The Story behind the Bentley

Seen from a twenty-first century perspective, the Derby Bentley could be seen as a genetically-modified Rolls-Royce. Read on.

The story begins with the Depression brought about by the Wall Street crash. This had a damaging effect on the luxury car market, and consequently Rolls-Royce’ thoughts turned towards the design of a new small car, but with the same level of luxury and refinement as was provided by the 20/25 model. With this in mind a completely new car was designed, code-named ‘Peregrine’. This had a new engine of about 2.5 litres capacity, and capable of carrying up to four passengers. Although the car performed and handled well on test during 1932 the feeling was that it would not be possible to produce the car at a price that would appeal to the market for which it was intended without compromising its’quality.

In parallel with this, Rolls-Royce acquired the ailing Bentley Motors in November 1931. Bentley had been badly affected by the collapse of the luxury car market, and neither their 8-litre chassis nor the 4-litre was able to restore their fortunes. Although making good publicity and promoting the Bentley name, their racing programme had been very costly which further weakened the company. Rolls-Royce’ old rival Napier, who had last produced a car in 1925, cast covetous eyes on Bentley Motors. In a strategic move to prevent Napier from returning to the car market Rolls-Royce stepped in and bought Bentley Motors, including the services of W O Bentley. A new company Bentley Motors (1931) Ltd was then formed.

Whether the purchase of Bentley Motors was purely an interventionist move or whether at the outset Rolls-Royce intended to produce a car with the Bentley name is not certain. However, before long Royce decided that there was an opportunity not to be missed; a debate ensued as to how the Peregrine could be reconfigured as a car worthy to carry the Bentley name. Supercharging either the original or a redesigned Peregrine engine was considered, but ultimately discounted on grounds of reliability. Meanwhile a derivative of the 20/25 engine had been developed: the J1. This had a cross-flow cylinder head, equipped with six inlet ports, a modified camshaft and twin SU carburettors. In October 1932 it was agreed after much debate that the J1 engine mated to the 20/25 gearbox would be fitted in the Peregrine chassis. The result of this was known as ‘Bensport’, and became the Bentley 3 1/2L. To accommodate the larger engine and gearbox the wheel base of the Peregrine chassis had to be increased from 120” to 126”.

The first Bentley 3 1/2L was revealed to the Press at the end of September 1933. This followed twelve months of intensive development and testing during which many improvements were made to the original concept. It received enthusiastic reviews from the motoring press, and was displayed to the public at the 1933 Motor Show at Olympia. The proportions of the car were the ideal basis for very elegant coachbuilders designs and this was demonstrated at the Olympia. This became one of the hallmarks of the Derby Bentley, and throughout its production it gave rise to a number of stunning body styles.

Another characteristic of the car was captured early in 1934, when it attracted the title ‘The Silent Sportscar’. Earlier Rolls-Royce had expressed concern during the development of the car that it was too smooth, and would be compared with the 20/25 – “The car must have a sports harshness…” However the final combination of performance with refinement became a major selling point.

Another departure from Company policy was the (unofficial) involvement in racing. Not since 1906, when a Rolls-Royce Light 20 competed in the Isle of Man TT had the Company been involved in motor racing. However in 1934 they supported the private entry of Eddie Hall in the Ulster TT. This enabled some further testing under extreme conditions of various modifications that were being considered. Hall continued to race a Derby Bentley, competing in the 1936 Ulster TT. An entry at Le Mans for that year had been accepted, but the race was cancelled. However it did run at Le Mans in 1950, and finished a very creditable eighth.

In 1936 an enlarged engine was offered, to cope with the increasing body weight. This was the 4 1/4L engine, and almost immediately was adopted as standard. This continued the success of the 3 1/2L, but weaknesses in the crankshaft bearings were revealed. The extra loading imposed by the larger capacity coupled with the ability to drive at high speed continuously on the new autobahnen and autostrada caused premature bearing failure. The problems were not cured until extensive changes had been made to the crankshaft oiling system, coupled with the introduction of new bearing materials.

Engine and chassis developments continued, and in 1937 a change to the combustion chamber resulted in a lower compression ration but improved cylinder filling and combustion. However it was found that the resulting power curve continued to rise as it passed through the maximum safe rev limit of 4,500 rpm. In 1938 the final development of the 4 1/4L chassis was produced. This had a modified camshaft; the lift was increased a little, but the timing altered to give a power curve that dropped away above 4,000 rpm. However a higher final drive was introduced; this was achieved by making fourth gear an over-drive, and altering the axle ratio. Thus the M-series cars were created.