This engine was designed in the late 1940s and reached production in 1953. The engine was intended to be a ‘big brother’ to the highly successful P6 engine, being primarily intended to fit into the British 7-ton trucks introduced by the major home manufacturers. To aid the export drive of the 1950s the engine was also suitable for the American 5-ton trucks, replacing their standard petrol engines.

The engine had a capacity of 340 cu inches (5.56 litres) and developed 108 BHP at 2700 RPM, substantially above the capability of the P6, with a flat torque curve shape giving 240 Lb.Ft. torque at 1500/1750 RPM. The bore of 4 inches and stroke of 4.5 inches were chosen to keep piston speed down and allow continuous operation at high RPM and a substantial overspeed capability in truck operations. The design of the engine followed typical Perkins practices of the time, using the ‘Aeroflow’ indirect combustion system and CAV in-line fuel pump. Expansion of the production facilities at the Eastfield site were made to cater for the machining of major components and assembly and test alongside the existing P series engines and the new L4 tractor engine.

The engine design and development programme had been accelerated to meet the known demand for this higher power unit, although confidence was high in the engine it soon became apparent that mistakes had been made with the chain drive for the timing train, possibly exacerbated by production changes that were inadequately proven. The resulting problems in the field, where engines were original equipment in trucks produced by Dodge, Commer, Bedford and others, generated major warranty claims as well as losing the Perkins hard-won reputation for reliable products. Coupled to the pressure on the finances of Perkins where a series of plant expansions were being supported, this problem helped to cause a trading loss for the first time since the 1930s and adversely affected the share price of the Company. It was ultimately a major factor in the eventual sale of Perkins to Massey Ferguson in 1959, a situation which might be claimed in hindsight to have been essential to the survival of the Perkins and its prosperity through the 1960s,70s and into the 80s.

It would be unfair to suggest that the R6 was a total disaster. A priority development programme quickly solved the problems of chain vibration and associated component failure, using amongst other techniques high speed photography as an aid to understand the problem. The engine was relaunched in Britain as the R6 Mark 2 at a reduced rating of 104 BHP at 2500 RPM, and later became known as the 6.340, using the nomenclature common to all future engines. The loss of reputation was to prove too great to overcome however and a total of only 33,800 engines were made before production finished in 1962.

However the complete production facility was sold to the new Motores Perkins S.A. associate company which was formed in Brazil in 1959: the engine was produced initially in 6.340 form and was later developed into the 6.357 with an increased bore and timing gears replacing the chain drive. The product continued for many years as a major player in the dieselisation of Brazilian trucks (for Chrysler, GM and Ford) and included export sales to other Latin American countries. Later developments saw the CAV DPA pump fitted and a direct-injection version (6.358) developed. Total production ran into many thousands up to its phase-out in the 1980s.

Meanwhile in England the 6.354 was designed and introduced in 1961, to become the mainstay of six-cylinder production and which benefited from the many lessons learnt on the R6.

In Heritage terms of course, the R6 story does not finish here! Our late colleague and friend, Dereck Lambe, was a collector of all things Perkins (as well as many other things mechanical!) and amongst his huge collection of Perkins engines there was one R6(V). This was the first engine he donated to the Heritage collection and one of our pictures shows this engine the day it was returned to Eastfield. It was in relatively poor condition after years of storage outside, but with the help of the SPA team the engine was renovated to a condition fit for display and it remains today as an important exhibit in the Company’s history.

Article by David Boulton 5.4.2002 and revised 28.10.2010