Daimler Double-Six sleeve-valve V12

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 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)

• Chassis prices: Type O £1,850, Type P £1,950, Type W £1,950
• Standard saloon de luxe by Daimler £2,450
• Standard enclosed limousine by Daimler £2,800[1]

Petrol was lifted to a reservoir by the engine from the rear-mounted tank by Autovac[9]

• Wheelbase:

Type Q wheelbase 131 in (3,327 mm) Track 52.0 in (1,321 mm)

Type M wheelbase 141.0 in (3,581 mm) Track 52.0 in (1,321 mm)

Type V wheelbase 142.0 in (3,607 mm) Track 54.0 in (1,372 mm)

Type O wheelbase 145.0 in (3,683 mm) Track 60.0 in (1,524 mm)

• Tyres:

5.25 in (133 mm) x 31 in (787 mm) on the coupé tested by The Times[8]

• Dimensions of standard saloon:

Length 190 in (4,826 mm)

Width 65 in (1,651 mm)

Height 72 in (1,829 mm)

• Chassis prices:
• Standard saloon by Daimler £1.300

Production ended in 1932, none with fluid flywheel and pre-selector gearbox.[1]

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 130 °F (54 °C)[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)

• 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]

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]