The Daimler Double-Six sleeve-valve V12 was a piston engine manufactured by The Daimler Company Limited of Coventry, England between 1926 and 1938. It was offered in four different sizes for their flagship cars.
The same Daimler Double-Six name was used for the badge-engineered Daimler V12 engine used in the largest Daimlers between 1972 and 1997.
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 carburetion 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 chromium 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."
Lofty England,[1] 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.[2]
This engine was designed by[3] 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.
| Daimler Double-Six (50) | |
| Manufacturer: | The Daimler Company Limited |
| Aka: | Daimler Double-Six |
| Production: | 1926-1930 |
| Predecessor: | 57 hp inline six-cylinder |
| Successor: | Double-Six 40/50 |
| Configuration: | 60 degree V twelve-cylinder |
| Displacement: | 7.136L |
| Bore: | 81.51NaN1 |
| Stroke: | 1141NaN1 |
| Block: | Cast iron, cast in blocks of 3 cylinders Alloy pistons running in light steel sleeve-valves |
| Head: | 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 |
| Fuelsystem: | 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 |
| Fueltype: | Petrol |
| Oilsystem: | Submerged pump, separate radiator |
| Coolingsystem: | Water: belt-driven four-blade fan and radiator |
| Power: | 150bhp @ 2,480 rpm |
Announced 15 October 1926 and observed by The Observer's motoring correspondent to be Britain's first twelve-cylinder car engine.
Bore and stroke 81.5 mm x 114 mm gave a swept volume of
7136 cc
Power output 150bhp @ 2480 rpm.
Tax rating 50 hp
6a 5a 4a 3a 2a 1a
1b 2b 3b 4b 5b 6b
order of firing: 1b 1a, 5b 5a, 3b 3a, 6b 6a, 2b 2a, 4b 4a
The exhaust pipes passed through the V of the cylinder blocks and were covered with an aluminium plate to dissipate heat.
The engine and clutch were mounted as a unit separately from the gearbox[4]
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
Type O wheelbase 155.50NaN0 Track 600NaN0
Type P wheelbase 1630NaN0 Track 600NaN0
Type W wheelbase 155.50NaN0 Track 570NaN0
7.30NaN0 x 370NaN0 or
6.750NaN0 x 330NaN0 or
6.750NaN0 x 350NaN0
Length 2230NaN0
Width 760NaN0
Height 820NaN0
Announced 1 August 1927. Formed around a pair of 16/55 cylinder blocks
Bore and stroke 65 mm x 94 mm gave a swept volume of
3744 cc
Power output 100bhp,
Tax rating 31.4 hp[5]
Petrol was lifted to a reservoir by the engine from the rear-mounted tank by Autovac[6]
Type Q wheelbase 1310NaN0 Track 520NaN0
Type M wheelbase 1410NaN0 Track 520NaN0
Type V wheelbase 1420NaN0 Track 540NaN0
Type O wheelbase 1450NaN0 Track 600NaN0
5.250NaN0 x 310NaN0 on the coupé tested by The Times[5]
Length 1900NaN0
Width 650NaN0
Height 720NaN0
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.
Bore and stroke 73 mm x 104 mm gave a swept volume of
5296 cc[7]
Tax rating 40.18 hp[8]
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 synchromesh, 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 40000miles before requiring engine decarbonisation.
Engine
Cylinder block a one-piece light alloy casting
Distributors were moved to the back of the engine
Cover plates provided in the crankcase which could be removed to reveal the sleeve-eccentric links
Carburettors moved forward
Lubrication by two submerged helical-gear pumps, one feeding all moving parts, the other circulating oil through the oil radiator
Oil radiator to maintain a constant 130°F
Cold viscid oil forced open valves allowing oil into troughs below the big-ends to provide cold-start splash lubrication of the sleeves
Hand-operated oil cleaner
Water pumps on outside of each cylinder bank mounted in tandem with dynamosThis model was usually supplied with a taller and more slender radiator.Chassis
Grouped chassis lubrication
Back axle incorporating dip-stick cum oiling syringe
Hydraulic shock absorbers
Short wheelbase 1380NaN0 Track 600NaN0
Medium wheelbase 147.50NaN0 Track 600NaN0
Long wheelbase 1570NaN0 Track 600NaN0
Announced October 1930 and matched with the new Daimler Fluid Flywheel and Wilson pre-selective half-automatically changing four-speed gearbox.
Bore and stroke 81.5 mm x 104 mm gave a swept volume of
6511 cc[7]
Tax rating 49.4 hp[8]
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".
A letter from Tony Bird in the January 1967 issue of Motor Sport recounted how Double-Six models could develop violent front axle "wheel wobble" which could only be overcome by stopping the car.
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[9]
William Boddy of Motor Sport 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.[10]
Daimler introduced their new Straight-Eight in 1934 and Double-Sixes slipped slowly from the catalogue.
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