THURSDAY, NOVEMBER 27, 1930.
THE CHINA MAIL.
PISTON TROUBLES & THEIR CAUSES. heard when the cold engine is start-
or
MU
A
time д Piston troubles,
least in the same period of obvious ones, ure, considering the tremendous advance has been made light weight of the modern piston in the power obtained from and the speed at which it travels, cylinder of given size. comparatively rare, but with a cer tain amount of care in driving and in watching the lubrication even the few cases which come to notice can be eliminated or at least con siderably reduced.
Manufacturing methods of the present day have developed to such high standard that a faulty plston is almost unknown, and, we must, therefore, look to the driver of the car to keep these hard-worked units at their normal operating efficiency, Being tucked away inside the en- gine, the pistons are rarely seen, and because of this few drivers give them more than a passing thought. An idea of what they have to perform may serve to bring to light a few reasons as to why these parts of the engine should have considerate attention. Speak ing broadly, the piston is the hard- est-worked part of the motor. It is thrown up and down. violently pushed and pulled by the forces produced by the explosions and by its own inertia, heated by flaming gases, and forced to rub against the cylinder wails by a heavy side pros- sure. Under these conditions it covers a surprisingly big mileage, so that when the has done 10,000 miles each piston has travel led in the vicinity of 5,000 miles up and down in the cylinder. Con- sidering the load which it carries, its difficult duties 57 preventing gas from escaping down into the crank- case, and oil. from passing up Into the combustion chamber, and the very great difficulty of lubricating sliding surfaces subjected to high temperatures, the average piston performs its work with a marked amount of success.
car
Aluminium Pistons. There is a marked tendency on the part of many drivers to ascribe all piston troubles which have occurred during recent years to the change
from cast iron to aluminium alloy. Those who think on these lines are apt to forget that
over
An Increase in power can be ab- tained in two ways, both of which fully used. The have been very first consists of increasing the com- ression ratio. and the second of increasing the engine speed, or, to put it plainly, increasing the power of the explosion and getting more explosions per minute. It must be obvious that this development re- sults in a twofold increase in the load carried by the piston. First, there is a direct increase due to the higher gas pressures and to the higher temperatures, and there is the increased inertia load caused by the higher speeds. A piston must be stopped and restarted at the end of every stroke, and this requires very big forces, often amounting to over a ton when the engine is turn Ing over at high revs. To meet the situation, and to bring the loads carried by the bearings inside rea- sonable limits, designers have been forced to reduce the weight of the piston as much as possible.
Troubles.
the troubles Getting back to which have been experienced with pistons in heavily-louded engines, these may be divided into three classes-piston slap, rapid wear, and heavy all consumption. Before in which an describing the ways owner can safeguard the pistons, It would perhaps be as well to consider these troubles and their causes.
ed after a slight aniount of wear has taken place. This has been remedied to a large extent by the ase of Invar Strut pistons, which allow of a comparatively close fit. Next, there is the big subject of platen lubrication. The oil which the cylinders receive is almost! wholly derived from the spray or mist produced by the big ends. The the lubricant to the pump feeda
the all travels crankshaft, and through the passages in the shaft to the big end bearings. The sur- plus escapes from the ends of these bearings and is thrown round by the whirling action of the shaft, so becoming deposited upon the ex- posed lower surfaces of the cylinder walls.
The platan in moving up and down obtains its fubrication by picking up oil deposited in this way. It is essential that it should receive sufficient lubricant; oil is cheaper new pistons and reground than cylinder blocks. On the other hand, only a very slight excess is needed to make the difference between a reasonable oil consumption and one open to criticism as being too heavy.
Piston rings are, of course, pro- vided to hold the compressed gases and also to prevent oil pumping many pistons having special oil rings to control the amount of oil upper part of the reaching, the piston.
This scheme works well enough so long as the rings at closely in their grooves, but when a certain amount of up and down play develops a pumping action takes to a rapid in- place, which leads crease in oll consumption. All ordinary metals expand when This is one of the most important they are subjekced to heat, and the causes of high oil consumption, the rate of expansion is greater for all being delivered to the combus- aluminium alloya than it is for cast tlon chamber, where it is burnt. The pumping pressure which the iron. Consequently, in order to prevent a piston from acizing while rings develop is surprisingly high, hot the clearance between the skirt and consequently, contrary to popu- and the cylinder wall when the en-lar belief, the pressure above the gine is cold must be in the vicinity piston is not of much moment. In of .005in. In a cylinder with a bore other words, the amount of oll burnt of about three inches. It is well when the engine runs at full throt- known that an audible tap is pro- tle is almost as great as when the Is closed, and when duced if the clearance gets in excess throttle
suction 18 de- of .003 in., so that it will be seen considerable
оп the inlet stroke that it is exceedingly difficult to veloped
it is prevent such a top from
popularly supposed to
being
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OWNERS
OF
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MOTOR CARS
IN CASE YOU DO NOT KNOW WE BEG TO
INFORM YOU THAT WE MAINTAIN
A SERVICE DEPARTMENT
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CONSULT US IF YOU HAVE BRAKE TROUBLES
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DES VOEUX ROAD CENTRAL
TELEPHONE 25640
THE
खे
u'
"I never thought it possible for a car to travel so fast, and yet pull up so quickly and gently."
