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A T the Commercial Motor Show, which dosed only three days

17th November 1931
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Page 54, 17th November 1931 — A T the Commercial Motor Show, which dosed only three days
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ago, there was, by reason of the large number of bare chassis exhibited, a really good opportunity for the vehicle operator to study current practice, as regards both chassis for goodscarrying vehicles and those for passenger models. During the past few weeks the various Special Numbers of The Commercial Motor have contained articles dealing with all the major topics of vehicle construction, so that in this article it is proposed to deal with onlydetail features which have a particular appeal to the ptirchaser, to the maintenance engineer and to those most intimately connected with the running of the vehicles on the road. Modern types of engine, as a whole, are reliable. During the past two years a marked improvement has taken place in the methods of mounting the engine so as to insulate the comparatively delicate crankcase from torsional shocks and, at the same time, to permit rapid detachment of the engine. Split front crossmembers and divided rear banjos are common practice. Great forward steps characterize the crankcase layout, in that the crankshaft bearings now have far more adequate support, and should, in consequence, have a longer life without requiring adjustment or renewal. There is, however, one point which is not nearly so universally catered for as it should be. This is the matter of far more adequate oil purification and cooling. The first cost of cooling and filtering systems is more than repaid in a few months' time. Belt drive for fans is coming back into popularity. Some operators have found that, in certain instances, the exceptionally long chains required for a positive drive are not always desirable, and repairs to or replacements of the fan belt are easy tasks calling for no dismantling of parts.

Gearbox Features Examined.

Turning to the question of the gearbox, this is now commonly mounted on the rearward face of the enginegearbox-carrying banjo, where unit construction is adopted. Good examples of this are to be seen on certain Thornycroft models. This principle obviates one of the chief bugbears of unit ctonstruction, from the maintenance engineer's point of view.

For several reasons the practice of mounting gearbox fillers directly on the casing is not always advisable. Trap doors in the floor cannot be lifted without load displacement, and modern low-level bodies often obscure the frame side members, so that replenishing the box is far from easy. In cases in which the filler of the gearbox is brought right out beyond the frame, this difficulty is largely obviated. From the point of view of reduced repair bills, there can be no two opinions as to the desirability of three bearings for each of the gear shafts. This principle is rapidly gaining ground, particularly in the case of heavier vehicles.

Another unseen but sound detail is the practice of en

providing thicker clutch facings and allowing a full range of adjustment, so as to utilize the entire practical life of the friction material. Good examples of this are found on the latest Leylands.

In general, driving axles, particularly on vehicles over 30 cwt., now have fully floating shafts, which afford certain maintenance advantages, but a striking new model which differs is the Thornycroft Daring double-decker; this has semi-floating shafts in order to obtain molly

widely spaced bearings. As these shafts are hollow, they have considerably greater strength than solid shafts; the worm shaft, also, on this vehicle is hollow and should give long life by reason of the solid " foundation " for the worm.

From the operator's paint of view there are many reasons for the adoption of an offset transmission, but Olympia revealed certain examples in which the complete transmission line, from the flywheel to the rear axle, was not straight in plan. This, surely, is not good _practice, Although the double-reduction rear axle is necessarily more complicated than a worm-driven type, its extra sturdiness is much appreciated by operators of heavy vehicles, particularly those which employ oil engines. Really stout jobs of reassuring appearance were found on the Crossley 6-tonner and the new Sentinel shaft-driven six-wheeled steamer.

. Allied to the question of transmission is that of wheels. In the past the parcelcar, particularly of the three-wheeled type, has often been handicapped by the employment of fixed wheels. It is interesting to note that the latest Raleigh vehicle embodies an ingenious system of detachability which is sure to be appreciated by users.

Quite a feature of this year's Olympia Show was the tendency to employ detachable rims in the case of vehicles with really large tyres. The main advantage from the user's. viewpoint is that wheel-retaining studs are abolished. Interesting examples of this construction were found on the larger Leylands and the new oil-engined Foden.

A pleasing feature on the Scaminell stand was the spare-wheel raising device. When a driver is singlehanded and has to effect a tyre change beside the road,. such a point as this is bound to save time—it may be even a matter of a couple of hours with a very heavy wheel.

