Design for Maintenance.
Page 7
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Always insistent upon the importance of the designer's familiarizing himself with every possible detail of the necessities of operation, we willingly give publicity to the short article which follows—from the pen of a maintenance engineer of considerable reputation—with a view once more to the enlightenment of the designer as to the needs of the maintainer.
By a Practical Engineer.
As an engineer responsible for the running and upkeep of 34 motorbuses and 8 steam lorries, I often feel constrained to ask the question, when is the maintenance engineer to receive a little more consuleration from the designers of commercial motors'? I do not ask this question in any carping spirit, but with the genuine intention of bringing under the notice of designers of commercial motors some of the points they should adopt and some they should avoid, if they want the machines they design to continue in favour with those who may purchase them.
Design for Continuous High-rate Performance.
in some cases it would appear as if the designer had not considered the question of maintenance at all, or if he has, then be has made repairs and renewals as awkward and expensive as possible. Designers ought always to keep in mind that it is not sufficient to design a machine that will do certain work, but it must be designed so flint it will be capable of going on doing this work for a reasonable time. When certain parts have become so worn that they have to be repaired or replaced, provision should be made in the design for these repairs and replacements being done as quickly and cheaply as possible.
Carefully-concealed Valve Tappets.
Some of the machines I have, to keep in running order afford excellent examples of what to adopt and e hat to avoid. On some of them it is not, possible to get a valve tappet withdrawn for examination or iepairs without first taking down the induction, exhaust and water pipes, and lifting the eyliixlers. These tappets are not adjustable ; hence, the full life can only be got out of the valves by piecing the stems, which at best can only be looked upon as a makeshift.
In a great many machines the clutches are so designed that, before the cones can be taken out, relined and put back again, a whole day is occupied on the job. With A, properly designed clutch it ought to he possible to do this in three hours at the most. Clutches should have two flanges for the lining fitting in between, in order to prevent it from being easily torn off.
Big-ends that are Inaccessible.
it is by no means difficult to get instances where the whole engine has to be taken adrift before it can be seen what state the big-ends are in, and the same general remark applies to gearboxes. It should not he a difficult matter to arrange for inspection holes on the sides of crank-cases, or better still the bottom. of the case should be made so that it can be removed without interfering with the main bearings. [Practically all recent models have.—En.1 It is a simple matter to have doors on the tops of gearboxes large enough to admit of the whole contents being seen at a glance.
Wheels and Brakes as One.
In some instances which have recently come under my notice steel driving wheels have been employed where the wheels and brake drams are cast in a single piece, with the result that when the brake drums become too thin the wheels will have to be scrapped. In connection with brakes it may be said that they are generally designed so that the whole bloc, which is a rather expensive casting, has to be scrapped when the rubbing surface is done, or if designed so that the blocks can be Kelined, the linings are fixed in such a way that a great deal of time has to be spent fixing on the new linings. Brakes should be designed so that the blocks can be relined, but the linings should be capable of being quickly and at the same time securely fixed.
Must Get Your Hand in Tanks.
As a rule pet),ol,tanks are made so that the only opening into%them.eambe closed by a cap about two inches in diameter. All sorts of oddments have a nasty habit of getting in at an opening of this kind, but unfortunately they are not very easily got out again, consequently petrol tanks should have doors on the top large enough to admit a man's hand and arm.
Unreliable Aluminium.
There seems to be a growing tendency on the part of designers to use aluminium. It is now being extensively used for engine erank-easesi gearboxes, etc., but from the maintenance engineer s point of view, aluminium.has very little to recommend it apart from its lightness. It does all right for cases or covers on which. there is absolutely no strain, but for parts whict are subjected to stresses or strains it is too ductile, so that-distortion easily takes place. When used, for caank-eases or gearboxes which have to carry bearings, the bushes or bull bearings quickly become so slack in their beds or housings that the aluminium casing has to be scrapped.
Fork joints for brakes and steering gear are other examples which might receive a little more attention. Plain pins are very often put into these joints so that they ean'turn about at will. All pins should be fixtures in the forks, and the eyes should be bushed to begin with ; the bushes should preferably be case-. hardened. It would then be a simple matter to replace pins and bushes and thereby to put theejoints into the same condition as they were in when the machine was turned out by the builders.
The Man in Charge Makes or Mars the Machine's Reputation.
Ineconclusion, I might just say that it is the amount of attention bestowed upon small details Such as I have mentioned that makes the machine a favourite or otherwise with the-maintenance engineer. I think there cannot be two opinions about the maintenance engineer's being the man who can ultimately make or mar the success of any machine. His opinions are therefore entitled to the careful consideration of those who design new models, but who. I fear, very frequently do not acquaint themselves with the little troubles which ensue when the vehicles pass into actual hard service.