THE P6 ENGINE: A DESIGN AHEAD OF ITS TIME.

While the Wolf and Leopard engines of the mid 1930s had put the Perkins Company on the map and demonstrated the practicality of the diesel engine in relatively small trucks and passenger cars, it was the next design conceived by Charles Chapman that was destined to be the most important engine produced in the early years.

Chapman recognised that while more power was required to suit the larger truck chassis of the time, this had to be achieved within the space taken by the current petrol engines and with comparable smoothness and speed. Initial drawing board investigations persuaded him that a six-cylinder engine could be designed using the basic principles proven on the Wolf and Leopard. By cutting allowances to the minimum he calculated the engine would produce power equal to the petrol engines it was hoped to replace, with a similar weight and the advantage of more torque and better fuel economy. By keeping component design simple he believed that mass production methods could be applied, allowing Perkins to do their own machining on comparatively simple tools and thus cut overheads, eliminating outside machinist profits and thus reduce costs.

At a Board Meeting on November 12^th 1936 it was agreed to proceed with the final design and build experimental engines: an improvement in the original ‘Aeroflow’ combustion chamber was to be used and a patent applied for.

The detail design work proceeded so rapidly that at the Board Meeting on 28^th April 1937 (less than 6 months from the agreement to proceed!) Charles Chapman was able to report that the first engine had not only run but was producing the expected performance. Time was clearly running out for the old four-cylinder engines, which were crude in comparison with competitive units now being offered, therefore a decision was taken to order 500 sets of parts without waiting for more proving tests. This may be the first and most critical instance where ‘right first time’ was applied! The Board also sanctioned the design of three and four cylinder versions of the same basic design, the target being to exhibit all three at the London Commercial Vehicle Exhibition in November 1937. This date was achieved, although the 3 cylinder was a mock-up engine with no innards (in fact no P3 was available until 1951!) The engines were originally to be given animal names following the lead of the first engines, however the choice of Panther for the P6 infringed the rights of Phelan and Moore who made the Panther motorcycle. Panther, along with Puma (P4) and Python (P3) were abandoned and no Perkins engines were ’named’ for many years.

The announcement of an engine of under 5 litres rated at 86 BHP and 2600 RPM caused a stir in the industry. The demonstration Commer truck and Studebaker car were much in demand at the Exhibition. Confident of good orders, Perkins arranged the purchase of new machine tools for a machine shop sited in more of the old Barford and Perkins work at Queen Street. The financing was novel, in that Alan Richardson (Frank Perkins brother-in-law), some relatives and friends formed a syndicate to buy the machinery, renting these to the Company until it was in a position to arrange hire-purchase to buy them over a three year period! Orders did begin to come in, but slowly, in spite of attendance at the Brussels and Amsterdam Automobile shows. In the first half of 1938 only 150 P6s were ordered, but the second half brought orders for 385 engines (and a major drop in orders for the Leopard and Wolf). By June 1938 the new engine was being offered in trucks by Albion, Bedford, Commer, Dennis, Dodge, Guy and Thorneycroft. More was to follow as the Seddon brothers, previously conversion agents for Perkins, were convinced enough to design their first vehicle, a 4/5 tonner, around the P6. The creation of Seddon Diesel Vehicles was the start of a long partnership between the two companies.

Through a personal friendship, an opportunity arose with the marine section of the Air Ministry to run the P6 through an Admiralty Type Test at their West Drayton Laboratory.

The engine passed the test and was recommended for use in many light craft where previously no diesel engine had been light enough and powerful enough to replace the petrol engine: the improvement in safety resulting from the less flammable fuel must have contributed greatly during the war years. The engine had to be ‘marinised’ of course, with special sump to allow operation at high angularity to suit both the installation angle needed and the change of attitude as the boat started to plane, as well as the other essential systems modifications.

With war declared in 1939, Perkins was tasked with the production of marine engines, both P6 and S6 (a larger engine which is another story!). During the war years a total of around 5,500 P6s were produced and of these about 3,000 were marine engines.

These engines may have been applied in non-glamorous roles, but they assisted in the saving of many lives by air-sea rescue and other craft throughout the hostilities.

After the war, a speedy planning approval facilitated completion of the Eastfield factory in 1947. Engine production increased prodigiously, keeping pace with engine orders from home and abroad. There was a dearth of suitable engines, so that the P6 found a ready market in conversions as well as new vehicles and industrial equipment.

On the agricultural side many were used in the Fordson E27N tractor as original equipment as well as in the Massey Harris 744 tractor plus many conversion sets. As a result the records show the P6 as being the biggest selling engine for the Company until 1956, when a total of over 39,000 were built.

Although by now the engine was outdated and was being overtaken by the ill-fated R6 and later the 6.354, the creation of the larger bore version, the 6.305 using the new CAV DPA injection pump, helped maintain the engine in production until 1969.

A total of 318,265 P6 engines were made in Peterborough. Of course this was not the end of the story because the Perpetuity Plan for rebuilt engines ensured many units had a second life, and others were produced in overseas locations too.

Even today there are many P6 engines still in use, many in the hands of enthusiasts in vintage vehicles. Without doubt it is the Perkins product which sticks in the memories of many people and which was responsible for the accelerating acceptance of diesel power in the immediate post-war years.

David Boulton May 2002