UNSEEN BUT BUSY

Evening Post, Volume CVIII, Issue 24, 27 July 1929, Page 26

UNSEEN BUT BUSY

THE ENGINE PISTONS

There are many interesting phases in connection with the modern automobile with which the motoring public is quite unfamiliar. It has been pointed out, for instance, that the piston, of an automobile engine is one of the most active and important little parts of the car. For every mile that the average sixcylinder car runs, the pistons have to trave' more than two and one-half times as they slide up and down inside the cylinders. Eacli piston momentarily starts and stops some (3000 times for every mile an automobile is driven. In tho earlier days all pistons were made of east iron, which Lad desirable qualities with the exception of weight. Heavy metal required heavy parts with which to operate. This in turn meant more power and greater petrol consumption in order to lift the heavy piston up and down iv its constant high-speed travelling. So thoughts were turned to lighter metals in an effort to reduce weight without affecting efficiency. After years of constant experimentation, a new light alloy for pistons was developed that would greatly reduce weight and at the same time maintain a high rate of heat conductivity, which is essential to efficient motor performance. The objection to some of the earlier efforts in connection with light alloy pistons was their great expansion under heat, which made necessary a piston clearance that was too extreme and therefore impractical. At this stage of experiments, struts were introduced. These are backbones or braces of special alloy steel struts, which are cast in and become an integral part of the piston permanently anchored in place. The advantage of this will be noted when it is^ explained that this type of design scientifically controls expansion and contraction. In other words, the modern light alloy steel backbone piston has all the advantages of the old type of cast-iron piston without its disadvantage, weight. Expansion and contraction are now so perfectly controlled that a much bettor fit of pistons to the cylinder walls 'is possible. Thus'the modern motor is made to operate with infinitely more efficiency, and much of the remarkable acceleration which one enjoys to-day in a motor-car is due to this new development of the light alloy piston.