CYCLING AND MOTORING.

Taranaki Daily News, 5 August 1916, Page 10

CYCLING AND MOTORING.

CVLINDKI! COOIJVC, Few motorist- realise the importance anj purpo-c of cylinder cooling. The higher tin; compression pressure and tlie; smaller tin- heat lost through tin; wall of the cylinder head the higher will also he the maximum value of the explosion pressure. This occurrence, almost intuitively anticipated hv engineers, is fully verified by actual experience, and photographic diagraphs—the only reliable evidence in connection with highspeed engines—show that with other conditions unaltered the highest pressure and temperature invariably obtain for the least intensive cooling of the combustion chamber. If consecutive graphs are taken from the moment of starting—that is, when the metal is cold —until normal running is reached, it is found that the maximum pressure is comparatively low at starting and gradually increases with the temperature of the cooling water until it reaches its normal value. The obvious inference is formulated in one of the most important rules of engine design, and is often expressed by saying that the temperature of the explosion is affected by (a) the shape of the combustion chamber, (b) the ratio between its inner surface and its volume, and (c) by the degree of intensity of the cooling. The pressure of the gases causes the piston to move and gradually uncovers the cylinder 'wall. The latter is lined, as it were, by a thin film of oil distributed round the bore by the piston on its up-stroke. When the bore is being uncovered by the piston the hot gases do not immediately come into contact with the metallic wall, but with the protecting oil film.

At this moment two alternatives are possible; either the thinness of the lilm and tile chemical composition of the oil permit the film to he burnt away entirely, thus leaving the metal bare, or the film is capable of resisting the destructive action of the hot gases. In both cases, however, lubricant will be burnt; nor could it be otherwise, considering that it is in immediate contact with gases at a temperature of over '2ooodeg. F., and in an atmosphere where oxygen is not wanting. That such is the case is amply proved by the fact that every engine consumes a certain amount of lubricant per h.p. per hour. Incidentally, too, the fact emphasises the need to select carefully a lubricant of suitable viscosity and "body," recognising that as some engines develop a higher temperature normally than others, so it is necessary to suit them with a lubricant corresponding to the requiremen. The less the combustion chamber is cooled the higher will be the explosion, pressure, and, accordingly, other conditions remaining the same, the higher will be the efficiency of tjhe engine. The important factor that determines the minimum degree of cooling is the danger of pre-ignition. With the high compression pressure sometimes adopted it is a matter of difficulty to avert this danger, especially with big engines. The spherical cyliuder head undoubtedly reduces the losses during the explosion, but the surface cooled is also correspondingly smaller, while the volume of gas and, therefore, the heat developed, are the largest possible. Within the cylinder proper, however, the conditions are entirely different. In tliis case the object of the cooling is to prevent the uncovered lilm of oil between the piston and cylinder wall at any point of the stroke from being burnt away and so prevent the piston from seizing in the cylinder. Moreover, cooling has also the effect of ensuring uniformity of expansion of the metallic wall, and also Ueepes this expansion within pre-determined limits. Provided that these requirements are met, little importance attaches to the degree of intensity of cylinder cooling; since however intense it is it cannot possibly prevent the combustion of a part of the lubricant in contact with the hot gases. If the cooling effect is just sufficient to satisfy the above requirements, a larger consumption of lubricant will occur, but the efficiency of the engine will remain practically unchanged.

NEWS AXB NOTES. Rear-Admiral Sir R. K. Arbuthnot, who lost his life when the Defence went down in the great naval battle olf Jutland, was a keen racing motor cycliiit, and was the first private owner to compete in the classic Tourist Trophy motor cycle race in England. He competed with success on Brooklands and in numerous hill climbs, reliability trials, etc. The straits to which Germany is reduced are shown by a recent order forbidding the use of bicycles for sport or pleasure in Uerlin and tW province of Brandenburg. The penalty for a breach of this order is a line of C 75 or imprisonment for one year, so the authorities evidently regard the "offence" as extremely serious. Their object, ostensibly, is to conserve the supply of rubber for war pur-poses, but it is curious that those who already possess tyres are not even permitted to wear them out—a circumstance that has already led to a strong protest in the German tress.

The cheapness of the bicycle has done much to popularise the pastime, and we should not care to return to the days when £2"2 was a common price for a machine and £3O not unusual. Nevertheless, even cheapness can be overdone, and the tendency in recent years has been for cyclists' to pay too little for their bicycie*. The war is helping to correct this, but not in quite tile best way. Cyclists should be educated to believe that a high-grade machine is the best bargain—that it will give far greater all-round satisfaction than any lowpriced mount; that it means a higher standard of pleasure, a keener delight in the game.

What is the future of the motor-car wheel? From many point of view (says the Jlotor), the wire wheel is the best detachable. Closely following this type in popularity comes the steel wheel. In each caso the disc covering is showing signs of increased popularity. From the point of view of service, the disc covering is all that could be desired. It removes the one and only defect of the wire wheel, namely, the difficulty of cleaning. From the appearance point oi view, however, it is wholly abhorrent. The wire wheel itself is of pleasing and mechanical appearance. Put an ugly black disc on it, however, and it becomes exactly the reverse. Is it quite impracticable to combine the two good features, without,- the dei'eet No one appears to have tried. Is it, then,' impossible to get souk: sort of colorless and transparent disc? if some such disc could be made practicable one would forthwith have the very useful advantage of the disc cover, and at the same time retain the distinctive appearance of the wire or steel wheel.