Daimler Double-Six piston engine was a sleeve-valve V12 engine manufactured by The Daimler Company Limited of Coventry, England between 1926 and 1938 in four different sizes for their flagship cars.
Daimler required an advanced new model to compete with Rolls-Royce's New Phantom of 1925. Though Packard had introduced its Twin-Six many years earlier it was to be a decade or more before luxury manufacturers like Rolls-Royce, Hispano-Suiza, Lincoln, Voisin and Lagonda made their own (and Packard returned to it). In fact by the mid-1930s flexible engine mountings and improved carburation had made so many cylinders unnecessary. What did return them to a certain level of popularity was the push for higher performance requiring higher crankshaft speeds. Daimler introduced their first 26 hp straight-eight in mid-1934 and their last (poppet valve) V12s were built in 1937 or 1938.
From 1929 Daimler Double-Sixes were distinguishable from the six-cylinder cars by a nickel bar down the centre of the radiator. A similar distinguishing mark was placed on the later Jaguar-made versions.
Aside from Daimler only Voisin in France ever attempted production of a sleeve-valve V12 engine. Voisin's production—between 1929 and 1937—was "minimal and spasmodic
The same Daimler Double-Six name was used for the badge-engineered Daimler V12 engine used in the largest Daimlers between 1972 and 1997. Lofty England, a Daimler apprentice 1927–1932, joined Jaguar in 1946 and became its chief executive. He ensured the Double-Six name was used for the Jaguar V12 when installed in Daimler cars.
This engine was designed by consultant Chief Engineer L H Pomeroy (1883-1941) to achieve high power with quietness and, particularly, smoothness. Pomeroy made the engine by taking the cylinder blocks of two existing 25/85 hp Daimler engines and putting them on a common crankcase. Pomeroy was to be appointed managing director in 1929. The same design was produced in different sizes depending on the different engine displacements.
|Manufacturer||The Daimler Company Limited|
|Also called||Daimler Double-Six|
|Predecessor||57 hp inline six-cylinder|
|Configuration||60 degree V twelve-cylinder|
|Displacement||7.136 litres (435 cu in)|
|Cylinder bore||81.5 mm (3.2 in)|
|Piston stroke||114 mm (4.5 in)|
|Cylinder block alloy||Cast iron, cast in blocks of 3 cylinders Alloy pistons running in light steel sleeve-valves|
|Cylinder head alloy||Cast iron? detachable, separate head for each block|
|Valvetrain||Sleeve-valves, double light steel sleeves operated by pushrod from chain-driven eccentric shafts in the engine block|
|Fuel system||Twin 7-jet Daimler carburettors with pre-heated air supply, petrol supplied by mechanical pump mounted near the carburettor. Ignition by two magnetos and battery and coil|
|Oil system||Submerged pump, separate radiator|
|Cooling system||Water: belt-driven four-blade fan and radiator|
|Power output||150 bhp (110 kW; 150 PS) @ 2,480 rpm|
Announced 15 October 1926 and observed by The Observer's motoring correspondent to be Britain's first twelve-cylinder car engine.
Power output 150 bhp (110 kW; 150 PS) @ 2480 rpm. Tax rating 50 hp
The result was an engine which idled at 150 rpm and ran with uncanny silence "the only audible sound made by a Double-Six (if you opened the bonnet and went right up to it) was the almost imperceptible tick as the ignition points opened and the faint breathing of the carburettor".
This largest engine faded from the catalogue after 1930
Announced 1 August 1927. Formed around a pair of 16/55 cylinder blocks
Power output 100 bhp (75 kW; 100 PS), Tax rating 31.4 hp
Production ended in 1932, none with fluid flywheel and pre-selector gearbox.
Announced October 1930 and matched with the new Daimler fluid flywheel and Wilson pre-selective half-automatically changing four-speed gearbox.
Tax rating 40.18 hp
In November 1930 a car was shipped to Edsel Ford with the new Daimler transmission. It aroused so much interest Cadillac's chief engineer, Ernest Seaholm, came to the following Olympia show and bought another for technical investigation. It inspired Earl Thompson, who invented syncromesh, to develop the Hydramatic transmission.
This light double-six was one of the first cars designed using ergonomics. Switches buttons and stalks were all placed within finger tip reach of the driver and accessible without taking hands from the wheel. The cars would run up to 40,000 miles or 60,000 kilometres before requiring engine decarbonisation.
This model was usually supplied with a taller and more slender radiator.
Announced October 1930 and matched with the new Daimler Fluid Flywheel and Wilson pre-selective half-automatically changing four-speed gearbox.
Tax rating 49.4 hp
Cylinder block a one-piece light alloy casting
From 1935 to 1938 nine Double-Six 40/50 engines were made with poppet valves - possibly to use surplus components.
The Autocar reported in April 1927 the big cars needed no other gears once they were rolling, even climbing a hill. Petrol consumption was not so savage as might have been expected at 10 miles per gallon. "2 to 82 mph in top gear in the highest degree of smoothness and quietness" said The Autocar ". . . fortunate beings will leisurely survey the moving surface of the earth through the windows of their Daimler Double-Sixes as they pass onward in silent dignity".
Bodies were all mounted after the Daimler pattern on a separate frame flexibly held.
A contemporary press report remarked that "when the Double-Six arrives at the door there is no obvious pomp and circumstance. Here is a car that looks clean-cut and aristocratic in its speckless grey paintwork. It is not until one comes close to the car that its great size is realised". "The Daimler bonnet is nearly level with the chin of the observer." Autocar
William Boddy of Motorsport commented that the difficulty with sleeve valves was lubrication. So much oil near the combustion chambers led to a gummy engine prone to seize if left standing for any length of time. Attempts to tow-start invariably led to sleeve-driving link breakage if not damage to the sleeves. There was also difficulty in timing the sleeves once pistons had been out of the block and also synchronising carburation and ignition between the two banks of cylinders.
Daimler introduced their new Straight-Eight in 1934 and Double-Sixes slipped slowly from the catalogue.