“Our good old engine with mechanically-operated poppet valves,” wrote Charles Faroux in La Vie Automobile in the spring of 1910,” is on its death bed. This is a fact which I pointed out to my readers some little time ago now; a fact which in the event seems to have been completely confirmed.” M. Faroux, whom all motoring writers must revere as their unquestioned doyen, and who has made so many sound prophesies in his time, will forgive me, I am sure, if I point out that on this occasion he was, for once, about as wide of the mark as he well could be: after more than forty years, “our good old engine with mechanically-operated poppet valves” is very much alive and kicking a good deal more vigorously than it was in 1910.
At that time, however, M. Faroux was by no means alone in his opinion. The trouble had all started with the appearance in Europe of an American, Mr. Charles Y. Knight, with an invention in which he had signally failed to interest motor manufacturers in the United States. From the first this invention had concerned an alternative method of gas admission and exhaustion which avoided the use of poppet valves, either mechanically-operated or otherwise, but the exact form which the invention took when Mr. Knight first arrived in Europe is not wholly clear from the record. In his first British patent, No. 14729 of 1905, the whole of the motor cylinder, which incidentally was air-cooled, was reciprocated in order to cover and uncover inlet and exhaust ports; but it seems that Mr. Knight fairly soon came to agree with later critics that this system was “crude,” and substituted for it the double sliding sleeve on which his fame has subsequently rested.
The patent covering this revised arrangement, No. 12355 of 1908, was not registered until June 6th of that year, but it seems clear that Mr. Knight had reached his solution of the problem considerably earlier and that by mid-1908 his invention had for some time been attracting rather intense interest among engineers in this country, many of whom had all along regarded the poppet valve, like the gearbox, as a nasty Continental makeshift. In particular, the Daimler company was at this period ripe for conversion to “some new thing.” In spite of all its tradition of seniority, and its Royal patronage, the Daimler company felt itself in danger of losing its premier position among British manufacturers. Upstarts like Napier had won the Gordon Bennett Trophy and then developed the six-cylinder engine; other upstarts like Rolls-Royce had won the Tourist Trophy and were beginning to claim pre-eminence for their six-cylinder model, chiefly on the score of its silence. Perhaps the Knight engine, which, according to its inventor, was inherently more silent than any poppet-valve design could ever be, would restore to Daimler its threatened prestige.
“For some time past,” announced the Autocar in September, 1908,” the Daimler company have been experimenting with a design of four-stroke motor in which the usual mushroom-type inlet and exhaust valves are entirely eliminated in favour of a pair of cylindrical sliding valves.” These experiments had evidently satisfied the Daimler engineers, and Daimler cars for the 1909 season, it was announced, would be fitted with the new design of engine. “The patent under which the 1909 Daimler is made,” continued the Autocar, “is that of Mr. Knight, who informs us that he is making arrangements whereby one manufacturer only in each country in which he holds his patent will be granted a licence to manufacture engines of his design.” Before very long the list of the chosen few was made known, and a pretty impressive list it was too: Daimler in England, Panhard et Levassor in France. Mercedes in Germany and Minerva in Belgium. Was it just chance, one wonders, or the effect of historical prestige on Mr. Knight’s American consciousness that led him to select, as the British, French and German recipients of his favours, the three original exploiters in their respective countries of the Daimler engine? No representative was named for Italy, although Italian cars in 1908 were at the summit of their prestige; but perhaps Italian engineers at that period were no more interested in silence than they have been at some subsequent epochs. In the United States, Mr. Knight chose as his protege the Pierce company, which at that time, apparently, was making a more expensive car than any offered anywhere else in the world; but in spite of his success in Europe, American engineers, it seems, were still nearly as reluctant to honour a prophet in his own country as they had been before Mr. Knight left home, and in 1910 the Pierce company was still hesitating.
The Minerva with Knight engine, “just like the Daimler’s,” was duly announced in May, 1909, but Panhard and Mercedes were much more cautious about taking the plunge. Indeed, in November, 1908, Messrs. Milnes-Daimler, Ltd., concessionaires in England for the Mercedes car, wrote to reprove the Autocar for being premature in its announcement on the subject. The Daimler Motoren Gesellschaft, manufacturers of Mercedes cars, they protested, have not arranged to manufacture the Knight engine. “The question of this engine is under consideration,” they added loftily, “and a trial will be made, but there is nothing decided as yet.” Panhard et Levassor, as far as I know, said nothing, but all their models for the 1910 season still had poppet-valve engines. In their case, as in that of Mercedes, the making of “a trial,” as mentioned by Milnes-Daimler, Ltd., was, one gathers, something of an understatement of what really happened. According to Mr. Knight, it was only, in both cases, after “terrific tests,” that they became convinced. However, in the end they were, and at the Paris Salon of 1910 both of them showed the Knight engine on their models for 1911. Even after this, as a matter of fact, Mercedes continued to sit on the fence, and persisted in making poppet-valve engines as well as those with sleeve-valves, which they fairly soon abandoned altogether. Panhard et Levassor, on the other hand, grew more enthusiastic as they went along, soon emulated Daimler in England by dispensing with poppet valves altogether, and continued, I suppose, to make the Knight engine after all other manufacturers had ceased to do so.
