Some facts about an almost forgotten marque, compiled by Peter Clark from information supplied by Sydney Neal, who used to be with the English concessionaires and is now the Aerolite Piston maestro.
SO many present-day enthusiasts say sweepingly: “the old 3-litre Bentley, oh yes, a crib of the D.F.P.” and so few of them even know what the letters stand for that a little excursion into the hard realm of fact seemed indicated. It can be stated straight away that whatever coincidental similarities there may have been between other parts of the two marques, their engines had virtual nothing in common; with the exception of a none-too-successful push-rod o.h.v. design (or rather re-hash) which appeared after the Bentley was on the road, the D.F.P. engine was always a side-valve, whereas, as everyone knows, the Bently was single o.h. camshaft.
Bentley & Bentley, Ltd., of Hanover Street, W.1, were British Empire concessionaires for the D.F.P. prior to, and immediately after, the last war, and “young W.O.” used to provide propaganda dope for their very handsome catalogue by successfully driving special versions of the cars in many events. Early in 1914, for example, he captured a number of Class B records with a 2-litre unsupercharged car, at speeds up to 89.7 m.p.h. This car, incidentally, was really well streamlined in what has now been proved to be the best manner, bull-nosed in front and with a long tail. There are some splendid photos of it in the 1914 catalogue, but we cannot get hold of either the printing blocks or the originals, and it is impossible to re-photograph a fine screen half-tone reproduction with any success.
Production cars at this time offered to the English public were the “10/12,” the “12/15” and the “16/22.” The first-named was four cylinders en bloc, 65x 120 mm., with engine and gearbox in unit form. In spite of the latter feature, the clutch could be dismantled without unbolting the gearbox, which, so far as I know, cannot be done with any modern unit-construction assembly.
The “12/15” was, of course, the touring version of the 2-litre track car, and its four cylinders were 70 x130 mm. It had independent bottom caps to the main bearings, which enabled the bottom half of the crankcase to be dropped without disturbing the crankshaft. This was quite an uncommon feature in those days, when very often the top halves of the main bearings were in the top half of the crankcase, and the bottom halves in the lower part or sump, which, in addition to the usual bolts around the periphery, had long locating studs coming right up through to cylinder block level. This arrangement was used, for example, on the 1914 G.P. Mercedes, it much more advanced engine design in other ways. The gearbox of the “12/15” was not in unit with the engine. This model had a torque tube, but the smaller one did not. A “12/15″ Speed Model was also offered (on the strength of racing successes, no doubt) with larger valves, different timing, improved manifolding in and out, and a higher axle ratio. The model was distinguishable externally by a pointed radiator instead of a flat one, wire instead of artillery wheels, and larger tyres. The illustration, incidentally, shows none of these things! Special mention is made of the use of ”padded” gudgeons, a copper “pastille” being used in place of the apparently troublesome and fugitive grub screws. Nowadays, having described the Circlip in far more forcible terms, one resorts to a precisely similar aluminium pad.
The “16/22” had four cylinders 80 x150, cast in pairs, and the carburetter, like the Polyrhoe on the 1908 T.T. Hutton, reposed on the “wrong” side of the engine, with copper plumbing running between the two blocks and then dividing. One has the impression that, for reasons unknown, less effort was made to sell this model than the others.
All models had semi-elliptic springs fore and aft, worm and complete worm-wheel-steering, thermo-syphon cooling, Eismann magneto ignition with no advance and retard control, main bearings pressure lubricated, big ends splashed, gravity fuel tank leading to the much ballyhooed Claudel “Z” carburetter, and leather-lined internal cone clutch. Prices were (1914): £235, £290, £320 (Speed) and £340.
So much for the “book of the words” in 1914. Glancing behind the scenes, and also looking back to 1908-9 when the first models were imported, we find that a start was made with the “10/12” model, and that the engines up to 1911 were made by Chapuis et Dornier. At this point D.F.P. began to make their own engines, and for the next two years it is only mildly libellous to say that every chassis had a different engine; some C. & D., some D.F.P.; some 65 x120, some 85 x120, some 70 x120. There were also many changes in gear-ratio, and one can imagine the concessionaires having a rare old time trying to supply correct spare parts.
Late in 1912 came the “Type A” 2-litre job, known at first as the “12/15.” It proved to be their most popular effort, and with it came a measure of standardisation. However, gear ratios were changed three times in the next twelve months, and the tooth pitches, shafts and bearings inside the box were different each time.
The “16/22” first appeared in 1912 with chain-driven camshaft, which was followed by a quick succession or different gear-driven designs.
In 1913 the “10/12” was re-designed with a D.F.P. engine, and the “12/15” had a final burst of enthusiasm in the gearbox, acquiring stub teeth and splined shafts. The “16/22” remained virtually unchanged. The “12/15” Speed Model became known as the “12/40” and had aluminium pistons and lightened rods.
In 1920 we find Bentley & Bentley, Ltd., selling only that “12/40” model, virtually unaltered but for cantilever rear suspension. The chassis price rose (from £320 in 1914) to £675, to £750, and in June, 1920, to £850. By now the Bentley car was on the tapis, and the agency was taken over by B. S. Marshall, and the D.F.P. began to fade away.
The “10/12” re-appeared, not greatly altered, and late in 1922 came the pushrod o.h.v. “13/50.” This had unit-construction and a most troublesome single-plate clutch; it underwent many variations of connecting rods, timing and dynamo drive, axle shafts and other details, but appears to have finally “put the lid on it.”
It remains only to mention the “Petite” 9.5 h.p. 62 x 91 push-rod o.h.v. job, which is chiefly of interest as being the engine fitted to a few British G.N. cars, around 1923-1924.
Having now described the D.F.P. range of cars as they really were, I will make the suggestion that if the Bentley resembles them in any way it is because “W.O.,” in drawing up an exhaust manifold, a steering drop-arm, a fore-and-aft rod or other such minor part, made it from sheer force of habit like the D.F.P. he was so used to handling and working on. There are certain resemblances of this sort, the cone clutch and (externally) the “12/15” gearbox in particular, although which, if any, of the 101 different versions of the latter was copied it would be more than difficult to say! The rigid aluminium bulkhead behind the engine is also “very Bentley,” and the method of externally riveting the supporting brackets to the radiator shell.
The “12/15” and later “12/40” D.F.P.s were undoubtedly splendid cars in many ways. The 1914 Brooklands job would, but for the narrow section tyres and very youthful appearance of “W.O.,” be indistinguishable from many of the outer circuit cars to-day, especially in rear and three-quarter rear view. Their 1914 T.T. car did well to finish sixth, a lone entry against a very hot field, and was in appearance a well-advanced specimen of the road racing cars of the day.
My informant ran a “12/40” D.F.P. until quite recent years (I believe until he bought his present “12/50” Alvis), and it is interesting to think that the Light Production Company, one of to-day’s biggest piston manufacturers, grew out of designing the “Ward-Aerolite” piston to overcome the deficiencies of those early French aluminium pistons fitted to the D.F.P. “12/40.”