Cecil Clutton Contemplates The "40/50" Napier
“An Important Landmark in English Automobile Design”
A Road Test in the Old Tradition
Motor Sport has always taken an interest in cars of mechanical beauty or interest, even though they are not sports cars. The “40/50” Napier merits attention by this criterion and it was, moreover, regarded as one of the high-performance luxury cars of its day.
The “40/50,” first produced towards the end of 1919, was an entire breakaway from the traditional Napier design of 1914 and earlier, which was an essentially Edwardian affair, with separate cylinders, copper water jackets and an unpleasantly forward radiator mounting. The.”40/50,” by contrast, was a very handsome machine, and the mechanical design represented all that Napiers had learnt about aero-engine design during the war which had just gone out of fashion, coupled with their previous experience of 6-cylinder motors.
It is interesting to see what Napiers themselves had to say about the engine in their lavish instruction book:
“The six cylinders (4 in. by 5 in.) are cast in one piece with their water jacket and the engine body, a special aluminium alloy being used. This construction gives great strength and stiffness, with low weight. Indeed, it is a fact that not only is this engine lighter than any prewar engine of equal power, but also its long life, its remarkable silence in working, and its freedom from vibration, are attributable to the rigidity obtained by this construction. A light steel liner is shrunk into each cylinder bore to resist wear.
“The valves are set vertically in the cylinder head. It has been proved that this position gives greater power, flexibility and fuel economy, than is obtainable with either ‘L’ or ‘T’ headed cylinders, while the new Napier swinging tappet system of valve actuation — which multiplies the motion of the cam and so allows the use of a small cam, with gentle slopes — leaves nothing to be desired in the way of silence.
“The pistons are of aluminium alloy. A special feature is that the expansion of the skirt is controlled by two steel rings so arranged that the piston expands, when heated, at exactly the same rate as the cylinder.
“The cylinder head is detachable for easy access to the valves, and for removal of carbon when necessary, although this engine very seldom requires decarbonising.”
It will thus be seen that the engine was a real pioneer of light-alloy construction, and it is a thing of beauty to behold. The whole of the outside of the engine is aluminium, very clean in design and almost of continental appearance. Induction is by a single S.U. carburetter (a very handsome affair with inclined dash-pot) on the off side, and dual ignition gets into the engine via sparking plugs screwed horizontally into each side of the head. The valves are vertically mounted, and slightly offset towards the inlet side of the block. They are driven by an overhead camshaft operating through rockers, the camshaft being placed between the fulcrum and the valve, in the manner indicated in the instruction book. The camshaft is driven from the front end by a vertical shaft and worm gears at top and bottom. Very narrow clearances were used — .002 in. and .003 in. when cold — and the valve diagram is highly peculiar, having negative overlap. The exhaust valve closes 2° after t.d.c., and the inlet valve does not start to open till some 3 1/2° later. In a high-speed engine such a late inlet opening would be very noisy, but this does not become apparent within the modest speed-range of the Napier engine, which is quite uncannily silent, and there is no trace of mechanical noise whatever from the engine.
The pressure-fed crankshaft is supported in a full complement of bearings and the rods are quite well proportioned, two-bolt, “H” section affairs, though in the earliest models they were tubular.
While everything in the basic design seems calculated to achieve lightness with efficiency, the actual power-output then seems to have been artificially restricted, as was so often the case with otherwise advanced designs in the early ‘twenties, so that one sometimes wonders why designers went to so much trouble when an ordinary side-valve engine would have given them their modest 18 b.h.p. per litre just as easily.
In the case of the Napier, it is quite clear that the engine could run quite comfortably up to 3,000 r.p.m., giving, perhaps, 120 b.h.p., but, in fact, it has not got a big enough hole to suck through, and dries up at about 2,000 r.p.m. Indeed, it has obviously said most of what it has to say at 1,500 r.p.m., but the effective peak was quoted at 2,000 r.p.m. with an output of 82 b.h.p., representing 13 b.h.p. per litre and 85 b.m.e.p. This was really quite logical, judged by the requirements of the time, when tyres were a limiting factor to speed (not to mention the 20 m.p.h. speed limit) and road-surfaces were mostly poor to middling. In a luxury car of this kind, predominantly intended for closed, chauffeur-driven coachwork, the normal running speed would not be generally in excess of 40 m.p.h., and it is in this range that the engine is so remarkably effective.
