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By A. A. TOWNSIN, A.M.I.Mech.E.
A. LTHOUGH the 25-seater coach on Thames Trader 3-ton, 138-inwheelbase chassiS announced in our issue of May 11 'Marks the return of its makers, Kenex Coachwork, Ltd., to the manufacture of a size of. vehicle with which they were associated in the early post-war period, it is entirely new in conception as well as design.
The present-day Kenex factory at Dover is largely geared to the conversion of light vans to buses in the 12-seater class, motorized caravans and so on. This is done on quite a large scale, using something approaching mass-production methods, although the variety of models for conversion and the diversity of finished products precludes the use of anything like a rigid production line system.
A good deal of thought has been given to modern production methods and this outlook is reflected in the character of the 25-seater. For example, the traditional type of coachbuilding using wooden framework plays no part in its construction. The concern has used glassfibre mouldings for such items as the roof panels on caravan conversions for some time, and it was a natural move to extend this to the manufacture of the frontand rear-end assemblies, among other parts, of the new model. The manufacture of body framing is an activity which is not required to any large extent for the concern's other products because of the general use of their structure as delivered from the vehicle, manufacturers. It was accordingly decided to purchase complete sets of cold-drawn steel framework from Metal Sections, Ltd. Assembly is carried out at Dover, using bolts and self-locking nuts.
Framing largely composed of straight sections was deliberately chosen for ease of manufacture and to enable standardized window outlines to be used. This has resulted in the side view of the
vehicle being largely .dominated by horizontal and vertical lines, whereas the front-end styling is almost entirely coinposed of curves. The contrast is made more obvious by the use of small side windows in conjunction with a large three-piece curved glass windscreen. Cantrail windows are provided and give a light and airy interior, but both appearance and sideways vision from the passenger seats would be improved by the use of fewer, larger side windows.
The general appearance is, however, quite pleasing. Particularly effective is the Way in which the windscreen assembly, although a production item designed for a larger coach of another make, has been made the basis of an attractive front-end design. Its height gives exceptional forward visibility for the passengers and the effect of a relatively shallow roof panel gives an up-to-date frontal appearance.
Access to the interior is easier than on many larger coaches. The use of the low-frame version of the chassis enables the doorway to have two steps of reasonable depth. It does, however, require comparatively large wheel-arches protruding into the interior. On the prototype vehicle the seats immediately behind the rear wheels have, as a result, rather limited leg room. It is proposed to 7engthen subsequent bodies by some S in. so that it should be possible largely to overcome this problem as well as increasing the size of the luggage boot.
This modification will also, no doubt, enable the general spacing of the seats, which is already adequate, to ?.,e improved. The seats themselves are comfort able and well-shaped. The interior trim is neatly carried out with PVCfaced washable board for side and roof linings. The window cappings are glassfibre mouldings trimmed in walnutfinished Flex i ne.
At the front, a large glass-fibre moulding is used for the entire facia assembly, with the Thames Trader instrument panel transferred to it. The original dash structure supplied on the chassis is discarded.
When the 4D diesel engine started from cold, an appreciable amount of vibration was noted. This diminished somewhat as the unit warmed up, but the characteristic tendency of this engine to be noticeably more rough-running at low and high speeds than in the intermediate range remained evident. As with previous passenger conversions of goods chassis fitted with four-cylinder diesels, it seemed likely that the engine mountings were unnecessarily hard for this type of work, allowing vibration to be transmitted rather than absorbed.
The demonstration vehicle was, however, fitted with an Eaton 1350-series twospeed axle and, in the hands of a driver able to exploit it to the full, it Was possible to avoid use of the rougher ranges of engine speed to a considerable extent, The Kenex works driver was particularly adept at this, and invariably made " split " changes from the high ratio of one speed to the low one of the next, or vice versa.
Driven in this way, the coach had a good performance, as the combinations of gearbox and axle ratios were unusually evenly graded. The transmission could, in fact, be treated as if a close-ratio eightspeed gearbox were fitted. Except for that between first high and second low, none of the ratio steps was wider than that of 1.39 to 1 between the high (4.5 to 1) and low (6.25 to 1) ratios of the axle. The actual overall ratios given were 40.4, 29.1, 19.3. 13.9, 10.55, 7.6, 6.25 and 4.5 to 1.
The noise level in the demonstration coach varied somewhat, depending not only on how hard the engine was working but also on the position within the body from which it was noted. Moving forward up the gangway when the vehicle was travelling, one noticed that a sharp increase in noiseNoccurred on passing the doorway, apparently because of some echo effect. It is likely that production coaches will be appreciably quieter, however, as additional sound insulation is to be built in, whilst the moquettefinished engine cover available at small extra cost may also prove beneficial in this respect.
Laminaire variable-rate rear suspension was also a feature of the vehicle tested. This gave an acceptably soft ride, but a rough road near the Kenex works revealed the need for darnping when few passengers are being carried. One or two minor rattles could be heard under these conditions, but this was entirely excusable c12 as I was informed that the vehicle had been driven at speed over the Ford rough track without revealing any more serious faults and without subsequent attention.
The steering column was more upright than on the standard Trader, and when I drove the vehicle for a few miles it seemed that this modification had been slightly overdone. 1 found it difficult to avoid sitting rather too far back from the wheel if one's feet were to be comfortable in relation to the pedals. Some regular drivers of forward-control vehicles appear to prefer to sit well back and this is perhaps partly a matter of taste.
My spell at the wheel coincided with a heavy shower and the vehicle felt very surefooted on wet roads despite the fact that only three people were on board. An appreciable understeer effect on main road bends was noted, and the extra movement of the wheel found necessary because of this seemed to require slightly more conscious effort than 1 associated with this model. This may have indicated no more than a need for greasing, or it may have been due to the driving position mentioned in the last paragraph. The windscreen wiper layout caused the view of oncoming traffic to remain partially obscured by rain drops.
Despite being less practised in the technique of using the two-speed axle control and gear lever together than the Kenex driver, I found the road performance good. Speedometer readings of 50 m.p.h. came up without any impression of effort, and the close-ratio transmission meant that a suitable ratio could be found for any hill. This enabled the output of the 4D to be used to good effect. A useful gain in fuel economy should result from intelligent use of the two-speed axle, and its extra cost appears to be a worth-while investment.
At £2,989 10s. for the basic diesel model, much the same could be said for the complete vehicle..