THERE are no doubt many readers who, like myself, find a great dell of interest in studying unusual mechanisms of all kinds. This is as it should be because the underlying motive behind nearly all model engineering is a love of mechanism for its own sake, apart from what duty it performs, or its ultimate utility.

One of the reasons why we admire the engines of a past age is because, no matter how crude and inefficient they are according to modern standards, they evince ingenuity of conception and individuality of thought which as is only too rarely encountered in the present austerely utilitarian age.

In the field of internal combustion engines, one sees few attempts nowadays to break away from well established principles of design, and despite their diversity of form, engines for various purposes have much the same basic mechanical design. The efficiency expert will say that this is because salient features have been proved by experience to be the best for their practical purpose, and that there has been a weeding-out of principles and features which, however ingenious, have not stood the test in the hard school of everyday utility. While it is probable that this view would be generally endorsed by engineers, it is by no means a foregone conclusion which should be accepted without further examination. It is not unreasonable to believe that some of the ingenious forms of design which have been tried in the past--and at the time, been found wanting--might if properly developed, have been just as successful and efficient as those which have now become an integral part of orthodox or conventional practice.

Many examples could be cited where an old idea, which at the time of its inception was unsuccessful, generally because of limitations in metallurgy or methods of machining then available, has been revived and has proved to be the answer to a modern problem. Indeed, one may say that few of the mechanical ideas incorporated in the latest machines are themselves new in conception; more often they are, like most of the jokes of radio comedians, minor variations on very old themes. True ingenuity, based on sound principles of physical and mechanical science, is never ultimately wasted, and though the original author of a bright idea may never reap the reward of his ingenuity, it is fairly certain that someone eventually will.

From time to time, readers of the MODEL ENGINEER who unearth rare specimens of old mechanism ask me to identify them, or to advise them regarding their origin, purpose and history. These specimens range from complete machines to mere fragments-lam sometimes called upon to perform a feat of reconstruction equal to that of the palaeontologist who gives a detailed description of a dinosaur on the strength of evidence provided by a single bone-but in nearly all cases they exhibit the ingenuity of a dead and forgotten inventor. What matters is , that the ingenuity may have been misguided or misplaced? It is all of intense interest to the engineering enthusiast, and represents some phase of the eternal wrestle with mechanical problems which occurs all along the path of progress.

This preamble constitutes my excuse-if excuse be needed-for introducing to readers the description of an engine which is far removed from the type of thing usually in the minds of model Le. engine enthusiasts-and perhaps some of my readers will find it, for that very reason, a refreshing change. It will, at any rate, remind them that there are other possible types of engines than those which are predominant-often to the point of monotony-in the model engineering world today.

Some time ago, an engine of an unusual type was brought to my notice by Mr. Hammond, of Clerkenwel1, who had acquired the engine in the course of his business as a dealer in second-hand machinery, and had been trying, without success, to trace the maker or inventor.

In this latter respect, I have so far been unable to give him much assistance, but the description he gave of the engine aroused my curiosity, and after a preliminary inspection, it was loaned to me for a closer and more detailed examination.

Two-stroke or Four-stroke?

From a cursory inspection of the outside of the engine, one might easily jump to the conclusion that it was a two-stroke "valveless" engine of a very archaic type, as it has no exterior evidence of any valve mechanism, and the position of the exhaust and inlet ports on the cylinder barrel is more or less in keeping with this idea. Some of the early two-stroke engines, built for marine or stationary purposes, had a long stroke in relation to their bore, besides a much longer piston and connecting rod, and a smaller annular water jacket space, than is common in modern practice, producing the lean, spindly appearance characteristic of the" genuine antique" in engines of this class. But even after stripping the engine, and revealing its highly ingenious valve timing gear, one might still conclude that it was a two-stroke of an elaborate type, in which an attempt had been made to improve upon the port timing by the incorporation of mechanical timing gear.

It may be mentioned, for the benefit of the readers who have not studied the history and evolution of i.c. engine design, that there have been many such attempts, particularly in the early days of the two-stroke engine, when this particular type was a happy hunting-ground for many inventors. Almost every known type of valve and method of operation has been exploited in innumerable patents for improved two-stroke engines, few of which ever reached the production stage, and still less survived for any length of time.

The reason why these inventions "missed the boat" was that they sought to remedy the glaringly obvious limitations and faults of the simple engine, without taking into account g practical virtues of mechanical efficiency, freedom from trouble, and low initial cost, which are often more important from the utility point of view than obtaining the utmost economy or power output. Very often the gain in efficiecy produced by considerable elaboration is more theoretical than actual, being more than offset by mechanical losses in the valve operating mechanism. But perhaps I am guilty of digression, so we will leave this diverting subject and "return to our muttons," as they say in France.

The engine is, in actual fact, a four-stroke, the valve events being controlled by a rotary piston-cum-sleeve-valve, operated by means of a skew gear attached to the connecting-rod, and meshing with a "face worm" or scroll gear on the face of the crank disc, concentric with the crankpin. It may be mentioned in passing that this form of valve although unusual, is by no means unique in i.c. engine practice. About thirty years ago, considerable publicity was given to an American engine which had a rotating piston, so designed as a sleeve valve; but it proved to be a 'nine-days' wonder, and was never a commercial success. The use of a rotary sleeve valve surrounding a more normal type of piston, and operated by spur and worm gearing from the crankshaft, was somewhat more successful, and I remember working on an electric generating plant, also of American manufacture, and known as the "Silent Alamo," in which such an engine employed.

But the engine now under discussion almost certainly pre-dated these examples by many years I should estimate that it was the earliest engine having such a valve gear that I have ever encountered, either on paper or "in the flesh." Moreover, it lacks nothing in ingenuity; the type of gearing, and the use of a connecting-rod composed of two bars, one of which forms the shaft of the skew gear, being probably unique.

