed with the contact-breaker cover facing outwards so that the points can readily be seen and adjusted. As regards the water-circulation system, pumps i have proved such an unmitigated nuisance n many instances that it would undoubtedly be desirable to do without these auxiliaries altogether. If a pump is considered necessary, it should be so placed that the glands can be easily adjusted or repacked. With regard to the clutch, it should be a comparatively simple matter to provide an easy means for adjusting the withdrawal gear, to compensate for the
wear which takes place in the lining. When this wear becomes considerable, it will, of course, be necessary to re-line the clutch, and here the separate gearbox or open clutch pit proves a great advantage.
As regards the gearbox, selector gears require attention, and a large cover plate should be provided, through which the mechanism can be set to secure correct meshing of the gears. Very frequently, the box is so arranged that -it is almost impossible to tell whether the gears are meshing correctly or not. Universal joints present a number of problems. With the Hotchkiss type of drive usually employed, it should be possible to arrange these joints so tliat, by slacking back a few nuts, the propeller shaft can be removed complete. Unfortunately, the design of many mechanical joints is such that either the gearbox has to be moved forward or the back axle moved backward before the shaft can be got out. In this and other respects, the fabric joint presents many advantages, and it is certainly quite capable of doing the work in a light-van chassis. The majority of light vans run on pneumatic tyres, and the possibility of punctures must not be neglected. In this respect, there does not seem very much to choose between the demountable rim and the detachable wheel. Brakes are also very important, and it is essential that conveniently placed hand-adjusting nuts should be provided. In addition, it is as well to provide means whereby the levers on the cam spindles can be altered in their positions relative to the cams, so that the full thickness of the brake lining can be utilized before it is replaced. Ease of replacement should also be considered, and in this respect the type of lining which is secured at the ends by means of studs possesses considerable advantages compared with the riveted variety.