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 Bentley 4.5 Liter photo

1926 Bentley 4.5 Liter

At the 1919 London Olympia Motor Exhibition, W.O. Bentley debuted the new 3-liter car on Stand 126. Just a few weeks earlier, the prototype engine had been fired up for the first time. The 3.0-liter straight-4 cylinder engine was designed by ex-Royal Flying Corps engineer Clive Gallop and was one of the earliest car engines with dry-sump lubrication, an overhead camshaft and four-valves per cylinder. The four valve single overhead camshaft Hemi design, with the camshaft using a bevel-geared shaft drive, was based on the Mercedes Daimler M93654 racing engine of 1914. Mercedes had displayed one of the winning Grand Prix cars in their London showroom in Long Acre prior to the outbreak of World War I. During the war, W.O. Bentley was commissioned in the Royal Naval Air Service. Determined the engine design may help the British army, the vehicle was confiscated and dismantled at Rolls-Royce. The engine would be very influential on the Rolls-Royce Hawk engine, although with several notable differences, including the fully aluminum enclosed camshaft, and cast-iron monobloc design. Bentley's post-War 3-liter engine would use the Mercedes valve gears and cam drive setup, and would be among the first production cars with two spark plugs per cylinder and twin carburetion. With a bore of 80mm and a stroke of 149mm, the engine offered incredible amounts of low-end torque. Developing approximately 70 horsepower, the 3-Liter could reach speeds of 80 mph. This figure rose to 90 mph for the Speed Models and over 100 mph for the Super Sports.

Production of the 3-Liter Bentley lasted from 1921 through 1929 with 1,622 examples built. It became a legend in motor racing history with its iconic leather-strapped bonnet, classic radiator design, and British Racing Green livery. Early success in the 1922 Isle of Man Tourist Trophy, when Bentleys finished second, fourth and fifth to take the Team Prize, led to the introduction of the TT Replica (later known as the Speed Model).

By the mid-1920s, the competitiveness of the 3-Liter was on the wane and this, together with the fact that many customers had been fitting unsuitably heavy coachwork to the 3-Liter chassis rather than accept the expense of Bentley's 6½-Liter 'Silent Six', led to the introduction of the '4½'.

Using the 3-Liter engine as a base, the 80mm bore and 149mm stroke was enlarged to 100x140mm. The 4 valves per cylinder, 5 main bearing crankshaft, and dual ignition of the 3-Liter were retained. The chassis, transmission, and brakes of the 3-Liter model were employed on the new 4½-Liter model. The chassis, with a length of 172 inches and a wheelbase of 130 inches, was made of steel and reinforced with ties. Although weighing 3,600 lbs and being quite heavy, it was nimble and well balanced. The four-speed gearbox was unsynchronized and the brakes were convention, consisting of 17-inch drum brakes operated by rod and finned for improved cooling. Semi-elliptic leaf springs were placed in the front and the rear.

The engine had two SU carburetors and dual ignition with Bosch magnetos. The racing versions produced 130 horsepower while the road-going versions developed 110 horsepower. Most cars of this ear used two valves per cylinder, but the Bentley engine had four valves per cylinder actuated by a single overhead camshaft. In similar fashion to the 3-Liter engine, bevel gears on a vertical shaft at the front of the engine drove the camshaft.

The 'Blower' Bentleys were basically the same as the Bentley 4½ Litre except with a Roots-type supercharger by engineer Amherst Villiers. W.O. Bentley refused to modify the engine, so instead, the supercharger was in front of the radiator and attached to the end of the crankshaft. The additional weight at the front of the vehicle increased the car's understeer. With the help of the supercharger, the touring models offered 175 horsepower and the racing versions 240 horsepower.

Production of the 4½ Litre cars lasted from 1927 to 1931, with 720 examples produced, including 55 with the supercharger. All but nine (some sources say 8) of the 665 naturally aspirated cars rested on the 'Long Standard', 130-inch wheelbase. The other nine (or eight) rested on a shorter 117.5-inch chassis.

Bentley Motors quickly proved the 4½ Litre's competitiveness by entering the 1927 Le Mans. The original 4½-Liter car, nicknamed by the team 'Old Mother Gun' and driven by Frank Clement and Leslie Callingham, set the fastest race lap of 73.41mph. Unfortunately, their efforts came to an end in the infamous 'White House Crash' pile-up. A 4½ returned the following year and won the event. In 1929, three 4.5-Liters finished second, third, and fourth behind another Bentley, the Speed Six with its larger engine. Other notable finished include a second at the 1930 French Grand Prix and 2nd at the 500 miles of Brooklands.

Despite the incredible success in the salesroom and at the track by all Bentley models, W.O. was forced to sell his company to Rolls-Royce in November of 1931. Like many of companies of the era, it was a victim of the recession that hit Europe following the 1929 Wall Street Crash.


by Daniel Vaughan | Feb 2020

Related Reading : Bentley 4½ Litre History

The Bentley 4 12 liter came into existence to fill a void left by the 3-liter and the 6.5-liter variants. The 3-liter suffered from underperformance while the 6.5-liter was unsafe for the roads. The 6.5-liter was powerful, and with poor road-conditions often caused tires to fail quickly. The solution was the Bentley 4.5-liter a vehicle that had enough power to carry the vehicle down the road at....
Continue Reading >>

1926 Vehicle Profiles

1926 Bentley 4.5 Liter vehicle information

Tourer
Coachwork: Vanden Plas

Chassis Num: 911
Engine Num: 919

The 4½-Litre Bentley made their debut in 1925 and the most famous example was the 'Old Mother Gun' which crashed at Le Mans in 1927. It was repaired and went on to capture Bentley's third LeMans title in 1928, co-driven by the 'Bentley Boys' Woolf Ba....[continue reading]

Tourer by Vanden Plas
Chassis #: 911 


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