The piston is in the form of a long sleeve-actually twice the length of the stroke--with a partition in the centre, forming what would normally be the "crown." No piston rings are fitted, and it has two diametrically-opposed round ports above the partition, which each uncover inlet and exhaust ports in the cylinder wall, the speed of rotation of the piston being one-fourth that of the crankshaft. A rather elaborate form of universal joint, comprising a ball and socket in conjunction with a pin and die blocks, is used to transmit the rotary motion from the skew gear shaft to the piston.

It will be noted that the upper part of the piston forms combustion chamber, and in order to enable sufficient compression to be obtained, the detachable cylinder-head is made with a spigot or "junk head," 21 in. in length, which passes down inside the piston sleeve. A tapped hole is provided in the centre of the spigot, presumably to take a sparking plug, the body of which is sunk into the spigot, so that it does not need to have an abnormally long reach. No ignition equipment was fitted to the engine at the time it came to my notice, but there was a small sprocket on the shaft, behind the flywheel, which might have been fitted, either originally or subsequently, for driving a magneto.

The engine has a bore of 2-1/4 in. and a stroke of 3 in. Its overall height is 17-1/4 in., and the flywheel is 10 in. diameter by 1-1/2 in. face width. The body of the engine is a single casting, including the cylinder barrel and water-jacket, and a broad circular flange 10 in. diameter, on the underside, which forms the mounting pedestal. A rather unusual form of crankshaft construction is adopted, incorporating a main journal with a large cast-iron disc, apparently riveted on, forming both a balance weight and an internal flywheel. The crankpin, outer web and journal appear to be in one piece, riveted into the disc, and the scroll gear appears to be either cast or machined integrally with the disc. As the crankshaft assembly was badly bent, no attempt has been made to put the engine into working order so as to enable a running test to be carried out.

As the engine was intended to run on gas, no carburettor is fitted, but a somewhat elaborate (though not very scientific) gas mixing valve is provided in its place. This incorporates a screw-down valve which presumably controlled the admission of air, and a small mushroom valve, presumably for gas, with a long stem extending through a guide bush, and possibly intended to be controlled externally, either by hand or some form of governor, though there is no sign of the latter having been fitted.

A rather interesting feature about the gas mixing valve-and one that gives some clue to the period of the engine construction--is that no proper provision is made for its attachment to the cylinder wall, such as by a machined flange or facing. It has a curved saddle piece which was presumably filed as truly as possible, likewise the circular face of the cylinder wall to which it was bolted, though no very high degree of precision appears to have been achieved, and even with a thick packing gasket, it must have been difficult to avoid leakage at the joint. Such methods of attachment were not uncommon in early engineering practice, before the machining facilities of the modern engineering works were generally available. It can' hardly be that the need for an attachment at this point was overlooked in the design, in view of the care taken over other details; but one cannot imagine that any modern designer would have neglected to provide some macbinab1e facing for so important a component as a gas mixer or carburettor.

I have already given some reasons--or excuses, if you prefer--for bringing this engine to the notice of readers. One of my critics has recently accused me of going to too much pains to "justify my opinions," or my reasons for doing things, but I think that most of my readers share my passion for finding out the why and wherefore of everything, and are not contented with knowing bare superficial facts. It is this spirit of investigation which is responsible for all human progress, not only in engineering, but in all other fields of thought.

We were often told in our youth (by adults who didn't wish to go to the trouble of answering our innumerable questions) that" Curiosity killed the Cat "-but I feel sure that every one of its nine lives must have been well spent! (By the way, I have always wanted to know what cat?--and how was it killed, and why?--and more important still, what was it trying to find out?)

It is possible that other readers may have encountered the type of engine described, and may be able to give some further details, concerning its origin; if so, I should be glad to hear from them, and to pass on to readers any further information thus obtained. To those who are not so much interested in the historical side of research, there are still object lessons in this and many other ingenious types of old engines, which even the most ultra-modern engineers cannot afford to disregard. An engine of the type described, if redesigned and brought fully up to date in the light of modern experience, would certaiIlt7 work quite well, and might even prove to have practical advantages over the conventional form of design. It could be made lighter than an ordinary four-stroke engine, and with adequate porting, and precision fitting of the piston sleeve, could be made to produce a high cylinder efficiency with the minimum mechanical losses. The principle is also adaptable with equal facility to two-stroke engines, enabling more efficient port timing to be attained, with the ability tr delay the closure of the transfer port, a feature so desirable yet quite unattainable in the present form of two-stroke. The use of the piston as a valve has many mechanical advantages over any other form of valve gear, provided one can man it do exactly what is required. In sleeve valve design, it is generally accepted that the combination of rotary and reciprocating motion results in a reduction of friction as compared with straight-line motion, and this feature is found in most modern sleeve-valve engines.

Model engineers are notoriously assiduous in their search for the buried treasures of the junk yards. Let us not forget the possibility of the junk yards and lumber rooms of history from whose dusty recesses may often be gleaned a long-forgotten gem, all the more valuable faits antiquity and sentimental value; why, who knows?--it may even prove to be a genuine "old master," the value and interest of which has been enhanced a hundredfold by its long seclusion. Old text-books and catalogues, too, are prolific hunting-grounds for the mechanica. enthusiast, and will often yield rich--and rare specimens of the art and craft of a past engineering epoch.

I take this opportunity of thanking Mr Hammond for bringing this engine to my notice and giving me facilities for dismantling and examining it in detail. ETW ME vol 101 no 2519, Thurs Sep 1, 1949, p273.

Reference:

The Model Engineer, Percival Marshall & Co. Ltd. Volume 101, Number 2519, Thursday Sep 1, 1949, p273.