From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Page from a publication featuring letters discussing the merits of long versus short stroke engines.
| Identifier | ExFiles\Box 33\4\ Scan001 | |
| Date | 23th November 1912 | |
| H.R. 525A (500 H) (S.A. 453. 4-5-15) G.{Mr Griffiths - Chief Accountant / Mr Gnapp} 0670. LONG AND SHORT STROKE ENGINES. [18305.]—You devote the whole of your leading article in The Autocar for November 9th to the “pros” and “cons” of the long stroke engine, and yet you cannot come to any conclusion, and leave the world in general none the wiser for your expert explanations. As a driver of eight years’ experience, and who has had six cars for his experience, let me tell you that the long stroke engine is a fraud and a delusion. The whole trend of motor engine design was destroyed by the idiotic regulations for the settlement of the motor car tax. To save a paltry two guineas a year the public have had foisted on them an engine which is only meant for putting up records at Brooklands. The small bore engine with a long stroke is, in plain language, a freak. It is extremely efficient if it is made, as it usually is, with a very high compression and is run at high speed, and that is why it is lit purely and simply for sporting purposes, as at Brooklands, or for the unpleasant young scorchers who spoil the road for the ordinary user. But for the vast majority of car owners, whether they drive themselves or have a paid driver, these long stroke engines are a crass failure. One point alone should condemn them, viz., the fact that the piston heads get carbonised so soon that either the car has to be given over to the shop for several days, which means no car if your own man is to do the cleaning; or, if sent to the shops, then the bill for one cleaning will pay the tax several years running, and what is more, this cleaning must be done two or three times a year if your mileage is at all what most cars run during a twelvemonth. Granted that the oxygen process of cleaning may be no great expense, still no discreet owner will let his car be cleaned by any process except that of opening up the engine, unless he is driven for a time to part with his car. Again, most long stroke engines are on the monobloc system. This at once makes the cleaning of the piston heads a two-man business, which increases the expense. Most makers put too heavy bodies on these toy-like engines, so that after a very short period on the road they have to drop to lower than top speeds if any comfort in traffic is to be obtained. Then up goes the petrol bill. Where, then, is the economy? The only engine which can be cleaned with ease and little expense is the Daimler engine, but on this engine carbonisation causes no difficulties, owing to its concave piston head. To refer to another aspect, all the motor writers to the press make the mistake of always alluding to the “sport” of motoring. Now that idea is exploded. The Brooklands track is the only place where the sport of motoring takes place. Of the 70,000 or more cars registered in London, how many run on the track at Brooklands? Motoring is now a business proposition with every owner of a motor car. The well-to-do keep motors, as they no longer keep horses. Every professional man keeps a motor for his business and not for sport. It is quite silly this perpetual allusion to the “sport” of motoring. This word is only applicable to quite a small number of people. Whilst the disgusting behaviour of the police in this country is allowed to continue, how can you talk of the sport of motoring, except on private roads? Again, whilst the letter of the law as to twenty miles per hour is so rigidly enforced, what is the good of buying cars that can travel thirty, forty and fifty miles per hour, let alone ninety and hundred miles per hour that the freak long stroke engines boast of? Poor men who drive over twenty-four miles per hour are robbed by ignorant ill-tempered magistrates of large sums of money in lines for purely technical offences, while these same magistrates let off with paltry lines, or merely a caution, heinous offenders, and the well-to-do are disgusted at being treated as criminals by the low class methods of the police, both on the road and in the courts. It is a crying disgrace. These police brigands ought to be hounded off the roads by some means. In the crowded streets of London the police let every motor ’bus travel at 25% to 60% over the legal limit of twelve miles per hour, and yet hundreds of the force are on special duty waylaying innocent drivers on perfectly safe roads for trifling excesses of the legal limit. If English motor engineers had only devoted their energies and brains to designing engines of greater bore, and shorter stroke with easier compression, and would prevent these engines going above a fairly useful speed by valve and lift design, then for an extra two or four guineas tax the owner would have a car that would cost him £10 to £50 a year less for its upkeep than an 80 x 150 mm., for the larger easy compression engine will go 10,000 and more miles without needing the pistons to be cleaned, and if the cylinders are separate, as they should be, then one’s own man can easily clean his engine without outside assistance. I can only repeat that the long stroke engine can be only a passing phase of engine design, and a very poor one and an expensive one for the every day user of motor cars. J.{Mr Johnson W.M.} KINGSTON BARTON. [18306.]—Mr. Pomeroy's article (page 1042) deals clearly and logically with a question that must interest all practical motorists. One is struck by the fact that his conclusions, drawn from accurate and extended testing, completely bear out impressions formed by ordinary use of various cars of different makes and sizes, and of recognised quality. In my own case, engines of 90 x 130 and 100 x 140 have proved extremely suitable under average conditions. A point that might be mentioned is that the larger the engine, the greater seems to be the necessity to keep the stroke-bore ratio moderate. The most regular and vibrationless engine of which I have had experience measured 75 x 120, a ratio that is, nevertheless, slightly in excess of 1 to 1.5; while, on the other hand, an engine of 100 x 160, precisely the same ratio, left something to be desired as regards vibration and power at reduced rates of revolution. Indeed in this latter respect it was markedly inferior to an engine of the same make measuring 100 x 140, notwithstanding its greater capacity. It is perhaps possible that there may be several points of view regarding the 80 x 120 engine, incidentally spoken of in Mr. Pomeroy’s article. Dealing with the origin of the 80 x 150, he mentions that its excessive length of stroke arose from the insufficiency of the 80 x 120; in other words, this engine might be of the desired type as regards stroke-bore ratio, but it was too small to be serviceable. Such an estimate is doubtless true, when applied to the cases of the many who wished to make these engines do the work of bigger ones, after the rating tax was imposed. For heavy closed bodies, or for touring with five passengers and luggage, such engines were certainly not ideal. To give them a chance the cars would have to be geared too low to be agreeable. Within reasonable limits, however, may we not admit that a well-designed engine, no matter what its capacity may be, will give satisfaction, if there exist a correct proportion between the power and the weight to be transported? Given this, the gear ratio may be arranged to let the engine do its work normally while the vehicle attains a sufficiently high speed. We have, in fact, a “lively” car. If too much is not expected of it, the engine of 80 x 120 may thus have a useful sphere and meet a certain demand. At the present time such engines are usually fitted in chassis of very moderate dimensions and sprung for light coachwork, and buyers may use them for two-seaters, in which case they make fast little cars of a very handy type; or with a slightly lower gear ratio, they seem well adapted to take a small coupé or a single landaulet for town use. With these uses in view, is it not possible that there may still be a market for the engine of 80 x 120 for work within its capacity? Autocar 23:11:12 S.D. | ||