The Story of the 4.99 / 4.107 / 4.108 Engine –the first small Perkins diesel.

Although the early Perkins engines were found suitable for use in the larger cars of the 1930s and ‘40s, they were both too large and too heavy for the post-war vehicles. Frank Perkins did not want to lose the possibility of providing diesel power for the modern cars and vans, so as a consequence in the mid-1950s he asked that the Experimental Department look at making an engine of around 1.5 litres, to produce in the region of 50 BHP at a speed approaching that of contemporary petrol car engines.

The engineers decided that adapting an existing petrol engine to diesel was the most practical and cheapest approach, and so a Morris 1.5 litre engine was obtained and the necessary changes made to produce a diesel prototype. This involved the design of a new cylinder head, the production of an all-welded steel cylinder block and the scheming of a suitable combustion chamber and fuel injection equipment, using initially a CAV in-line fuel pump.

Test bed trials showed that the engine – designated as the Q4 at this stage - would run and produce reasonable power, so the next stage was to install the engine in a Vauxhall car, where it proved to give acceptable performance.

Based on the results obtained from the minimal-outlay approach, the Perkins Board decided that there was potential for such a small engine with possible application too, in typical Perkins fashion, for other markets in the agricultural and industrial sectors. Design work proceeded and a number of innovative features were included in the design of what became the C99 (99 cubic inches capacity and ‘C’for Car). The engine basic design parameters, and particularly its 3.5 inch stroke, were influenced by the limitation of piston speed to 2000 feet/minute based on known technology.

It was decided to use a three bearing crankshaft and wet cylinder liners, with gear timing drive and cast iron cylinder block and head. Instead of the original Perkins ‘Aeroflow’ patented combustion chamber the experimental department opted for a new combustion system patented by a Mr Howard, an Australian engineer best known for the Howard Rotovator. This was an indirect injection design with a spherical chamber part machined in the cylinder head, closed by a special iron insert which formed the lower part of the chamber and also the specially shaped passage to the cylinder. The pintle-type injector was mounted vertically in the cylinder head directly above the insert.

A further important innovation was the introduction of the CAV DPA distributor-type fuel pump, which as well as being cost-effective allowed engine speeds to above 4000 rpm and featured a hydraulic governor providing ‘pull-off’ characteristics suitable for vehicle use.

Considerable test bed and vehicle running proved the design to be sound, with development of the combustion and fuel injection providing clean exhaust and acceptable performance and fuel consumption – important factors for road vehicle use. There were some mechanical problems too, with excessive wear of the skew gears driving the oil pump from the camshaft proving an issue needing specialist help.

The prototype engines were run in a variety of vehicles, including Vauxhall, Ford and Hillman cars, plus other industrial and agricultural applications.

In 1958 the engine was announced, with an opportunity to drive various vehicles being given to customers, press and employees, using the outer periphery of the WW2 airfield at Polebrook, which was being used by the Company at that time for storage and reprocessing of aluminium scrap. In line with the change in engine nomenclature already seen on the 4.270 and 4.192/4.203 engines, the designation of this new little diesel became 4.99 when released into production.

Only 1500 engines were produced in the first year of production, but the engine began to get good publicity, proving that under road conditions fuel consumptions in excess of 50 miles per gallon were possible, and the engine although underpowered in horsepower terms gave good road performance thanks to its superior torque characteristics. Many employees gained experience of the engine in the many conversions of cars undertaken by the Service Garage, these ‘pool’ cars being used for visiting customers and suppliers, service, etc.. The drivers soon became used to driving with the right foot hard to the floor, and the ‘brick-wall’ effect of the governor run-out ensured that engines could not be overly abused! The confusion of service station staff when a driver pulled up to a diesel pump instead of petrol also provided amusement, there were very few diesel cars on the roads in the 1950s!

It wasn’t long before Perkins produced an engine with slightly greater swept volume, the 4.107 having 3.125 inch bore instead of the 3.00 inches of the original engine, giving 107.4 cubic inch capacity and providing greater torque and power, although most engines were used for industrial and marine use at speeds up to 3000 rpm.

Service experience with the 4.99 engine soon showed that there were some problems with the design, especially when the engines were run under the severe conditions found in North American ‘reefer’ units. These were packaged engine and refrigeration units used in truck and railway wagons where they were expected to run for several hundred hours with minimal attention and with high expectation of complete reliability – Mercedes had held a large percentage of the market and Perkins had achieved a breakthrough at their expense. However the 4.99 engines suffered from water leaks from the wet cylinder liners and water pump seals, cylinder head gasket leaks and rapid oil contamination, this latter due to the relatively low operating temperature, extended oil change period and the tendency for the indirect fuel injection system to sludge the lubricating oil with carbon soot.

