A New Mercedes-Benz.
A New Mercedes-Benz. Probably the most interesting exhibit, from the sporting point of view, at…
DSJ told me some time ago, I cannot remember in what context, that he could see I have no sense of balance. Which explains why I earn my living by moving words around, instead of as a high-wire walker or a trapeze artist. In internal-combustion terms balance is important and since reading the erudite and very enjoyable writings of Alex Harvey-Bailey, late of Rolls-Royce, as his father was before him, for the historical books of the Rolls-Royce Heritage Trust and the R-REC’s bi-monthly Bulletin, I have been encouraged to take a look at the problems of engine balance as they were encountered at Derby and Crewe.
As any student of automobile engineering must know, in a four-cylinder engine the primary unbalanced force is eliminated but the secondary unbalanced force remains, whose frequency is twice that of crankshaft rotation (the same applies to a 90 deg vee-twin engine), whereas a six-cylinder engine is in complete balance in respect of both primary and secondary inertia forces. This explains why those who pioneered in-line six-cylinder engines, like Napier, Sunbeam, Panhard-Levassor, Brooke, Spyker, etc, claimed great advantages in smoothness of running over cars with fewer cylinders. This would have been fine were it not that another factor affecting smooth running, that of torsional vibration induced by wind-up of the necessarily longer crankshaft, intruded.
ln the early days, before rubber and other forms of flexible engine mounts masked vibration in four-cylinder engines and crankshaft periods in six and eight-cylinder in-line engines, what would have been the near-perfection, a great superiority, of six-cylinder cars was marred by torsional shortcomings. S. F. Edge, the irrepressible advocate of the six-cylinder Napier, tried to kid his customers that any roughness felt was just the famous Napier “power-rattle”! Even Henry Royce (mechanic, not yet knighted) was in a bit of a pickle with his first in-line sixes.
Good balance the in-line six might have, but in those days the lack of torsional stiffness in its necessarily long crankshaft was accentuated because, to ease foundry problems, cylinders were often separate or in pairs, and bearings ill-fed of oil had to be extra-long, both factors which even further increased crankshaft length. Add to this the problems of properly carburetting six inlet valves from a single carburetter and it can be appreciated that the new-fangled six-cylinder cars of 1903 to 1906 had their difficulties.
At first the designers of such engines tended to use crank-throws angled at 180 deg, along the crankshaft, or sometimes at 60 deg, regarding the power unit as three two-cylinder units so coupled. The additional power impulses per revolution, compared to those of a four-cylinder engine, represented smoother torque but because the pistons of a six-cylinder engine followed an almost pure sine wave of some proportions three times per revolution, the flexible running and good low-speed pulling which Edge so loudly proclaimed, was allied to rough periods ending in a broken crankshaft if engine speed was allowed to reach a third of its natural frequence and the point of resonance. One remembers the broken big-end bolt that ended the great duel at Brooklands in 1908 between the six-cylinder Napier “Samson” and the four-cylinder Fiat “Mephistopheles”, the Fiat going on to win while the stricken Napier was driven slowly in. Vibration may well have caused the big-end failure, if the engine had been taken beyond the critical crankshaft speed.
When he became aware of these difficulties, Royce adopted the now usual arrangement of a six-cylinder engine arranged as two three-cylinder units front-to-back, with the crank throws at 120 deg. This is a partial solution to critical crankshaft vibration but not of torsional wind-up, which was aggravated in early engines by the habit, emanating perhaps from two and four-cylinder power units and poor carburation, of using heavy flywheels. This latter problem persisted into modern times and was very evident in the bigger six-cylinder engines (needing long crankshafts) made before the First World War. The 30 hp Rolls-Royce, which went into production in 1905, broke a number of cranks on test and when Daimler produced their first sixes around 1910 they proved unsaleable until Dr Frederick Lanchester had fitted them with his flywheel-type friction vibration dampers, which he had designed to overcome the same problem on the first six-cylinder Lanchester.
All the foregoing relates to the early days of engine development. What has been of interest and some surprise to me are the problems which Rolls-Royce still ran into between the wars, with what might be thought of by then as familiar areas of engine design. It has to be recognised, however, that due to the great interest that exists over anything “R-R”, and the Company’s careful documenting of engineering data, together with the recent writings of reliable historians like Alex Harvey-Bailey, much of what happened at Derby and Crewe is known about. Presumably other great manufacturers similar problems to contend with; until there is evidence to the contrary, we must assume this to have been so.
