"RUNNING IN."

Auckland Star, Volume LVI, Issue 184, 6 August 1925, Page 15 (Supplement)

"RUNNING IN."

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| HUMOURING THE NEW CAR. S ITS VIRTUES EXPLAINED. j THE FIRST 500 MILES. te Everyone should know that the brand * new car requires rather special treat- ■ tm-nt, and that what is good and fair for i the car that has covered its first thou- ■ sand miles may prove disastrous to the !■** car that has just left the factory. Makers and agents rightly impress upon buyers the importance of their advice on this subject. Nevertheless many buyers, and often owners who have owned and driven ears before, are inclined to disregard these well-known precepts. 3 The First 500 Miles. R .... _*. there are many good reasons, howjf ever, for observing the restrictive rul__j illga not lo exceed 25 or 30 miles per iiour for the first 000 miles. This applies especially to cars that are built down V to a price—and the great majority of cars that are imported into this T country are of that nature. It is not . meant by this that the workmanship — has been unduly skimped, the cars made _ of poor materia], or anything of that ~ nature, but simply a rule for vehicles that have not been built with disregard of the expense. In the latter class of T vehicle every part, even to the most L minute, is tested to give the highest ▼ degree of efficiency, and is rejected if, in the expert and acid test applied, there is ' tho slightest variation from the standard. In mass production there cannot be this same degree of exacting care to V detail, and it is in consequence that makers lay down the principle that the ™ breaking in must be according to given . rulings. Their observance will amply ™ repay the owner in the subsequent life hi of tho car. » A Football Simile. Provided that the owner be a man of C careful and intelligent disposition, he may conduct the preliminary "runningy in" of his car just as well as the manufac(rt turer. He must realise that, as he has not paid the manufacturer to do it for ' ' him he must be prepared to do it him--1 X self. The need for this running-in pro- < i cess may be explained popularly, and it i X may be explained technically. The popular explanation may be best conveyed by a•' simile. Every individual member of ' N a football team may, be an absolutely I > iirst-class player, yet the team i as a II whole cannot give of its best until its

members have played together many times and learnt the subtle art of combination. How many times has a team of. first-class individuals.been beaten by: a team of second-class men simply because the latter knew each 'other, whereas the former were playing without any complete idea of each other's capabilities and weaknesses. So; until the parts-' of :a motor car have had time, to settle down to harmonious working together,: the car cannot give of anything like its utmost capabilities. And if that Settling down, or running-in process, be unduly forced or hastened the car-will never be able to do all that it might have done. So far the parallel with human beings holds good. It fails in that the effects of forcing with humans may be remedied, but with mechanical things it can never be—except by complete reconstruction of the car, which, of course, is out of the question. Bearings and Bearing Pressures. The technical explanation is more informative. It turns on what are known as bearing pressures. Quite apart from tho bearings usually and properly so-called, the motor car contains a mass of bearings which are often not recognised as such. Of these perhaps the most important is the piston, working up and down in the cylinder. . Then there arc .the pinions engaged with others in the timing gear, in the gear box, and in the back axle (both differential and actual driving). If the timing gear is chain-driven, if the back axle has worm drive, the general truth of the bearing analogy is in no wise affected. The valve stems in their ■mides and the mounting of the chassis springs on frame and axle are two further and extreme examples of bearings that are often not recognised as such. Friction Between Bearings. No matter how carefully the surfaces of a bearing be prepared in the workshop, they can never be brought to that degree of perfect pitch which is essential for the minimum of friction between them while they are working together, or one is over .the' other. Such smoothness, both literal and metaphorical, can come only, from usage. Now,, the.stress exerted between the two surfaces of a bearing, is measured by what is known as. ! the bearing pressure, and every bearing pressure throughout a car is determined by the throttle opening of the engine. JiJlJi^_J_yjf#JJ-t-l-*-*e

Mere speed ias such, and except as applied to the road wheels and chassis springs, is of secondary importance. What does matter is the load imposed on the bearings. • If a pair of pinions be designed to transmit a torque ofr say, 501b or 5001b, feet, .if an engine bearing be designed to withstand a pressure ol 15001b per square inch, if a road spring mounting be designed a stand a shock of half a ton delivered in the form of a blow at forty miles per hour —if these things be called upon to take their maxima before they have settled down, and, as it were, given time to realise what they must be prepared for. th»v may not be broken, but they may be badly strained.

Speed and Load. Excessive friction between two bearing surfaces will cause the beginning of wear that will proceed at an ever-in-creasing rate, and will soon impose the need for extensive repairs. If those loads be kept down until the bearings surfaces have obtained a state approaching perfection, when they are imposed, they will be received easily and absorbed naturally, because the smoothness of the bearings will have attained a degree where friction is comparatively alight. Hence we get the very useful precept that not only Bhould the road speed of the uew car he kept down to strictly moderate limits, but also the load

imposed on engine bearings and the transmission should be even more carefully restricted by the avoidance of wide throttle opening. ' In order to provide the maximum possible cushioning medium between the bearings of a new engine and transmission system, lubricating oil thicker than that to be used at a later date may be given to the working parts,, and this in itself will impose a further need for modest speed. Similarly, the use of an upper cylinder lubricant —a high flash point oil—is to b2 commended. ' One of those special oils could be fed to the engine mixed with the fuel is always a good vhing to use, but never better with the brand new or very old car.