"Well, Sir, Buick had a 25-year reputation to maintain when it built this eight in a line and had to keep faith with those tens of thousands of people who buy Buicks year after year because of their confidence in Buick's performance."
new Buick is characteristically Buick in all those qualities which have contributed so materially to Buick leadership for a quarter of a century,
2
Bulck has won public confidence on the sheer merit of its. products year after year. Thousands of motor car buyers buy Buicks without even asking for a demonstration.
The new Buick, in all series, reflects -- even more than any previous Buick has the supreme value for the money that only an organisation like Buick and General Motors could possibly give.
Why not let us demonstrate the new Bulck to you to-day ?
The
BUICK 8
THE DRAGON MOTOR CAR CO., LTD.
Telephone 30228.
33, WONG NEI CHUNG ROAD, HAPPY VALLEY.
It
assist all to pass the rings. is true that the characteristic blue amoke disappears under full throttle conditions, but this is mainly duo to the fact that the cylinder tem- peratures are then sufficiently high to burn the oil.
Apart from wear of the rings and grooves, there is the general wear, which gradually makes a piston a slacker and slacker it in the cylinder. With cast-iron pistons this wear is more or less confined to the area that is awept by the rings, but in an aluminium piston wear occurs throughout the stroke. It is, however, mainly the relatively tough cast-iron cylinder which suf- fers, very little change occurring in the size of the piston.
How Platons Are Ill-Treated. There are many ways in which the owner-driver can ill-treat the pistons of his engine. In the first place, very few people take suffi- clent care over the essential process of running-in a new engine. takes quite an appreciable time to produce a good working finish on the rubbing surfaces of the pistons and cylinders, and, until this is obtained, overdriving is bound to harm the parts, even if it does not actually cause seizure. If the en gine gets anywhere near the seizing point the aluminium becomes very soft and is apt to be badly scored, or rubbed, sa tending to fix the rings in their grooves, and, of course, to ruin the bearing surface. Next there is the matter of lubrication. In a new car the big ends it so tightly that the ol escaping from them is not quite as much as is required for fast work. It Is, therefore, a good plan to add a little lubricating all to the feel when the engine is new. This oll la fed through the carburettor, and effectively alds the lubrication of the upper parts of the platon and cylindera. Supposing that a car has been run in with due care, there remains the duty of giving the platous a chance to prove durable. By far the most common form of Ull-treatment consists of starting the cold engine and fore ing
It to propel the car. It' cannot be tea strongly. emphasised that this procedure may cause as much.
→Venr
it is made to drive the car the parts will become heavily loaded, and the rate of wear is naturally vary great, indeed.
J
CAR DESIGN.
New Features in 35 Years.
The Eights with Buick's Prestige
Perhaps the most interesting part of Sir Herbert's address was that dealing with weight reduc- tion. It was suggested that the A minor point, but one well worth
road vehicle of the future will remembering, is that, in addition
have many leas: parts, and al- to draining and refilling the sump.
though automobile.engineers will it is as well to have it entirely re-
be in general agreement that this moved, say, every six months, so
Is an ideal to be aimed at, it is that every particle of sludge may The development of the touring difficult to foresee how it can be be removed. Air cleaners and oll car may be said to have commenc achieved. The chief point made. purifiers are, of course, of greated about 1880, when the petrol by Sir Herbert was that the con- service in preventing rapid con- engine first became a commerciai struction of the body and chassis tamination of the lubricant.
success, although it was not until na practically independent units and Another kind of misuse cau best after the repaul of the Locom resulted in redundant parts be described as overdriving. Antives on Highways Act in 1896 needless weight, but this point bas engine shaald. be treated with a that the construction of such cars certainly not. been overlooked by reasonable amount of consideration. was taken up seriously in Britain. manufacturers, and the fact that Unduly high speeds in the later Some of the earlier cars had the so little has been achieved is suffi- mediate gears produce excessive major components arranged in the clent indication that the problem leads on the reciprocating parts, sequence:--radiator, engine, clutch, is very difficult of solution. The and, of there, the pistons suffer gear box, propeller shaft, and rear greatest difficulty in designing a most...
