TO MEET THE TWINS
The Editor Invites YouTO MEET THE TWINS
LONG, long ago, when an economy car was a sort of fourwheeled motor-bicycle, the twin-cylinder engine was accepted as a perfectly normal form of power unit. Cyclecar constructors could not afford to be over-particular and usually had to get their engines from proprietary engine manufacturers whose most suitable unit was a vec-twin, which had evolved because it fitted conveniently into the frame of a motorcycle, that was shaped like that of a safety bicycle. If the cycle= maker wanted to use a simple transmission involving chains andior belts, he would set up his vee-twin in-line with the chassis frame and suffer from overheating of the rearmost Cylinder. If he was More ambitious he would place his power unit across the chassis So that when the vehicle was moving Cool air eddying round the barrels and heads, which could poke conveniently out of the bonnet sides, would provide some benefit in dispelling surplus heat.
In 1916. of 32 small Cars costing kuio or leas that were still available on the British market, 19 had a-cylinder engines, nine of which were air-cooled.
After the Armistice air-cooling achieved a new uplift, on account of the knowledge gained in building aero engines of advanced horsepower so cooled during the war. Post-war small cars like the flat-twin A.B.Q. and Rover Eight and 90° vce-twin Stoneleigh sponsored by Armstrong Siddeley were prominent vehicles that endorsed this new wave of enthusiasm for natural cooling, which was perhaps at its highest ebb in costing departments, where the price of radiators and their ancillaries were fully appreciated. On the other hand, if the twin called for fewer parts than a "four" and had a simple crankshaft, cost was increased by the need for roller bearings for the big-ends, etc. Strikes in the iron-founders industry probably contributed to the cult of the simple power unit, because a water-cooled 4-cylinder called for a comparatively complex casting and subsequent drilling and boring, whereas it was far easier to machine fins on a couple of aircooled cylinder barrels.
The drawbacks to air-cooling were overheating and noise. By 1919 it was realised that if the valves were placed overhead it was easier to avoid incandescence of the exhaust valve and distortion of the surrounding areas of the cylinder head, and Granville Bradshaw and Hotchkiss put both inlet and exhaust valves " upstairs," respectively in the A.B.C. and Stoneleigh. The Singer design that Rover adopted for their 8-lip. flat-rwin, and others, retained side-by-side valves however, sc . that, especially as the cylinders were less easy to expose than those of a veetvein, it was no unusual thing for the heads of this engine to glow cherry-red when climbing hills or idling in what traffic congestion London knew those days, and from the Rover's increase in holding-down studs from three to five one can deduce severe distortion of these inadequately Cooled heads.
Godfrey and Nash, when they realised that a 90° twin was preferable to one of 6o and that a heavy flywheel was needed for cyclecar work, designed their own engine for the G.N. This had the inlet valves overhead and the exhaust valves at the side; but for racing both valves were soon placed in the head.
These twin problems of heat and sound could be overcome by enclosing the cylinders in water jackets, as Jowett had demonstrated successfully on a flat-twin engine since 591o, but in the early 'twenties air-cooling had many devotees. !lumber, when they introduced the vcc-twin Humberette, had offered their engine in both airand water-cooled versions. But it' a simple twin-cylinder engine had been decided upon it was logical to cool it in the simplest possible way, relying on a good Oil to help out. The pros and cons of both methods were freely discussed and Granville Bradshaw threw in oil-cooling for good measure, but as early as 1959 two well-known motoring journalists, Wilfred Gordon Aston and B. H. Davies, were keen advocates of air-cooling. Mr. Davies, writing in The ,4mocar of the C.A.R. which had a radial 3-cylinder air-cooled power unit, said that on theday when President Poincare visited London it took hint half-an-hour to traverse Piccadilly from end to end but the engine showed no signs of overheating; he rather Spoilt this testimony by adding that " the motorist who lives in India or who wishes to climb Tornapress on a grilling day will rightly demand sterner tests." However, this allowed Mr. Aston to leap in with a letter of a length never permitted today in weekly motor papers, in which he expounded the splendid theory that at Mr. Davies Observed practically every water-cooled engine in
the Piccadilly traffic block he quoted generating steam, while he sat calmly in his C.A.R. car, the case for air-cooling was proved since, the temperature on the day of the President's visit being 45' F.., water-cooled engines had a margin of 167-1:., which was clearly insufficient—What, asked Mr. Aston, would happen to them. " in a country so hdt that the aunospheric temperature was 21214. ?" To drive his point home he also reminded readers that at to,boo ft. the boiling point of water is 93
The manufacturers did not all fall for these persuasive arguments but if not every small car Was water cooled, a great many of them had but two cylinders. liven Wolseley, who before the war had made the 4-cylinder Stellite light car, brought out a 7-h.p. horizontally-opposed twin even after their o.h.c. 4-cylinder Ten had left the drawing board—and while the twin was a niee little car, the Ten, for all its complexity derived from Hispano Suiza aero-engine practice, was abysmally slow, except when converted for racing by Alastair Miller.