Incidentally, the epithet “40/50” almost instinctively brings to one’s mind about eight litres of engine, but the Napier engine is very much smaller than this, its six 102 by 127 cylinders giving a capacity of only 6 1/4 litres. Behind the engine comes one of the most perfect fabric-lined, single-plate clutches imaginable, and so on to a separate 4-speed gearbox of very compact and rigid design, the shafts running in roller bearings. Alternative back-axle ratios of 3.33 and 3.75 to 1 were offered, but the lower of the two was the normal, and with it the overall ratios were 3.75, 5.05, 6.75 and 13.3 to 1. The three upper ratios are therefore quite “sporting,” and with an engine encouraging greater use of the gears, it could be distinctly amusing to handle. But with the very flat-topped power curve of the Napier its potentialities are rather wasted, and a wide-spaced, 3-speed box would have served just as well. The spacing of the ratios, incidentally, is remarkably reminiscent of the “C”-type Bentley box. The gears are remarkably silent, and were probably almost soundless when new; they have the somewhat unusual characteristic that all three indirects produce exactly the same note. An unusual feature at that period is the centrally-mounted brake and gear levers — doubtless arranged so that the hired driver could nip smartly in and out to open and shut doors. The gear-shift is “back-to-front”; that is to say, one pushes the lever forward into the top speed.
The drive is taken aft from the gearbox through a massive torque-tube to the spiral bevel drive and fully floating back axle. The front end of the torque-tube incorporates an anti-rolling device, which operates by connecting links and trunnions on the front of the tube arranged so that when the tube tries to swivel, the twisting action compresses one or other of the springs and so resists the tendency to roll.
The chassis is fitted with semi-elliptic springs at the front end and long cantilevers behind. The wheelbase is 11 ft. 8 in. While the chassis looks relatively flimsy and unbraced by modern standards, it was considered outstandingly rigid in its day, and reaches its maximum depth at about the mid-way position.
The resulting chassis stiffness enabled the coachbuilder to fit a lighter body than was possible with the much more elastic chassis usual at that period, and this consideration for the coachbuilder shows how advanced was the general conception of the design. At a time when tyres were the limiting factor to speed and performance, the designer aimed to produce a car which, with its body, should be as light as possible, yet with a useful reserve of power. He achieved this by means of the light-alloy engine, and the relatively rigid chassis which, although itself heavier than need have been, repaid its weight by the lighter coachwork which it facilitated. The weight of the bare chassis was 25 cwt., and the overall weight with an open touring body was 37 1/4 cwt.
The chassis, in passing, was delivered in exchange for £1,750.
The original tyres were 895 by 135, but towards 1924, shortly before Napiers gave up motor-car manufacture in order to concentrate entirely upon aero-engines, low-pressure tyres were fitted, and a massive front-brake axle was also introduced.
Nowadays, “40/50” Napiers are rarely seen about, although the total number turned out between 1919 and 1924 was about 300. Fortunately, at least one of these fine cars is certain of proper preservation, since it is still in the hands of the Napier Company themselves. It came out of a long retirement to take part in the Jubilee Cavalcade in London, when it was operated by Guy Griffiths. The condition of the whole machine is remarkably good and the coachwork really sparkles. It is a thoroughly unostentatious body whose excellent proportions effectively mask the great size of the car. An excellent and unusual feature is the front pillars, which are exceptionally narrow and obstruct the driver’s vision hardly at all. The makers were the Maythorn Company.
Through the kindness of the Napier Company I recently had the privilege of taking this fine machine for a short run in the country, which, apart from the cavalcade, was the first considerable outing it had taken since before the war. From a driving point of view, one felt that one had in one’s hands a finely-designed piece of machinery, but that the enjoyment of the back-seat passengers, rather than the pleasure of the driver, had been the primary consideration. And, indeed, it would be remarkable if this were not the case. The steering is fairly heavy, though it was doubtless much lighter before the low-pressure tyres were fitted. This particular machine, made in 1922, was converted to the large tyres and front-wheel brakes in 1924. These tyres, in conjunction with a small steering wheel, calling for only 1 3/4 rotations from lock to lock, make it quite a muscular effort to circumnavigate a traffic roundabout.
