1923 Bentley 3/4½-Litre Supercharged Birkin-era 'Old Mother Gun' Replica

Footnotes

With characteristic humility 'W O' was constantly amazed by the enthusiasm of later generations for the products of Bentley Motors Limited, and it is testimony to the soundness of his engineering design skills that so many of his products have survived. From the humblest of beginnings in a mews garage off Baker Street, London in 1919, the Bentley rapidly achieved fame as an exciting fast touring car, well able to compete with the best of European and American sports cars in the tough world of motor sport in the 1920s. Bentley's domination at Le Mans in 1924, 1927, 1928, 1929 and 1930 is legendary, and one can only admire the Herculean efforts of such giants as Woolf Barnato, Jack Dunfee, Tim Birkin and Sammy Davis, consistently wrestling the British Racing Green sports cars to victory.

W O Bentley proudly unveiled the new 3-litre car bearing his name on Stand 126 at the 1919 Olympia Motor Exhibition, the prototype engine having fired up for the first time just a few weeks earlier. Bentley's four-cylinder 'fixed head' engine incorporated a single overhead camshaft, four-valves per cylinder and a bore/stroke of 80x149mm. Twin ML magnetos provided the ignition and power was transmitted via a four-speed gearbox with right-hand change. The pressed-steel chassis started off with a wheelbase of 9' 9½" then adopted dimensions of 10' 10" ('Standard Long') in 1923, the shorter frame being reserved for the TT Replica and subsequent Speed Model. Rear wheel brakes only were employed up to 1924 when four-wheel Perrot-type brakes were introduced.

In only mildly developed form, this was the model that was to become a legend in motor racing history and which, with its leather-strapped bonnet, classical radiator design and British Racing Green livery, has become the archetypal Vintage sports car.

Early success in the 1922 Isle of Man Tourist Trophy, when Bentleys finished 2nd, 4th, and 5th to take the Team Prize, led to the introduction of the TT Replica (later known as the Speed Model) on the existing 9' 9½" wheelbase, short standard chassis.

However, by the middle of the decade the 3-Litre's competitiveness was on the wane and this, together with the fact that too many customers had been tempted to fit unsuitably heavy coachwork to the excellent 3-Litre chassis rather than accept the expense and complexity of Bentley's 6½-litre 'Silent Six', led to the introduction of the '4½'.

The new 4½-Litre model effectively employed the chassis, transmission and brakes of the 3-Litre, combined with an engine that was in essence two-thirds of the six-cylinder 6½-litre unit. Thus the new four-cylinder motor retained the six's 100x140mm bore/stroke and Bentley's familiar four-valves-per-cylinder fixed-'head architecture, but reverted to the front-end vertical camshaft drive of the 3-Litre. Bentley Motors lost no time in race-proving its new car. It is believed that the first prototype engine went into the 3-Litre chassis of the 1927 Le Mans practice car. Subsequently this same engine was fitted to the first production 4½-Litre chassis for that year's Grand Prix d'Endurance at the Sarthe circuit.

The original 4½-Litre car, nicknamed by the team 'Old Mother Gun' and driven by Frank Clement and Leslie Callingham, promptly set the fastest race lap of 73.41mph before being eliminated in the infamous 'White House Crash' multiple pile-up.

Bentley made approximately 1,600 3-Litre models (513 to Speed Model specification), the majority of which was bodied by Vanden Plas with either open tourer or saloon coachwork. The example offered here was built on the short standard 9' 9½" wheelbase chassis. Dr Clare Hay does not list a coachbuilder for '216', which left the factory fitted with engine number '217'and was delivered new to a Mrs Gilbey in April 1923. The subsequent fitting of Whitehead four-wheel brakes is noted.

The chassis number cannot be confirmed but there is correspondence on file from Julian Ghosh (renowned engineers) that it is '216' (a 3-Litre chassis). Creating a 'Blower' involves the removal of the two pieces of chassis frame that are stamped with its identity, so these are no longer part of the car.

Seemingly the engine has been rebuilt around the crankcase of 'SM3906', incorporating Phoenix con-rods, Cosworth pistons, and twin Bosch magnetos. 'SM3906' started life in 'SM3901', which was the first production 4½-Litre Supercharged chassis, registered 'GF 776'. Dr Hay states: "Last recorded owner 1938. Front dumb irons on 3 Litre ch. DE 1207. Parts in other cars."

This car's other notable features include hydraulic braking, Zeiss lamps, and a four-branch stainless steel exhaust complete with Brooklands-style 'can'. There are many notes on file detailing works carried out by engineers John Guppy and Adrian Butt, and some work by Clive Oliver. The coachwork was built by Specialist Welding & Fabrication of Okehampton in 2005.

Finished in blue livery with matching interior trim, this beautifully turned out car is yet another project completed by Malcolm Bishop to his personal specification and to the standards we have come to expect. It should be noted that the Lot is offered with a photocopy of the original history file and that the personal registration is being retained; it is expected that a new V5C document will have been issued by time of sale.