The popularity of the twins was easy to explain. In those days small-6r owners invariably did their own servicing and repairs. To the low cost of manufacture the twin added inexpensive maintenance—four valves to grind-in or replace against eight, two sets of piston rings instead of four, only two plugs, four valve springs and guides, etc. Moreover, a head or barrel could he quickly removed or the entire engine carried into the kitchen, but when a four mis-fired the head gasket had to be disturbed and it was less easy to dismount a water-cooled block and cart it indoors. So the twin outlived the cyclecar. The excellent balance of the flat-twin came to be appreciated, even it' it was not so easy to c.arburate (using a single carburetter) as a vee-twin. Eventually, however, the Austin Seven killed-off -cyclecars and twin-cylinder small cars alike, except for jowett, who made a success of their " little engine with the big pull " up to the •outbreak of another World War.
The twin had its place in history and it is interesting (but not astonishing if you read on) to find that it has returned, if not to popularity, at least to gain a firm foothold in the field of modern design. This is proved by the table on the next page of twincylinder cars available on the British Market today. Compared to 4-cylinder power units these twins have no need to hide their hot heads in shame, remembering that the 848-cc. B.M.C. Minis Only give 37 maximum b.h.p. at 5,500 r.p,m., which is practically equalled by the N.S.U.. vertical twins of under 60o c.c. and the B.M.W. flat-twin of under 700 e.e. (and beaten by
b.h.p. in the case of the sports B.M.W. 700 twin); that Renault's 747 c.c.." four " developing 261 b.h.p. at 4,500 r.p.m. gives away quite a few horses to the D.A.F. twin of virtually identical capacity.
and that the Panhard Tigre, although giving away 146 C.C. to the Cooper-Minis, produces an extra five horse-power, or, conversely, in " cooking form," forfeits this amount Of power to the sporting members of the Mini tribe. The twins having fully justified themselves on maximum power, how do they fare in respect of torque ? Using the same comparisons we have Prinz 4— 32.5 at 3,250 r.p.M.) B.M.C.. Mini
B.M.W. 700— 44 lb./ft. at 2,900 r.p.m. 37 lb.M. at 3,400 r.p.m. D.A.P. 750— Renault 1(4
4z.95 lb/fiat 2.500r.p.m. 40.5 lb./ft. at 2.000 r.p.m. Panhard PL-r 7— Cooper-Mini
50.6 lb./ft. at 2,500 r.p.m. 54.5 lb./ft. at 3,60o r.p.m.
In the matter of torque then, the small " fours " score., but not sufficiently to turn a designer against twins, especially as there are motorists who actually prefer the punch of a twin to the smoothness of a " four."
The air-cooled twin will generally produce more noise than a water-cooled " four " but this is of far less moment in 1962 than it was in 1922, when only a thin piece of plywood isolated the driver from the power plant. Sound-proofing techniques of today mask much of the twins' cacophony, apart from which in many cases they have been banished to the back Of the vehicle and, in the case of the Fiat Giardiniera, laid to rest on their side beneath the floor. Rubber engine mountings of ti kind unknown in the early 'twenties help to smooth out any irregularities of balance and torque that temperamental twins may try to evoke.
Cooling problems have vanished, even with the engine at the back, now that fan-cooling is practical (which it certainly wasn't with meagre power outputs and restricted manufacturing facilities of the early post-Armistice period) but the many pronounced advantages of air-cooling remain.
The flat-twin is easy to endow with push-rod-operated inclined o.h. valves, which call for an overhead-Camshaft or specialised push-rod and rocker layouts in in-line engines. Surprisingly, not every flat-twin designer takes advantage of this (D.A.F. for example), but N.S.U. contrive to actuate inclined valves in their vertical twin with an overhead camshaft driven by Silent -eccentric links that were formerly the prerogative of those costly cars the Big Six Bentley and Leyland Eight (not forgetting the twin-cans Maudslay). llaving defended the twins and shown why they have the will to live, let us consider the circumstances of their birth. Alec Issigonis, Engineering Director of B.M.C., has told us that before finalising his brilliant Minicar he tried various power units, including air-cooled twins, but discarded them as undesirable. It must, however, be remembered that the extremely good, welltried 4-cylinder A-series water-cooled engine was already in production and was therefore the obvious one to use after reducing its capacity from 948 to 848 c.c. Put, had ii not been for ssiganis' adventurous genius in combining the gearbox with the crankcase and setting the unit across the front of the hull, it seems highly likely that a new engine, quite possibly a fiat-twin, would have
beets essential before the Mini's notable Compactness could have been achieved.
