Mr. C. M. Linley's Show Impressions .
Page 19
If you've noticed an error in this article please click here to report it so we can fix it.
Comments on " Lessons from the Show."
Crankshafts and Camshafts.
The Milnes-Daimler is pointed out as being particularly practical, on account of its having the tuning gears mounted in the middle of the engine. I consider this point to be one that is open to diecussion. The points stated in favour of this arrangement are that it gives a neat appearance to the engine, allows four bearings to be fitted, and relieves the camshaft of torsional strain. I will grant that it makes the engine look neat, but cannot see how the two beatings in the centre and the gap between them improve the engine. If longer bearing surfaces are required in the middle, why not make a longer bearing? It would be cheaper and easier to fit. The lengthening of this part of the crankshaft might be condemned, by the same argument that is used in favour of the airangement, when applied to the camshaft. The shorter the crankshaft within reason, the stiller and better it is. I cannot follow the argument of " Builder " re lag of camshaft. The torsional strain on a camshaft is only small, and there is no need to cut the camshaft so fine as to expect any lag. I think the want of accessibility of this arrangement outweighs any of its good points. if it has any, and I do not expect to see it become popular.
Cylinders.
With regard to cylinders cast en bloc, this certainly makes an engine look smart ; but, for commercial work, I see a good many reasons why it may not become general. it must always be remembered that a commercial vehicle, although a delicate and complicated piece of machinery, has to be used often by persons whose experience and intelligence are very limited. It is difficult to make such persons realize the importance of emptying cylinders in frosty weather. It is also difficult to make them see the harm that may he done by running short of water, and filling up with cold water when hot. In the case of such mishaps, which are not unknown, the cost of renewal is against the en-bloc type. I have heard experienced van owners speak in favour of separate cylinders for this reason. Another point against the en-bloc type is that, unless the casting is unnecessarily long, it is hard to find room for a centre bearing of sufficient length to be efficient.
Rear Axles T quite agree with " Chief Draughtsman " that the rear axle is a subject of absorbing interest to designers. Bevel gears alone, although shown, can only be used on the lighter models, as it is impossible to get the reduction required for a commercial vehicle and still preserve a good proportion for the pinion. Chains undoubtedly have their good points ; one is that they allow of great ground clearance, which is so valuable in the Colonies and certain other parts of the world. I do not consider the employment of a silent chain inside a chain-criee to be an advance, nor do I consider it necessary. The roller chain becomes perfectly silent, when used inside a complete chain-ease (not a chain guard), and it is generally admitted that the roller chain will better accommodate itself to sprockets that are out of line than will the silent type. That the double-reduction type will be very largely used I feel sure, but I cannot agree with. " Chief Draughtsman "when he says that it is good for service abroad. In the form shown on most of the models at Olympia, there was not enough ground clearance to satisfy some foreign buyers. I know of many parts of the world where a. 12 in. clearance is not enough. Some structural alterations will have to be made in the double-reduction types before they will be useful abroad. There is one thing that "Chief Draughtsman" says that I cannot follow. He speaks of adjustment in the bevels " for wear." I have seen workshop adjustments provided for, but I cannot see how bevel wheels can be adjusted to take up wear. Surely, the altering of the depth of engagement, after its once having been correctlyestablished, can do no good.
Double-reduction Alternatives.
When a designer starts on a double-reduction axle, he is bewildered by the number of ways this design can be carried out. There are five distinct and separate types of double-reduction back axle. He has also a great many choices of materials. It may be cast, partly cast and partly forged, or forged throughout. Personally, I think the latter is the axle of the future. Then, again, there are the burning questions of torque rods or no torque rods, radius rods or tube, one or two universal joints, etc. One could argue the good and bad points of the various systems for a month, so it will be seen that the designer's lot, when engaged on back axles, is not a happy one.
"Chief Draughteman " takes a general survey of the Show, giving the numbers of the different types of drives. Such figures are not of much use as an augury of the future. There may be a hundred of one model shown and only one of another, yet that one may stand out clearly as a signpost pointing the way.
Ignition.
" Expert " notices that on one model shown the leads were coloured. This is by no means new, as a leading firm has made a practice of it for the last seven years. It is of the greatest value to drivers who are not very familiar with wiring, and saves a lot of time when taking down and putting up again ; it is curious that ithas not been more copied.
I quite agree with " Expert " in his remarks re switches. The switch suitable for commercial work does not seem to have been made yet. Most makers would fit better switches if they could procure them. With regard to a connection between switch and throttle, these sort of connections look very nice at a Show, but are seldom feund to be useful in actual practice: In time, they are mostly removed owing to the development of sonic trouble which the designer did not foresee. C. M. LINLEY.