Editing Field Marshall (section)

==Field-Marshall tractor==
[[File:1950 Field Marshall.jpg|thumb|1950 Model]]

The Field-Marshall and its [[Track Marshall]] tracked stable-mate (Marshall-engined '''Fowler VF''' and '''VFA'''), were distinctive because of the use of a single-cylinder two-stroke diesel engine (of about 6-litre capacity) coupled to a very large [[flywheel]], whereas tractors such as the [[Fordson tractor|Fordson N]] used a multi-cylinder engine. This single-cylinder design was quite common in Europe at the time, the [[Lanz Bulldog]] being another example. The Lanz, though, used a [[hot bulb engine]].

=== Field-Marshall timeline ===
* Field-Marshall Series 1   - 1945–1947 - 6&nbsp;mph and 9&nbsp;mph gearboxes available - Mark I & II variants
* Field-Marshall Series 2   - 1947–1949 - 6&nbsp;mph and 9&nbsp;mph gearboxes available - Mark I & II variants
* Field-Marshall Series 3   - 1949–1953 - 12&nbsp;mph high and low gearbox
* Field-Marshall Series 3A  - 1953–1957 - 12&nbsp;mph high and low gearbox

===Starting===
[[File:Flywheel and decompressor, Field-Marshall tractor, Cophill Farm vintage rally 2012.jpg|thumb|Flywheel and decompressor lever]]

To start the Marshall a smouldering piece of special paper, containing [[Sodium nitrate|saltpetre]], is inserted into the cylinder head by means of the special screw-in holder in the cylinder head (this smouldering paper acts as a [[Glow plug (diesel engine)|glow plug]]).

The engine is then turned over with a starting handle placed in the starting dog on the flywheel. This is aided by the decompression valve, which decompresses the engine and makes it easier to turn over to allow the flywheel to gain speed and momentum to turn the engine through compression, and get the engine to fire. A spiral groove on the perimeter of the flywheel carries a wheel on the  decompressor mechanism and is used to determine the number of revolutions before the decompressor disengages. This is generally up to three revolutions, but can be anything up to six revolutions.<ref >{{Cite patent|country=US|number=1990427
  |title=Means for starting compression ignition oil engines 
  |inventor1-first= Samuel Horace|inventor1-last= Wright Dawson   
  |assign1=[[Marshall, Sons & Co.]]
  |pubdate=1935-02-05 
}}</ref> Depending on the condition of individual tractors, it may need considerable physical exertion to start a Marshall.

[[File:Starting cartridge breech, Field-Marshall tractor, Cophill Farm vintage rally 2012.jpg|thumb|Starting cartridge breech]]

A cartridge starting system is also fitted to the tractor. A [[shotgun shell|shotgun type]] blank cartridge is loaded into a breech on the engine's intake system. The smouldering paper is placed in the cylinder head, and the cartridge is fired by tapping the base of the protruding firing pin with a hammer. This puts a charge into the bore, sending the piston through its stroke, bursting into life. This method, however, deposits carbon which often causes jamming of the decompression valve if cartridges are regularly used. It also puts significantly more strain on the engine.

Later versions of the Field-Marshall had more sophisticated starting systems available; electric starters were optional on the Series 3As.

===Applications===
The Field-Marshall tractors were commonly used to pull [[agricultural machinery]] such as [[threshing machine]]s from site to site. Once in place, the Field-Marshall would be used as the powerplant for the threshing machine, the tractor's belt pulley coupled by a large flat drive belt to the threshing machine's pulley.

Field-Marshalls with tracks were produced under the [[John Fowler & Co.|Fowler]] brand name, being converted in the Fowler factory at [[Leeds]]. The first were designated the "Fowler VF", later ones being "VFA"s.