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 (19 kW) straight-eight in mid-1934 and their last (poppet valve) V12s were built in 1937 or 1938.[1]
From 1929 Daimler Double-Sixes were distinguishable from the six-cylinder cars by a chromium bar down the centre of the radiator.[2] 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."[3]
Lofty England,[note 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.[4]
Design
This engine was designed by[5][note 2] 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.[1] The same design was produced in different sizes depending on the different engine displacements.
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
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 150 bhp (110 kW; 150 PS) @ 2480 rpm. Tax rating 50 hp
Cylinders arranged in blocks of three
Pistons were of light alloy and split-skirted "like the modern girl"
Double light steel sleeves controlled the inlet of fuel and the outlet of exhaust, they were operated by short connecting rods from their eccentric-shafts
Separately detachable cylinder heads
60 degree angle V
Crankcase aluminium
The big-ends lay in pairs, the right-hand ones forked so that diagonal pairs of cylinders were in the same plane
Connecting rods were H-section
Crankshaft ran in seven bearings and had an external Lanchester-type vibration damper at the front
Two sleeve-operating eccentric-shafts were driven by chain at the rear of the engine each ran in four bearings
Daimler seven-jet carburettor, water-pump, magneto, exhaust pipe and silencer were duplicated, each block of cylinders having its own components
Petrol was supplied to a reservoir by the engine from the rear-mounted tank by air pressure
Each Daimler carburettor had an independent pre-heated air supply and four jets plus a primer which acted as a pilot with a separate air supply
Inlet manifolds were water-heated and mounted on the outside of each cylinder block
With the primer lubricant was passed to the cylinders and with the depression of the starter pedal oil delivered to the lower end of the sleeves
Oil was forced to the main and big-end bearings, the sleeve-shafts and the sleeves
Oil was cooled through a radiator
35/120 "His 35/120 hp cars were nothing like worn out, so instead of ordering the new model the King had "Double-Six" engines installed in his existing Daimlers. However, by the end of 1927 His Majesty had taken delivery of a complete V12 model"[1]
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
Dual ignition was fitted
Distributors were coupled as were all the change-over switches from the coil to magneto ignition
Magnetos and water pumps were driven through transverse shafts by skew gearing from the nose of the crankshaft
Dynamo operated by silent chain
Two vertical shafts from the same source drove contact breakers and distributors set above the cylinder banks
Belt-driven four-bladed radiator fan
Fuel was pumped from the rear tank by air pressure from a mechanical pump mounted near the carburettor
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[6]
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".[7]
This largest engine faded from the catalogue after 1930[1]
Chassis
Chassis frame was channel section
Gearbox: driven through a single dry plate disc clutch mounted on the engine a separate four-speeds and reverse gearbox was mounted on a very substantial cross-member and controlled by a central ball-gate gear lever.
Hand brake operated shoes in a brake drum mounted at the back of the gearbox
Power was taken by open propeller-shaft with metal universal joints to a (virtually silent) underslung worm-drive to the rear axle
Suspension was by gaitered half-elliptic leaf springs - beneath the axle at the back
Brakes on four wheels were rod-operated with assistance from a Dewandre vacuum servo positioned beside the gearbox. Adjustment could be made by hand
Steering: the width of the engine necessitated mounting the worm and sector reduction box on the scuttle. From there a coupling lever dropped to a bell-crank pivoted on the chassis side-member. A normal drag-link ran to the front axle.
Wheelbase:
Type O wheelbase 155.5 in (3,950 mm) Track 60.0 in (1,524 mm)
Type P wheelbase 163.0 in (4,140 mm) Track 60.0 in (1,524 mm)
Type W wheelbase 155.5 in (3,950 mm) Track 57.0 in (1,448 mm)
Tyres:
7.3 in (185 mm) x 37 in (940 mm) or
6.75 in (171 mm) x 33 in (838 mm) or
6.75 in (171 mm) x 35 in (889 mm)
Dimensions of standard saloon de luxe:
Length 223 in (5,664 mm)
Width 76 in (1,930 mm)
Height 82 in (2,083 mm)
Prices
Chassis prices: Type O £1,850, Type P £1,950, Type W £1,950
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.[12]
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 removing their hands from the steering wheel. The cars would run up to 40,000 miles (64,000 km) before requiring engine decarbonisation.[13]
Design changes
Engine
Cylinder block a one-piece light alloy casting[14]
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[1]
Oil radiator to maintain a constant 54 °C (130 °F)[14]
Cold viscid oil forced open valves allowing oil into troughs below the big-ends to provide cold-start splash lubrication of the sleeves[14]
Hand-operated oil cleaner
Water pumps on outside of each cylinder bank mounted in tandem with dynamos
This model was usually supplied with a taller and more slender radiator.
Double-Six 40/50 limousine for King George V
Chassis
Grouped chassis lubrication
Back axle incorporating dip-stick cum oiling syringe
Hydraulic shock absorbers
Wheelbase:
Short wheelbase 138 in (3,505 mm) Track 60.0 in (1,524 mm)
Medium wheelbase 147.5 in (3,746 mm) Track 60.0 in (1,524 mm)
Long wheelbase 157.0 in (3,988 mm) Track 60.0 in (1,524 mm)
Prices
Chassis prices: Short £1,100, Medium £1,200, Long £1,350
Short wheelbase standard saloon by Daimler from £1,600
Medium wheelbase limousine by Daimler from £1,900
Long wheelbase limousine by Daimler from £2,300[1]
Cylinder block a one-piece light alloy casting[15]
Double-Six 40/50 with poppet valves
From 1935 to 1938 nine[16] Double-Six 40/50 engines were made with poppet valves - possibly to use surplus components.[1]
Performance
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".[1]
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
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[17][18]
Difficulties
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.[1][19]
Daimler introduced their new Straight-Eight in 1934 and Double-Sixes slipped slowly from the catalogue.[1]
^This information may relate to the second series 30/40 and 40/50 engines with alloy blocks. Pomeroy was in the United States until October 1926 (Douglas-Scott-Montagu & Burgess-Wise 1995, p. 199) and, it appears, could not have designed the first series, which was exhibited to the public that month.
Source: Nixon, St. John C. (1946), "Appendix B: Particulars of all British-built Daimler Cars made from 1897 to 1946", Daimler 1896 to 1946: 50 Years of the Daimler Company, G.T. Foulis & Co., pp. 224–228
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