8th January 2020

Starting with a bang: The Field Marshall Diesel Tractor

What do a sheet of flaming paper, a shotgun cartridge and a hammer all have in common? They’re not murder weapons from a Miss Marple novel, however for anyone familiar with rural life from 1945 onwards, the answer is obvious. They are all necessary items for starting a Field Marshall Diesel Tractor.

The story of this venerable piece of British agricultural history began way back in 1900, when the Yorkshire based engineering firm Marshall’s of Gainsborough made the bold step from steam to internal combustion. As a family owned company, well known for its high quality steam-powered traction engines and farm equipment, the launch of the petroleum-spirit powered ‘Colonial’ tractor units was a bold step into modernity. Fortune is said to favour the bold, however, and the business prospered, with hundreds of these machines being exported to foreign markets. As a result the company grew and expanded rapidly in the new century.

In order to minimise the need for tricky maintenance in the field, Marshall’s moved from the petroleum “Otto Cycle” engines, and drew inspiration from the ‘Hot Bulb’ engine design that had become successful in Europe. Though rudimentary in design, hot bulb units could run on very low-grade fuel oils without losing much power. The combustion of the fuel and air mixture takes place outside of the cylinder itself in a super-heated chamber from which the ignited mixture is drawn into the cylinder by the force of the ignition, driving the piston downwards in either a two or four stroke cycle. Robust and simple, once started, a hot bulb engine can run constantly for as long as it has fuel.

Marshall’s evolved this rudimentary engineering into a simple but effective two-stroke diesel unit for their tractors, one which took inspiration from this lack of mechanical complexity. Fitted to its latest tractor, called the Field Marshall, the engine was launched into a post-war landscape in real need of new agricultural technology. The two-stroke diesel unit was efficient and strong, more flexible than its outdated predecessor, but equally unbreakable in nature. Thanks to these upgrades, when the Field Marshall was unveiled to the public in 1945, it was hailed for its power, its simplicity and its robustness.

Although a sales success, it was not without its quirks however. In particular, its starting procedure took some practice and was a direct hang-over from the older engines. A farmer had first to pre-heat the cylinder with a flaming taper. The lit wick had to be inserted into the cylinder head and left to heat the metal to the point at which the fuel could ignite. While the metal reached temperature, a blank shotgun cartridge had to be fitted into a breech on the intake manifold, and covered with a steel cap. Once the required time had passed and the engine was hot enough to run, with a strong blow from a hammer the cartridge would be fired into the engine creating enough detonation to move the piston through its first full stroke. As it came to life, it produced a clatter that only a 6 litre two-stroke diesel engine could produce, loud, slow and unique.

This lengthy process meant that once running, many farmers would avoid switching the engines off wherever possible. The weighty “thump” of the large engine at tickover led to the second characteristic of the Field Marshall tractor – its ability to shake itself into muddy ground in minutes. Many owners experienced returning to machines that had sunk to their axels in mire, needing teams of men, horses and other tractors to free these stricken beasts from their self-dug graves.

These quirks aside, the Field Marshall’s reputation for bombproof engineering meant that they remained a huge part of British agricultural life and were a familiar site on farms for decades after production ceased in 1957.

Have you ever started a Field Marshall with a hammer, or do you remember them from your youth? If so, share your experiences with us in the comments below.

In the sixties, there were many Field Marshall tractors in regular use in the Terai belt of the then Uttar Pradesh in India. I remember the thump of the Field Marshalls and Lanz Bulldogs. We owned a 1950s model German made Richter two-cylinder tractor and I remember it had to be started using two burning tapers, one each, screwed into each cylinder head. A decompression lever and a strong arm were what it took to get the engine to life.

OTI, 29/03/2021

Seem to recall you placed a wheel in a groove on the flywheel which was linked to a decompressor? Then you spin the flywheel and whip the handle out just before the wheel drops off the groove! It might have been combined with the cardboard taper in the cylinder head? I also had the pleasure of borrowing a Lanz Bulldog which was a true hot bulb engine. This had a separate petrol tank, spark plug battery and trembler coil. You spun the flywheel 3/4 of a Rev, using the steering wheel and column, backwards to bounce of compression/petrol bang and then it would go through the next TDC and start to run. There was a dial on the nacelle which indicated forward and reverse. Once hot you switched fuels to diesel (a bit like the E27N) and turned off the trembler. To reverse you killed the revs and caught the piston bouncing off TDC so starting the engine in reverse - took practice!

Greygreaser, 19/03/2021

I seem to remember that if the cranking speed was insufficient at the moment of ignition, the engine would bounce at tdc and run backwards. .. three reverde and one forward gear. Quite frightening to crank as a young apprentice I seem to remember. Two people on the crank handle were a safer bet.

Seer, 10/03/2021