Perkins quickly developed a revision to the engine, moving to dry liners, ceramic water pump seals and higher oil sump capacity, together with a special large capacity ‘by-pass’ oil filter for the reefer application. Cooperation with the oil industry also resulted in high detergency oil specifications, allowing the oil to carry a greater ‘load’ of carbon particles in suspension without affecting lubricity and viscosity. After a short period when the engine was known as the 4.107DL (dry liner), the designation was changed to 4.108: this became the most popular version of the engine, soon supplanting the other versions. Rated up to 52 BHP at 4000 RPM, the engine was barely competitive with the petrol-fuelled engines of the 1960s and ‘70s in terms of power, but offered excellent pulling characteristics and of course vastly better fuel consumption.

Another problem that bugged the engine throughout its life was the phenomenon of cracking in the area of the bridge between the valves in the cylinder head. Various changes were tried, including change of cast iron specification, ‘tufftride’ heat treatment, Ricardo combustion chambers and additional cooling in the failure area, but all with limited success. Since the cracking did not of itself cause engine failure, service directives were eventually issued advising levels of acceptability!

The 4.108 achieved significant volume sales for vans and light trucks, being fitted as first equipment in Ford Transit, Bedford CF, Commer and other marques – pioneering a breakthrough for the diesel engine into this sector of the market. Significant advantages were claimed, and proved, for economy and reliability. There were however no similar production successes in passenger cars, only Alfa Romeo using the 4.108 in production vehicles in the 1970s.

There were however many engines sold for conversions by garages and private users, especially for taxi use where the economy and long life were appreciated by operators who were willing to forego speed and acceleration for benefits affecting their costs.

A 4.108 engine was installed in a VW transporter (the rear engined ‘buggy’) as a demonstration unit, which impressed VW so much it led to the high volume, three year contract 4.165 (2.7 litre 4 cylinder) business with VW in their LT transporter, before they introduced their own 2.4 litre inline 6 cylinder diesel engine. The 4.165 engines for VW were produced in Hanover, Germany, which is another story.

The 4.107 and 4.108 proved to be very popular in the agricultural markets too, powering in the early 1970s thousands of small combine harvesters in the days when nearly every farmer with arable land had one, made by Claas of Germany and specialist Swiss & Austrian alpine transporters and ‘ladewagons’ achieving no less than 100% of the market with all the manufacturers in these countries, Schilter (CH), Rapid (CH), Aebi (CH), Reformwerke (A) and Lindner (A).

Its short installation length with the three bearing crankshaft, compared to the competition with a five bearing crankshaft, was a sales advantage than won business time and time again.

It was in the marine market that the 4.108 found an enduring niche, providing power for both small craft and also auxiliary power for yachts, the most famous of the latter being Sir Francis Chichester’s round-the-world yacht Gipsy Moth III. The engine’s reliability and economy were prized, as was the availability of service through Perkins distributors virtually anywhere in the world.

The potential for uprating of the engine through turbocharging was tried but never reached quantity production, although some units were sold for aircraft ground power units made by Houchin. A few vehicle engines were made as prototypes and used in Company transport but that was as far as the project went; the product cost started to escalate for the additional parts needed and it was more advantageous to use the 4.154 or 4.165 engines produced in conjunction with Togyo Koyo in Japan. In the 1970s there were moves to upgrade the engine to a slightly larger version (the 4.112) which was successful in prototype form but never saw production.

The 4.99 and 4.108 were in production from 1958 until 1992, the last application being for the auxiliary power unit fitted on British Army tanks in the Gulf War to power the essential air conditioning equipment. A total of almost 500,000 engines were made in Peterborough, with small numbers built elsewhere from kits. The peak production volume was reached in 1970, when almost 30,000 were made. It is interesting to note that the engine remained in production alongside the more modern Prima/500 Series. Quite a record for an engine conceived in the 1950s!

© By David Boulton November 2009, with some sales and applications info input from David Foster.

The Q4 research engine. A 4.99 installed in a Vauxhall Victor

A 1958 Hillmann Minx fitted with a 4.99V engine. A 4.108 as installed in the Alfa Romeo car.

The Gipsy Moth III yacht, August 1966