There can be little doubt that Mr. Knight’s somewhat invidious choice of what he regarded as the leading manufacturer in each country as the sole recipient of his favours caused considerable jealousy among others who by now were aspiring to the honour of pre-eminence. Moreover, remarks such as that of M. Faroux quoted at the beginning of this article only served to inflame their fears that they really were being left behind on a vital lap of the race. As only the favoured few could use Mr. Knight’s patent, there began a feverish search on the part of other manufacturers to find other alternatives to the supposedly moribund poppet valve. In England Napier registered a patent for the White double-sleeve valve engine, which presumably did not infringe Mr. Knight’s, Lanchester devised a single-sleeve-valve design, Rolls-Royce and Wolseley patented engines with piston valves. In France Renault designed an engine with a single sleeve to deal with the exhaust ports and an overhead inlet poppet valve, which must, one would have thought, have made the worst of both worlds: de Dion Bouton registered a design for a rotary-valve engine, but do not seem to have done anything more about it; while Darracq actually adopted and put into production the rotary-valve engine designed by C. E. Henriod — with disastrous results. Smaller manufacturers, and designers without any manufacturing facilities, let their imaginations run wild over a host of ingenious and generally unpractical solutions to the problem, culminating in the Broe engine shown at the Paris Salon of 1910, which had “rotating pistons with helicoidal grooves which put the combustion space into communication with the ports.” Even in Italy, Itala perfected a rotary-valve engine which, as a matter of fact, proved to be far the most successful of all the designs of this type and, indeed,may have come fairly close to causing a revolution in its favour.
While all this activity was going on on the drawing-boards, other, less inventive, manufacturers contented themselves with blandly declaring that the Knight engine and all other alternatives to the “good old engine with mechanically-operated poppet valves” were nothing but a snare and a delusion. And then, on October 15th, 1910, just when the excitement and controversy were at their height, the Autocar published an article entitled “Some Criticisms of the Slide-Valve Engine,” by “A Manufacturer of Poppet-Valve Engines.” The Editor, as he explained in a prefatory note, would have preferred to disclose the identity of the author, but this he was not permitted to do. On the other hand, he assured his readers that the criticisms had only been made “after actual tests of a 38-h.p. slide-valve engine.”
This last disclosure, of course, only made matters worse. Although the “slide-valve engine” criticised might have been made by Minerva, it was much more probable that it was a Daimler, and as the 38-h.p. was in fact the big model of the current Daimler range, this piece of information made it a virtual certainty that Daimler was the object of the criticism. In order to provide a modern parallel to the situation thus contrived, we must suppose, I suggest, that the Rover company had had its gas-turbine car in production and on the market for a couple of years, to the delight of a number of enthusiasts; and that at the end of this period a leading journal proceeded to publish “Some Criticisms of the Gas-Turbine Engine,” by an (anonymous) manufacturer of piston engines, after actual tests of a British car with a gas-turbine engine. The article, in any case, was assured of attentive readers.
The anonymous author divided his criticism into a number of headings, of which the first was Power. It was, he said, “very doubtful whether great horse-power for size, and especially for the weight of the engine, can be obtained with the slide-valve engine.” Its protagonists, although our critic did not specifically say so, pointed in this connection to the large size of the ports in a slide-valve engine; but, he contended, “excessively large ports are not needed on an engine until a high speed is reached,” and the makers of slide-valve engines “seem very chary of running these at high speed or with a high compression.” In other words it seemed “very doubtful” whether a high specific output could be obtained from a sleeve-valve engine, because no one had tried; and as the author did not claim that he had tried in the course of his “actual tests” with the 38-hp. engine and broken it in consequence, the criticism under this heading does not seem to get one very far.