Nevertheless, I do find it somewhat surprising that Bentley and Rolls-Royce encountered so many problems at a comparatively late period in engine development, in the fields of engine balance, bearing materials, and the like. For instance, in one of his truly fascinating articles Mr Harvey-Bailey tells of how engine-bearing problems intruded after first 4 1/4-litre Bentleys had been introduced early in 1936. As the mileages on customers’ cars began to build up, so did main and big-end failures, although experimental work preparing E. R. Hall’s TT Bentley engine for the (cancelled) 1936 Le Mans race had suggested otherwise. The 3 1/2-litre Bentley engine had white metal bearings throughout, on a nitrided crank and running well within the capabilities of such bearings, it was immune from the problems now assailing those who drove fast and far in their 4 1/2-litre Bentleys. This was realised at Derby, and the R-R laboratory developed an aluminium / tin alloy for the bearings of the larger engine. These needed a larger running clearance than white metal. Partial grooving was also used to give a better oil-feed to numbers 1 and 5 big-ends.
Unfortunately, with the advent of more new Continental motorways, drivers were encouraged to cruise the new bigger Bentleys at 90 mph and higher and with the 4.0 to 1 axle ratio the bigger clearances with the new alloys allowed the crankshaft to run into the beginning of its crucial vibration period, which in turn hammered out the main bearings, and this starved the big-ends, causing these to fail as well. . . To effect a cure an increased capacity oil-pump and other lubrication improvements were introduced, and harder bearing alloy were used. Some big-end failures were, however, still experienced. A second hole drilled in the crank-pins was then tried. It seems, though, that complete reliability was not ensured until the harder bearing-alloys introduced to cure the original bearing troubles was abandoned in favour of the original alloy for the big-ends and a new alloy for numbers 1 to 6 mains, but going back to white metal for number 7 main bearing.
I had personal proof that there might be some doubt about the reliability of the 4 1/4-litre Bentley engine as late as 1938, and on Britain’s then-slow main roads at that, when I borrowed a Vanden Plus dh coupé to do a test for Motor Sport, suggesting a fast drive from London to John O’Groats. Bentley Motors was quite agreeable, but I was told that in the unlikely event of trouble intervening I was to book myself into a good hotel, try to get the car into a garage without broadcasting that it had broken down, and telephone Conduit Street. In the event, the car behaved impeccably, but was the possibility of bearing failure still in their minds? (What did fail were the India tyres which, in sound state at the start of the test, were down to the canvas 700 fast miles later.) Soon afterwards Rolls-Royce and Bentley announced that they were using Avon tyres exclusively. . . Incidentally, these Avons remain excellent tyres, whether you fit their motorcycle-size covers to your vintage Austin 7, or to a sidecar outfit come to that, or equip a fast car with the appropriate Avon-wear, as Rolls-Royce, Bentley, Aston Martin Lagonda and Bristol do today, and with take-overs in the offing, it is worth remembering that Avon is an all-British Company, employing local labour.
One assumes that with the advent of fast motor roads other designers had their problems and that Rolls-Royce’s difficulties have been highlighted only because of the availability of the data relating to these cars. Or were they exceptional, remembering that they related to an expensive 1936 engine running. up to not more than 4,500 rpm and developing at most 130 bhp? Perhaps engineers among our readership might care to comment?
In one of Mr Harvey-Bailey’s absorbing articles he mentions that in developing their cars overcoming their troubles “a large number of contemporary cars passed through the R-R Experimental Department over !he years, being thoroughly tested and examined in detail.” Well, one knows that makes such as Hispano-Suiza, Renault, Cadillac, Buick and Citroën have influenced Rolls-Royce specifications, such interchange of ideas being normal practice in the Motor Industry, as is the examination of many rival makes of cars. A 16-valve Bugatti was used by Royce, and when he was working on front-wheel-brakes for the Silver Ghost a Hispano-Suiza made fast runs between Derby and West Wittering. Another car R-R investigated at that time was an Isotta-Fraschini, and they also had an actual Le Mans Lorraine. In this context, an extremely interesting article written by James Fack and published in the Railton OC magazine, with permission from the Sir Henry Royce Foundation whose archives he consulted, brings fresh light to bear. It reveals that in October 1933 Rolls-Royce acquired for investigation an eight-cylinder Hudson-Essex Terraplane, and six months later got hold of a Terraplane Six. It seems that the Derby engineers were staggered by the smooth running and quietness of the eight-cylinder Terraplane, their Chief Engineer saying that the Hudson had the most outstanding engine of its kind he had ever experienced, previous straight-eights having lacked smoothness under acceleration. According to Fack, this was why the Phantom II’s replacement, the fabulous and extravagant Rolls-Royce Phantom III, had been laid out as a V12. At the time this was happening Daimler was dropping its “Double Six” range in favour of poppet-valved straight-eights! Fack claims that R-R saw the light later, which is why the Phantom IV was a straight-eight.