Frame Layout Improving.

few years ago it was more or less a fashion to provide " fancy " frames for goods vehicles. This tendency is showing signs of dying out. There seems little purpose in sweeping the frame down at the dash line only to sweep it up again right over the rear axle and then down again; either the disadvantages of wheel-arches become apparent or wooden runners have to be employed to provide a uniform level on which to mount the body. Low-level frames are obviously advantageous for certain types of coachwork, but for carrying platform bodies and box-van bodies, straight frames are infinitely preferable. There are still certain chassis which have cross members rising above the level of the main frame members. This commonly complicates the bodywork construction and in few eases can it be mechanically justified.

Two years ago we remarked upon tank mountings ,which made it almost imperative to raise the body. If the tank were to be removed for repairs. To-day a great improvement is noticed in this connection. A :good example of mounting so as to permit rapid downward detachment was seen on the Halley Clansman.

As regards brakes, the evidence of the influence of Clayton Dewandre, Ltd., was seen on all hands. In addition, there were further cases of the adoption of the Lockheed hydraulic operation system; the use of external cylinders, so as to avoid overheating by proximity to the brake shoes, has a practical right to find favour with operators. A good example of this layout was to be seen on the new Dennis 3i-tonner and Lancet models. Concerning vacuum servos, the principle of employing reservoir tanks, which is almost universal on oilenglned vehicles, has much to recommend it. A detail which operators do not .appreciate so much as designers seem to imagine is the provision of handoperated adjusting nuts for the brakes. In the case of master adjusters on heavy vehicles, it is often almost impossible to turn these "over-grown butterfly nuts" without some form of tool, and they provide a poor purchase for a large adjustable spanner—usually the tool employed. It would seem better to provide a large-diameter nut in the first case.

For the smaller vehicles there would seem to be more scope for the mechanical booster gear, as employed on Unic chassis. This system gives less time Jag than the ordinary plain mechanical operation and affords a degree of assistance which is ample for most needs; the maintenance costs are negligible.

There are still rather too many chassis which have brake cross-shafts set too far away from the anchorage points of the springs, so that the radii of the front portions of the springs and those of the brake rods do not so nearly coincide as is desirable, with the result that brake "snatch" is occasioned.

During the past two years practically all passengercarrying chassis have been produced with springdamping devices. These have had a definite effect, but there are few instances—particularly in the case of passenger vehicles—in which provision is made for automatic spring adjustment to meet the load—which may vary between 3 cwt. and about 4 tons. Noteworthy exceptions are the Bristol with its patented suspension system, and Crossley double-decker, which has progressive springs.

On the front springs of certain Leylands and the Guy Goliath the use of safety clips around the spring eyes is an interesting practical development, which should reduce the tendency to main-leaf fracture, Whilst in the former case the provision of stops at the rear ends of the front springs, to permit a homeward journey in case of spring breakage, is practical.

The new Thornycroft double-decker makes special provision in its spring design to counter braking stresses. To relieve the mounting bolts of a good deal of the stresses to which they are subjected is c34 obviously desirable, both from the designer's and maintenance engineer's points of view. This object has been attained by various ways on Leyland. Thornycroft and Scammell models, to name only three.

Whilst on the question of springing, certain coachbuilders at the Show were emphatic that the front springs of some heavy vehicles are too stiff to give the resilience required, with a result that cabs suffer from unnecessary vibration and distortion.

In 'connection with the question of cabs, although these are naturally regarded as part of the body, their design is, in many cases, complementary to that of the chassis, particularly where forward control is employed. There are to-day only a few instances in which positive under-bonnet ventilation has been adopted. As a rule, the air forced backwards by the fan finds its exit in too haphazard a manner, and the result is that a proportion of the foul air leaks into the cab. On the Dennis Lance this ventilation problem has been tackled in earnest, whilst the oil-engineci Fowlers reveal a practical grasp of the situation.

Wings are much as they have always been. A flexible hind quarter, found on a Northern Counties body, gives rise to the hope that a similar form of construction may, before long, be adopted for wings, which are always so vulnerable a part of a vehicle. That they may also be made quickly detachable to enhance accessibility is another hope which should not long be deferre& In the case of the Garner, its special pivotal mounting for the front wings is, of

course, retained. By this system forward-control vehicles are made more accessible than many normalcontrol types.

Turning now to miscellaneous details, one of the general improvements of recent years has been the grouping of lubrication points. In the case of passenger vehicles these batteries are usually accessible from within the body, but in the case of a laden goods vehicle or one having a body mounted low upon the frame the story is a very different one. All greasegun points should be located so that they can •be reached without crawling under the chassis.

As regards electrical wiring, the M.C.L. system of leads in a flexible casing below the facia, clipped to the steering column, is appreciated by practical men.

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