Editing 4-2-0 (section)

==Overview==
The {{nowrap|4-2-0}} wheel arrangement type was common on [[United States]] railroads from the 1830s through the 1850s. The first {{nowrap|4-2-0}} to be built was the ''Experiment'', later named ''Brother Jonathan'', for the [[Mohawk and Hudson Railroad]] in 1832. It was built by the [[West Point Foundry]] based on a design by [[John B. Jervis]]. Having little else to reference, the manufacturers patterned the boiler and valve gear after locomotives built by [[Robert Stephenson]] of England. A few examples of Stephenson locomotives were already in operation in America, so engineers did not have to travel too far to get their initial ideas.

In England, the {{nowrap|4-2-0}} was developed around 1840 from the [[2-2-2]] design of Stephenson's first [[Long Boiler locomotive]], which he had altered to place two pairs of wheels at the front to improve stability, with the outside cylinders between them.

In the United States, the design was a modification of the {{nowrap|[[0-4-0]]}} design, then in common use. The {{nowrap|0-4-0}} proved to be too rigid for the railroads of the day, often derailing on the tight curves and rapid elevation changes of early American railroads. For the {{nowrap|4-2-0}}, Jervis introduced a four-wheel leading truck under the locomotive's [[smokebox]]. It swiveled independently from the main frame of the locomotive, in contrast to the English {{nowrap|4-2-0}} engines which had rigid frames. The pistons powered a single driving axle at the rear of the locomotive, just behind the [[firebox (steam engine)|firebox]]. This design resulted in a much more stable locomotive which was able to guide itself into curves more easily than the {{nowrap|0-4-0}}.<ref name="White">{{White - History of the American locomotive}}</ref><ref name="Kinert">{{cite book|author =Kinert, Reed|year=1962|title=Early American steam locomotives; 1st seven decades: 1830-1900|url =https://archive.org/details/earlyamericanste00kine|url-access =registration|publisher=Superior Publishing Company|location=Seattle, WA}}</ref>

This design proved so effective on American railroads that many of the early {{nowrap|0-4-0s}} were rebuilt as {{nowrap|4-2-0s}}. The {{nowrap|4-2-0}} excelled in its ability to stay on the track, especially those with the single driving axles behind the firebox, whose main virtue was stability. However, with only one driving axle behind the firebox, the locomotive's weight was spread over a small proportion of powered wheels, which substantially reduced its adhesive weight. On {{nowrap|4-2-0}} locomotives which had the driving axle in front of the firebox, adhesive weight was increased. While this plan placed more of the locomotive's weight on the driving axle, it reduced the weight on the leading truck which made it more prone to [[derailment]]s.<ref name="White"/><ref name="Kinert"/>

One possible solution was patented in 1834 by E.L. Miller and used extensively by [[Matthias W. Baldwin]]. It worked by raising a pair of levers to attach the tender frame to an extension of the engine frame, which transferred some weight from the tender to the locomotive frame and increased the adhesive weight. An automatic version was patented in 1835 by George E. Sellers and was used extensively by [[William Norris (locomotive builder)|locomotive builder William Norris]] after he obtained rights to it. This system used a beam whose fulcrum was the driving axle. On flat and level surfaces, the beam would be slightly raised, but upon starting or on grades, the resistance made the beam assume a horizontal position which caused the locomotive to tip upward.<ref name="White"/><ref name="Kinert"/>

[[File:England loco Birmingham & Glos'ter Railway.jpg|thumb|left|Norris engine for the [[Birmingham and Bristol Railway]]]]
A more practical solution, first put into production by Norris, relocated the driving axle to a location on the frame in front of the locomotive's firebox. This was done because Baldwin refused to grant rights to Norris to use his patented "half-crank" arrangement. [[Cantilever]]ing the weight of the firebox and the locomotive crew behind the driving axle placed more weight on the driving axle without substantially reducing the weight on the leading truck. However Norris's design led to a shorter wheelbase, which tended to offset any gains in [[tractive effort|tractive force]] on the driving axle by reducing the locomotive's overall stability. A number of Norris locomotives were imported into England for use on the [[Birmingham and Bristol Railway]] since, because of the challenges presented by the [[Lickey Incline]], British manufacturers declined to supply.<ref name="White"/><ref name="Kinert"/>

Once [[steel]] became available, greater rotational speeds became possible with multiple smaller coupled wheels. Five years after new locomotive construction began with the [[0-4-0]] ''[[Best Friend of Charleston]]'' of 1831, at the US [[West Point Foundry]], the first {{nowrap|4-4-0}} locomotive was designed by [[Henry Roe Campbell#Locomotive Designer and Builder|Henry R. Campbell]], at the time the chief [[engineer]] for the Philadelphia, Germantown and Norristown Railway. Campbell received a patent for the design in February 1836 and soon set to work building the first {{nowrap|4-4-0}}. Campbell's {{nowrap|4-4-0}} was a giant among locomotives for the time. Its [[cylinder (engine)|cylinders]] were {{cvt|14|x|16|in|mm|0}}, had {{cvt|54|in|mm|0}} diameter driving wheels, a {{cvt|90|psi|kPa}} boiler and weighed {{cvt|12|ST|t|1}}. Campbell's locomotive was estimated to be able to pull a train of {{cvt|450|ST|t}} at {{cvt|15|mph|km/h|0}} on level track, outperforming the strongest of [[Baldwin Locomotive Works|Baldwin's]] 4-2-0s in tractive effort by about 63%. However, the frame and driving gear of his locomotive proved to be too rigid for the railroads of the time, which caused Campbell's prototype to be derailment-prone.<ref name="White"/><ref name="Kinert"/>

As the 1840s approached and more American railroads began to experiment with the new {{nowrap|[[4-4-0]]}} locomotive type, the {{nowrap|4-2-0}} fell out of favor since it was not as capable when pulling a load. {{nowrap|4-2-0s}} continued to be built into the 1850s, but their use was restricted to light-duty trains since, by this time, most railroads had found them unsuitable for regular work.<ref name="White"/><ref name="Kinert"/>

[[File:Est 210 Crampton 187.jpg|thumb|Crampton 4-2-0 built for the ''[[:de:Chemin de fer de l’Est|Chemin de fer de l’Est]]'']]
In England four-coupled and six-coupled engines performed well with freight work. However, the aim for passenger work was greater speed. Because of the fragile [[cast iron]] connecting rods, "singles" continued to be used, with the largest driving wheels possible.

For unclear reasons, British manufacturers did not take up the idea of mounting the forward wheels on a [[bogie]] for some years. There were possibly fears about their stability and with a long rigid frame, greater speed was achieved, albeit at the cost of a very rough ride and damage to the track. The culmination of this approach was seen in the [[Crampton locomotive]] where, to make the driving wheels as large as possible, they were mounted behind the firebox.<ref name="White"/><ref name="Kinert"/><ref name="Comstock">{{cite book|author =Comstock, Henry B.|year=1971|title=The Iron Horse|publisher=Fitzhenry & Whiteside Limited|location=Toronto, Canada}}</ref>