axe, the final transmission and the frame which shall serve to house High Oil Consumption. differential both being of the bevel both the body and chassis com- The causes of high oll con- type. The gear box Incorporated ponents la presented by the break sumption after the engine has been two or three ratios with clash en-in continuity. represented by the In service for some time should be gagement; Ackermann steering was doors, but the loss of accessibility fairly obvious... Wear will have employed, and the chassis was car is also likely to be serious. It is increased the working clearance of ried on semi-elliptic springs fore and only necessary to imagine the in-
of undertaking the big ends, so that a relatively aft. It is decidedly striking that convenience large amount of all is thrown up this layout has withstood the test of chassis overhaul without taking into the cylinders; wear of the time so successfully that the details off the body to appreciate the diff
outline culty that the designer would have rings in their grooves, and of the given would serve as an cylinder bores will render these specification for the majority of to overcome. As regards weight, parts incapable of preventing much modern cars. In his Presidential reduction in other directions, we of this oll being pumped up into Address to the Institution of Auto- huve previously expressed the the combustion chambers.
mobile Engineera, Sir Herbert Aus- view that chassis. frames could ba When the rate of ofl consumption tin enumerated a number of addi- made very appreciably lighter at shows a noticeable increase, it is tional features which have charac-only a slight increase in cost by not at all a bad plan to have the terised design during the past employing open side members, sump removed and the big ends thirty-five years, and suggested that that is, members of greater depth takon up. This alone may check the adherence of modern manufac❘ with the majority of the web the oil consumption for some time, turers to the conventional layout punched out, leaving only isolat- but eventually it will be necessary given above was due to stabilisation ed bridgea between the top, and to have the cylinders re-bored and of design, made necessary by, or bottom flanges. Woight reduction new platone and rings fitted. Or consequent upon, mass production by the employment of wire wheels,. course, If examination shows that to obtain a low manufacturing cost. high-speed engines, steel stamp- the piston clearances are not ex- It may be pointed out, however, ings, and light aluminium alloys, cessive, it may be sufficient to fit that the Influence of this factor has has been practised to a greater or new rings, Including a scraper ring only become preponderant in the lesser extent for many years, and of one of the many designs now last few years, and that there has it is not easy to see that the ap consequently been a considerable plication of such devices on a available.
period in which designers had free greatly increased scale is possible dom to develop unconventional are without an increase in cost, which, rangements. This freedom has, in when all is said and done, is the fact, been exercised from time to controlling factor in designing time, but with one or two striking for a large-market-Engineering. exceptions, a return has always been
LIGHTEST METAL.
Motor Bearings That Will Not Wear Out.
Motor cars with bearings which
Since 1920 no Journal, with the single exception of The Motor, has attempted to produce and publish in one ferue a complete, alphabetical report of the Show, classified In many sections, and covering every exhibitor's stand.
made to the conventional layout. It therefore appears rather more likely A COMPLETE SHOW REPORT. that the pioneers were gifted with very considerable acumen, and that the arrangement adopted by them is, as, perhaps, 500 miles of ordinary running on the read. When the will not wear out may be placed on upon the whole the best that can be. engine is cold, particularly in the the market in the near future as the devised for a vehicle to meet the winter, the oil is sluggish, and it result of the discovery of large needs of the ordinary Individual may be as long as half a thinute deposts of lithium in South-West Such a vehicle is essentially a com promise between first cost, running before any reasonable quantity is Africa, Dr thrown off the big ends. During Lithium a the lightest metal costs, and accessibility, and it need this period the platons, with the known, and has a specific gravity of not he suggested that the conven-
The number contains" about 132 stiffscraper rings have rapidly not much more than half that, of tional arrangement is necessarily the removed most of the oil from the water. It is understood to be the best if some unusual feature, such pages of reading matter and the cylinder walls, a process which is chief element in a new aluminium as ability to negotiate rough ground, announcements of practically the It con aided by the wet petrol mixture alloy which is much lighter than is to preponderate. Another factor entire notor industry, drawn in. Consequently bone dry pure aluminium and nearly as strong which it is Impossible to neglect, but stiutes such a completo guide to the pistons and rings are rubbing up s steel, and which will stand in- equally impossible to evaluate, le reader as to the trend in every. and down for about half a minute definite wear as a bearing material, that of fashion, and it must be ad- direction of the Industry, including before anything like adequate Already thousands of tons of ore mitted that dislike of the unknown this year the motor boat and garage lubrication commences. If, during have been mined, and the deposits in on the part of the public. has re- servicing Beckons, that AN this period, the engine is allowed to the mine working will not be ex-sulted in the disappearance of ence book for deca Idle, no harm will be done, but it hausted for many years,
many promising.