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 12th 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.
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.
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
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