The Terraplane Eight was used by R-R to investigate their prevailing crankshaft torsional vibration bottlers. Removing the crankshaft damper from the American engine (when it remained free of any detectable vibration periods up to 4,300 rpm, when the valves bounced) and substituting a light-alloy belt pulley on the crankshaft, they found a sharp, slight half-period at 1,600 rpm. At 3,200 rpm in this condition there was a period in the Hudson engine of about the severity that a 20/25 hp Rolls-Royce engine developed at its half-period and there were very small-amplitude vibration periods at 2,000 rpm and 2,350 rpm. With the fan belt removed the inexpensive Hudson engine’s periods were increased.
Obviously intrigued, the R-R engineers fitted much stronger valve springs and then ran the splash-lubricated Hudson power unit up to 5,800 rpm still with the vibration damper removed. It remained remarkably smooth, slight clatter coming in at the equivalent of 70 mph in second gear. The simple Hudson engine seems to have made a quite devastating impact at Derby! Lord Hives wanted to put a Terraplane Eight engine into a 20/25 hp Rolls-Royce chassis to see if its refinement was due to its soft-rubber mounts. Meanwhile, having seen that a five-bearing eight was so satisfactory, the R-R engineers fumbled about, expressing such theories as that a seven-bearing six-cylinder engine with damper was worse than a four-bearing six without a damper and they wanted to put a nine-bearing eight motor, like a Nash or Chrysler, to the same test as that to which they had subjected the Essex Terraplane. Did other engineers work like this, I ask myself?
The Hudson Eight transplant was never needed, because the three-bearing, longstroke Terraplane Six caused all the consternation they could take! Rolls-Royce’s MD is reported as saying the Essex made his own Phantom II seem a noisy, rough car. He also regretted that it was definitely smoother and as quiet throughout its range as the 20/25 hp Rolls-Royce.
The R-R MD tried to console himself by saying there was a great deal in the American saying that a pound of rubber is worth a ton of theory . . . Nor was the Terraplane chassis much consolation for the R-R designers. They found that, while this chassis was very much stiffer in torsion than that of a 20/25 hp Rolls-Royce chassis, the bare Essex frame actually weighed 250 lb compared to 194 lb for the Bentley frame, yet it was a foot shorter in wheelbase and the overall weight of the American chassis was extremely low.
Lest it be thought that James Fack is biased against Rolls-Royce, I hasten to say that he admits that many aspects of the 1933 Terraplane, then selling at £330 in this country including 33.3% import duty, against £1,460 for the small Rolls-Royce, were pretty dreadful and indeed, that one R-R engineer remarked that it was astonishing that Hudson could actually sell 1,000 of the things a week! He also admits that R-R later introduced proper ifs, by 1935 (after looking closely at GM layouts) whereas Hudson didn’t until 1940. He concludes by suggesting that in the spring of 1934 Terraplanes could be considered better than they had any right to be, whereas the contemporary R-R products were not as good as they should have been. . . .
Reverting to the seemingly rather laboured solutions R-R applied to engine bearing failures, Mr Harvey-Bailey does quote the case of Lagonda, who adopted dural conrods running directly onto a hardened crank-pin for their V12 engine and as “when aluminium alloy seizes it does so quite savagely, as mileages built up they, too, had some nasty surprises”, at a time when Rolls-Royce and Bentley were producing “some broad smiles from the rest of the Industry” by their notices warning of the danger of driving their cars at continuous high speeds and recommending safe cruising speeds for the various models. Rolls-Royce rejected dural con-rods after an early development programme (but didn’t Alvis use such rods without a calamity, much earlier?).
It would be interesting to have the views of other ex-engineers of other Motor Companies on the foregoing. — WB
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