I ant suggesting that the use of water-cooled 4-cylinder engines instead of twins in very small modern cars is attributable to an accident of birth rather than design choice. When Renault laid down the new R4 they had ready to hand a 747-Cc. water-cooled " four " that had powered teeming thousands of 4 c.v. cars, so it was natural to adapt it, with new sealed liquid cooling to cock a snoot at carefree air-cooling. Combining this little in-line engine with front-drive has left no space to spare, and I recall examining an R4 in which the steering column made dip-stick removal all but impossible.
In the case of .Fiat it cats be assumed that its designing the 6m Dr. Dante (Iiacosa was influenced by the large number of even-smaller-capacity in-line H20,-washed " fours " the great Italian manufacturer for whom he worked had built since the inception of the original 570-cc. " 'Popolino." Certainly, after venturing a naturally-cooled twin for the Fiat 500 he declared himself so pleased with air-cooling that he wished he had made the Fiat &DO that way.
In all cases where there has been no convenient small "four " to hand, minicar designers have given birth to twins. B.M.W. had long experience of very beautifully made and finished flat-twins hit their shah-drive motorcycles, so naturally they used such ft power unit for their front-drive B.M.W. 700 small Car. N.S.U., too, drawing on motorcycle experience, and perhaps taking a glance at Fiat's little vertical-twin, installed an -o.h.c. engine of this type in the back of the Prinz. Incidentally, the N.S.U. vertical-twin is found in a number of variants, such as the Neckar. Goggornobil commenced with really small, simple cars, so Used vertical-twin 2-strokes (shades of the ktoo Carden) but decided on a flat-twin 4-stroke for their T700.
M. Boulanger, in planning the original 375-c.c. a c.v, Citroen, afterwards enlarged to 425 c.c., had clean paper on his drawingboard, Citroen's former 5 C.V. 850-C.C. 4-cylinder small car having been discarded many years earlier. D.A.F. could hardly put a lorry engine into a belt-driye morons.' machine. Both, therefore, used air-cooled flat-twins. Front the basic Citroen engine came the Ami 6, the Panhard 848-c.c. flat-twin, and the racing all. versions, of which the twin-plug 950-c.c. developed 69 b.h.p. Modern designers quite rightly tend more and more to place engine and driven wheels together and to do this its the mini-car field they are virtually forced to employ 2-cylinders-, whether or not they believe in them. They are, after all, merely following the precept of designers of rather larger small ears—flat-four in rear-engined VW and Porsche, vec-four at the back of the rearengined Zaporogets, flat-six its the boot of the Corvair, fiat-four under the bonnet of the f.w.d. Lancia Flavia, V4 for the coming Ford Cardinal. Although no present-day designer uses the air-cooled radial layout, as C.A.R. and Latitte did in 3-cylinder form and Fiffield-Allday with 5-cylinders in vintage times, D. K .W .—Au to Union achieve a short water-cooled cylinder block with their 3-cylinder 2-stroke engines. look again at the table-above and you will see that all the twins therein are either very compact little parcels or that in the case of Citroen. Panhard, and to Continued on page 272 MEET THE TWINScontinteed from page 266
a lesser extent D.A.F., they provide an exceptional amount of passenger/luggage space, so that a compact engine was called for.
Issigonis alone of modern engineers has found the solution to having the best of both worlds—saving his Corporation money by using an existing 4-cylinder water-cooled engine in a very small yet internally very spacious car. I shall be extremely interested to know what form of power unit Rootes adopt for their forthcoming rear-engined small cars, parts of which are being made, I believe, by Coventry-Climax.
If, as I do, you like twins and appreciate the many benefits of air-cooling, you will be glad that other designers have had to reach back to the Cyclecar Age, dusting up 2-cylinder technique, and providing us, in A.D. 1962, with a choice of at least ten different cars with these engines on the British market alone—I have not even started to think about the Japanese designs! Will someone, I wonder, go further and offer a flat-twin of the once popular I, too-c.c. capacity ? I tee no reason why this should not give an unstressed 85 b.h.p. in sports form.—W. B.