The next heading was Silence, and indeed it would not have been surprising if it had been placed first in any criticism of the “Silent Knight” engine, especially as the author prefaced his remarks with the aphorism that “silence is golden” — which he applied, presumably, to engines rather than the manufacturers of the poppet-valve variety. At any rate, after admitting that “it might be thought that the slide-valve would be more silent in operation,” he went on to point out that in “an engine having the large and rapidly-opened exhaust ports which are a peculiarity of the sleeve-valve engine . . . the exhaust would be exceptionally noisy”; and without stating whether his “actual tests” had proved that this was so, suggested that “a manufacturer might think it necessary to fit exhaust pipes and silencer which would reduce the horse-power of the engine by 20 per cent. at 1,000 revolutions a minute and by 30 per cent. at 1,500 revolutions a minute.” “I believe,” he wrote, by way of summing up,” that no sleeve-valve engine has yet been built which is as silent (under load or running light) as the best six-cylinder poppet-valve engine.” This was a conclusion to which he might well have come as a result of the “actual tests”; but as these were carried out on a four-cylinder engine, he could hardly claim that he was comparing like with like, and he was constrained to add that “there is good reason to doubt whether it is possible to build a satisfactory six-cylinder engine on the sleeve-valve system,” which, of course, he could not possibly have proved by “actual tests” — unless he had tried to build one.
The next heading was Fool Proofedness, and although the parsing of the second word presents a bit of a puzzle it is soon clear what our author was getting at. “Another essential of a motor for pleasure cars,” he wrote, ” . . . is that it should be so constructed as to put it out of the power (as far as possible) of men who have little or no mechanical perception to injure or destroy it.”Chauffeurs, whom he describes as “cheerful gentlemen in leggings,” he continued, like racing engines light. “Now in the case of engines fitted with poppet valves, if an engine be thus improperly accelerated, the rollers actuating the valves are thrown off the face of the cams and a rattling is set up which warns the boldest chauffeur to desist.” In the slide-valve engine no such warning is given, and the only safeguard to which its maker can resort is to fit a carburetter so restricted that there is a loss of power of 20 per cent. at 1,000 revolutions a minute and of 30 per cent. at 1,500 revolutions a minute. Unfortunately he does not make it clear whether these losses and those arising from the silencing arrangements are to be regarded as cumulative; if the “actual tests” had shown that at 1,500 r.p.m. the 38-h.p. had lost 60 per cent. of its output, and only had about 15 h.p. at the flywheel, it must have begun to be a wonder that it could drag a big car along at all.
Under the heading Fuel Efficiency, he made no reference at all to his “actual tests” but contented himself with stating that it had yet to be shown that any sleeve-valve engine could equal the performance of the four-cylinder Vauxhall or the six-cylinder Rolls-Royce in the 2,000 Miles Trial of 1908. With regard to Engine Vibration, he pointed out that this was worse in four-cylinder than in six-cylinder engines, which would appear to be an irrelevancy, until one remembers his, actually quite unwarranted, assumption that it was impossible to build a satisfactory six-cylinder sleeve-valve engine; and then went on to say that in any engine, and whatever the number of cylinders, the valves must always be out of balance, which is more serious if they are of the sleeve variety, because they are then heavier. Which is at least a good theoretical point.
“So long as motor cars are driven by careless persons,” he continued under the heading Simplicity, “so long must it be necessary to eliminate as far as possible the necessity for constant attention by human beings to the working of the motor . . .” Sleeve valves, on this account, he claimed, are inferior to poppet valves because they need lubrication. “I am sure,” he added, ” that no manufacturer building internal combustion engines would think seriously of building engines of large size with the sleeve system”; from which, presumably, one can only conclude that the carelessness of drivers may be expected to vary with engine size.
“The owner of a luxury car,” he stated under the heading Smokelessness, “demands that his car shall be so constructed that he may drive in Hyde Park without fear of being expelled by a park-keeper on account of a smoking exhaust,” and he added that sleeve-valve engines are essentially smoky. One feels that he had something there, and one wonders whether the 38-h.p. had in fact been turned out of the park during the course of the “actual tests.” Under the heading Durability, however, he made no reference to these, merely stating that it had been proved for the poppet valve but not for the sleeve-valve engine, of which “many may be found on the roads of this kingdom giving forth a distinct knock,” a comment which, one would have thought, might have been applied to a good many poppet-valve engines also. Finally, he stated that as practically all Records are held by poppet-valve engines “the public would be foolish to be misled by statements to the effect that the poppet-valve engine is old-fashioned and out of date”; and concluded that the sleeve-valve engine is good on the bench, if silence, fool-proofedness, smokelessness, etc., are ignored. When modified for practical use, however, it has no advantage over the poppet valve.”
The Autocar had undertaken that the protagonists of the sleeve-valve would be given an opportunity to reply to this criticism, and in due course the reply came. As far as we are concerned, however, this aspect of the affair must be relegated to the sequel. In the meantime all concerned in 1910 were left in ignorance of the identity of the critic. My readers, more fortunate in this respect, can satisfy their curiosity at any time by referring to the files of the Autocar, just as one can establish “who done it” by cribbing the end of a thriller. I can assure them, however, that if they will but possess their souls in patience, all will be revealed in due course.