W.O. Bentley's first vehicles were powered by a four-cylinder engine with a four-valve head and a three-liter displacement. They earned Bentley two Le Mans victories and helped establish the reputation of the company. However, to remain competitive and to be able to carry heavy and luxurious coachwork, the size of the engine and number of cylinders needed to increase. To this end, he began creating a six-cylinder version of the existing engine. The resulting six-cylinder engine was basically the existing four-cylinder unit with two additional cylinders and a displacement of 4.5 litres. While road-testing a prototype in France in 1924, W.O. happened upon a Rolls-Royce prototype that was also undergoing tests. A race quickly ensued and when it was over, W.O. Bentley was convinced that his new flagship needed more performance. The result was the 6 1/2 Litre which may have brought about the demise of the company even further, as it was Rolls-Royce that purchased a bankrupt Bentley early in the Depression, for the purpose of removing it as a competitor.
In period, the 6.5 Litre was known as the Big Six. Its engine was a development of Bentley's three-liter powerplant. First shown at the London Motor Show of 1925, these cars were with customers by March 1926. During its production lifespan over a five year period, a total of 545 examples were built. 362 were the 'Standard' 6½ Litre and 182 were Speed Six specification.
The engine in the 6 1/2 Litre had four tulip-shaped valves per cylinder and was fed by a single Smiths updraught carburetor. The overhead camshaft was driven by two small eccentrics coupled to triple connecting rods, the drive for which came from a helical gear at the rear of the crankshaft. The crankshaft was a multi-disc torsional damper, the compression ratio was 4.4:1, and the ignition was by two magnetos (later coil and single magento) which fed a pair of sparking plugs per cylinder. There was a single-plate clutch and a modified gearbox with notably high ratios. The third gear had a ratio of 1.278:1 which was the highest ever used in a standard W.O. Bentley.
The chassis was given one tubular and four pressed-steel cross members for additional rigidity and strength. The suspension was comprised of semi-elliptic leaf springs at all four corners, for which there were three specifications depending on the chosen wheelbase and type of body. There were three different wheelbase sizes making the 6.5 Litre a very versatile vehicle capable to accommodate a wide range of customer requests and needs. Braking was mechanical to all four wheels. The steering was by worm and wheels and the damping was by Bentley and Draper Duplex or Hartford Duplex.
Top speed was achieved at 3,500 rpm and 84 mph. In 1926, the chassis alone cost circa £1,450 to £1,575, while that of a complete car would have been in excess of £2,000.
The 6½ Litre model spawned the Speed Six, which is said to have been W.O.'s favorite among all the illustrious motorcars he created. Introduced in 1928, it would become the most successful racing Bentley. Modifications included a high-performance camshaft, a compression ratio of 5.3:1, a single-port block, and two SU carburetors. The most popular of the three wheelbase sizes was the smaller 138 inch platform. The other sizes included a 140.5- and 152.5-inch size.
Perhaps the most famous of the Speed Six was the Blue Train Bentley which Woolf Barnato raced in March of 1930 against the Blue Train. The vehicle wore H.J. Mulliner saloon coachwork. by Daniel Vaughan | Aug 2019
Related Reading : Bentley 6½ Litre History
The Bentley 6.5 Litre was a continuation of the Litre series Walter Owen Bentley had created. The four-cylinder 4.5-liter unit used in the 4½ Litre was used for the 6½ Litre Bentley but the 6½ Litre Bentley had two extra cylinders. The Bentley stright-6 had a cast-iron block and head with an overhead camshaft having four-valves per cylinder. There were two spark-plugs per cylinder. The 100 mm bore.... Continue Reading >>
Related Reading : Bentley 6½ Litre History
The Bentley Company was created by Walter Owen and Henry Bentley in 1919. Within a few years they had their first 24 Hours of LeMans victory. The company prospered for a number of years before going into receivership in 1931. The company had created a total of 3033 cars and had won victories at LeMans five times. The litre series engines began in 1919 with the four-cylinder 3-litre unit..... Continue Reading >>
The Bentley 6 1/2 Litre brought the company back-to-back LeMans victories in Speed Six specification. The Big Six, as the 6 1/2 was referred to in period, was an evolution and development of Bentley's three-liter engine. It was designed to carry heav....[continue reading]
In order to compete with Rolls-Royce, W.O. Bentley designed a large capacity, 6-cylidner engine for a longer chassis and more luxurious coachwork than his five-year-old 3 Litre cars. But he was short on cash, and it was expensive to produce so, in 19....[continue reading]
This powerful Bentley 6.5 litre was delivered new to Lady Cholomondley in England in 1926 and thence to a succession of owners until it was found abandoned in Rhodesia in 1960. It was restored in 1972 and then had several additional owners until it w....[continue reading]
This 3 Litre Bentley is thought to be one of only two unrestored and completely original tourers from the heady days of the W.O. Bentley era. The first owner of this 3 Litre was a young eningeer named Clive Gallop. Gallop is an important figure in Be....[continue reading]
Salon Privé Bentley Masters to celebrate Bentleys Centenary year in style with 3 very special models previously owned and commissioned by Bentley Boy and Bentley Motors Limited Chairman, Captain Woolf Barnato
One-of-a-kind 1930 4 ½-litre Blower...
Bentley celebrates its Centenary in 2019
World-famous Mille Miglia thousand-mile race first ran in 1927
Bentley Blower was due to become first British car to compete in 1930
2019 marks 89 years since Birkin and Barnatos aborted attempt
Iconic racing Bentley of pre-war years
Ground-breaking 4½ Litre model forever linked to dashing Bentley Boy Sir Henry Tim Birkin
Supercharged engine dramatically boosted power of late 1920s car
Blowers legendary performance broke Brooklands...
Historical Bentleys star at prestigious Edinburgh event
1952 R-Type Continental, Blue Train and 8 Litre among line up
Bentley Sunday highlights best of British brands historic range
(Crewe, 31 August) Scotlands historical seat of pow...
Famous heritage models hit international classic show circuit
95 years of history to tour from Goodwood to Pebble Beach
85th anniversary of Blue Train race and 1930 Le Mans win
(Crewe, 21 May 2015) Legendary cars from Bentleys past are...