4-10-2

Front of locomotive to the left

NGR Class C Reid Ten-wheeler no. 171, later SAR Class H no. 253

Under the Whyte notation for the classification of steam locomotives by wheel arrangement, 4-10-2 represents the arrangement of four leading wheels on two axles, usually in a leading bogie, ten powered and coupled driving wheels on five axles, and two trailing wheels on one axle, usually in a trailing truck. In South Africa, where the wheel arrangement was first used, the type was known as a Reid Tenwheeler. In the United States of America (USA) it was known as a Southern Pacific on the Southern Pacific Railroad and as an Overland on the Union Pacific Railroad.

Other equivalent classifications are:

• UIC classification: 2'E1' (also known as German and Italian classifications)
• French classification: 251
• Turkish classification: 58
• Swiss classification: 5/8

Overview

This wheel arrangement was first used on the Natal Government Railways (NGR) in South Africa in 1899, on a 4-10-2T tank locomotive that was designed to meet the requirement for a locomotive that could haul at least one and a half times as much as an NGR Dübs A 4-8-2T locomotive.

In the USA a simple expansion (simplex) version of the type was used only on the Southern Pacific and Union Pacific Railroads. Baldwin Locomotive Works built an experimental compound expansion 4-10-2 in 1926, but since the weight and length of this engine was too much for all but the heaviest and straightest track and compound steam locomotives had already lost favor on US railroads, its demonstration runs failed to generate interest and no more were produced.

Usage

Brazil

Brazil had meter-gauge 4-10-2 tender locomotives built by Henschel in 1936. These were converted to 1600mm gauge in 1940.

South Africa

Between 1899 and 1903 the Natal Government Railways (NGR) placed one hundred and one 4-10-2T tank locomotives in service. The locomotive was designed by G.W. Reid, the Locomotive Superintendent of the NGR at the end of the nineteenth century, and built in Scotland by Dübs and Company and the newly established North British Locomotive Company. On the NGR the locomotive type became known as the Reid Tenwheeler and was officially designated Class C.

The locomotive used saturated steam and was equipped with Allan straight link valve gear. The trailing Bissel truck was of the Cartazzi type that allowed the axle some lateral movement. In order to negotiate sharp curves, both the first and fifth sets of driving wheels were flangeless, but since the blind trailing drivers had a tendency to derail while reversing, particularly over points, their tyre width was later increased from to . In 1912, upon the establishment of the South African Railways, the surviving unmodified NGR locomotives were designated Class H.

In 1901 and 1902, towards the end of the South African War, the Imperial Military Railways also acquired thirty-five Reid Tenwheeler locomotives from Dübs and Company and Neilson, Reid and Company. After the war they came onto the roster of the Central South African Railways (CSAR), who designated them Class E. In 1903 the CSAR modified six of them to 4-8-2T tank locomotives and, beginning in 1905, the remainder to 4-8-0TT tank-and-tender locomotives.

A final order for one new Reid Tenwheeler was placed by Witbank Collieries as late as 1927. The total of 137 locomotives built to this design was about double the number of all other 4-10-2 locomotives in use elsewhere in the world, all of which were tender locomotives that served mainly in the United States of America and Brazil.

United States of America

In the US, the type was used only on the Southern Pacific Railroad (SP) which called it the "Southern Pacific", and the Union Pacific Railroad (UP) which called it the "Overland" after their corporate sobriquet, "The Overland Route". Only sixty locomotives of this wheel arrangement were built for domestic service and all but one were constructed as simplex three-cylinder engines.

In 1925 the SP placed an order for sixteen 4-10-2 locomotives with the American Locomotive Company (ALCO) and, later in the same year, the UP ordered one. The first SP locomotive, no. 5000, was completed in April 1925, while the UP locomotive, no. 8000, was completed the following month. Within a few months the SP ordered more of these engines and built up a fleet of 49. The UP, on the other hand, waited thirteen months before repeating orders and establishing a fleet of ten 4-10-2 locomotives. All 59 were simplex locomotives and were built by ALCO.

Baldwin 60000 in the Franklin Institute Science Museum

In 1926 Baldwin Locomotive Works constructed an experimental demonstrator, the Baldwin 60000, which was a three-cylinder compound locomotive, the only 4-10-2 so constructed. This engine used high pressure steam in the inside high pressure cylinder and then exhausted that steam into the two low pressure outside cylinders. It also had a water tube boiler, one of a very few locomotives so equipped in the United States. As technologically innovative as Baldwin's 4-10-2 was, however, it was outmoded when built since compound steam locomotives had already lost favor in US railroading.

It was found that the 4-10-2 type ran better and rode smoother than the 2-10-2 type from which it had evolved. The third cylinder in the center of the cylinder saddle sloped down at a 9½ degree angle to a crank on the second drivers' axle, while the two outside rods connected to the third drivers. The three cylinder feature on these locomotives gave them a distinctive sound at work, described as a "hop, skip and jump rhythm".

While the SP engines could operate only on relatively straight and heavily built main lines, their long service lives of between 28 and 30 years proved that they were good locomotives. The most serious mishap was when, in November 1946, one of the SP 4-10-2 locomotives suffered a boiler explosion which killed four train crew. However, the inside cylinder’s rod created serious maintenance problems because the floating bushings failed, which lengthened maintenance down-time since such failures required major valve re-settings that caused delays. It was reported that such failures created such great pounding on the rails that railroad housewives along the line "complained of crockery cracking when a defective 4-10-2 rumbled past their homes".

When the UP became tired of the major mechanical problems associated with three cylinders, it converted its locomotives to two-cylinder locomotives in 1942 and renumbered them 5090 to 5099.

Two locomotives of this type have been preserved:

• Southern Pacific 5021, on static display at the Los Angeles County Fairgrounds in Pomona, California.
• The Baldwin 60000 demonstrator, as a moving display at the Franklin Institute Science Museum in Philadelphia, Pennsylvania.