Daimler Double-Six sleeve-valve V12


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.

The colossus of roads

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. 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 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".
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.

Design

This engine was designed by consultant Chief Engineer L H Pomeroy 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.

7.1-litre Double-Six 50

Engine

Announced 15 October 1926 and observed by The Observer's motoring correspondent to be Britain's first twelve-cylinder car engine.
Power output @ 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 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

Chassis

Announced 1 August 1927. Formed around a pair of 16/55 cylinder blocks
Power output,
Tax rating 31.4 hp

Design change

Production ended in 1932, none with fluid flywheel and pre-selector gearbox.

5.3-litre Double-Six 30/40 or Light Double-Six

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 before requiring engine decarbonisation.

Design changes

Engine
This model was usually supplied with a taller and more slender radiator.
Chassis
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

Double-Six 40/50 with poppet valves

From 1935 to 1938 nine Double-Six 40/50 engines were made with poppet valves - possibly to use surplus components.

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".
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.

Presence

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

Difficulties

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.
Daimler introduced their new Straight-Eight in 1934 and Double-Sixes slipped slowly from the catalogue.

Footnotes

Citations