As has already been stated, the clutch is a marvel. Light and sensitive in engagement, it is quite easy to get the heavy car, with a full complement of passengers, away from rest, on the highest ratio of 3.75 to 1, without the least judder or effort. However, the normal getting-away gear is second, bottom being an entirely emergency ratio. Upward changes are quite rapid for this type of engine, especially if the clutch-stop be employed. Downward changes require accurate assessment of engine speed if the wheels are to be meshed without commotion, and this is all the more difficult in view of the exceptional smoothness and silence of the engine at normal speeds.
The brakes are really effective, and must have been outstanding in their day. As against that, the immense weight of the front axle becomes very apparent when cornering at any speed, and one feels that it would not take much in the way of adverse conditions to get the car in a really ugly example of the dreaded sideslip. On slow, sharp corners it is certainly commendably free from roll, although if a roundabout is taken at any speed, some unusual noises suggest that the back end of the car is not notable for lateral location of the axle.
The gearbox need hardly ever be brought into play, as is shown by the useful top gear acceleration figure of 12 seconds from 10-30 m.p.h. Even this, however, is not quite as good as one would expect from an outfit giving certainly more than 3,000 litres per ton mile (assuming an overall weight for this car of 45 cwt., the figure is 3,100 on the 3.75-to-1 axle ratio).
As against that, the time for 0-50 m.p.h., using all the forward gears, is about 33 seconds, which is distinctly disappointing. It is, however, caused almost entirely by the very gradual acceleration after changing into top at 40 m.p.h., which is the useful maximum in third. Indeed, 50 m.p.h. is very near the useful maximum speed of the car, since the engine is reluctant to exceed 2,000 r.p.m., which represents 54 m.p.h. on the low axle, or 60 m.p.h. on the high, 3.33-to-1 axle.
The cruising speed is anywhere up to 50 m.p.h., when the engine is completely effortless and silent. Contemporary road-tests give a petrol consumption of 13-14 m.p.g. One of these tests was conducted in the Alps, including an ascent of the Stelvio. The whole trial, which was conducted by the R.A.C., extended over more than 2,000 miles, during which time the car gave no trouble at all, and neither oil nor water was added to the engine.
But the real qualities of the car become apparent in the back seats, which are really comfortable, although the springing itself is relatively hard (so much so, in fact, that the Autocar commented unfavourably upon it at the time). Yet even so, it affords a genuine comfort that is far more real than the swaying and wallowing which passes for comfort inmodern American productions. This stiffness of the springs also accounts in large measure for the freedom from fore-and-aft pitching.
The back-Seat passenger is at once soothed by the effortless travel, and impressed by the easy acceleration within the limited speed-range for which the car was evidently and purposely designed.
Back-seat driving is facilitated by a magnificent telephone (the chauffeur is, of course, carefully segregated in front of a glass screen) through which to scourge the driver with an unbroken flow of invective and advice. Most regrettably, it was not working when I took the car out.
Taking the car as a whole, one is strongly impressed by the advanced design, the handsome appearance of the engine, and the splendid workmanship. Its appeal to the non-driving owner is also . apparent, but it was a somewhat disappointing surprise to find that it was not more pleasurable from the point of view of the driver.
The “40/50” Napier is, nevertheless, an important landmark in English automobile design, and it is a cause for congratulation to the Napier Company that at least one example of their fine products will be safely preserved for posterity. [The “40/50” Napier wasn’t always such a sober performer as Maori suggests of the car he sampled. I recall photographing, with a No. 0 Brownie, an aluminium-bodied sports version when I was a youngster. And the car which Capt. A. G. Miller fitted with a cowled radiator and 2-seater racing body and ran at Brooklands in 1929 as the Auto-Speed-Special, did a standing lap at 68.79 and a flying lap at 78.18 m.p.h. The 1921 tourer which completed 2,000 miles under R.A.C. observation, covered the Brooklands half-mile at 72.38 m.p.h.—Ed.]