In 1883, the extension of the Cape Government Railways (CGR) Eastern System's line from Queenstown reached Sterkstroom and passed through the Stormberg coalfields, where the Molteno and Cyphergat collieries were operating.
While the Colonial coal was much cheaper than imported Welsh coal, it had a non-combustable content of as high as 29%, which led to difficulties when it was used in locomotives since it frequently caused train delays due to stops to allow the stokers to clear the grate of clinker and ash.

Tests were carried out to compare the results obtained from the use of the sea-borne Merthyr coal, which was available at East London for use on down or inland journeys, and the Stormberg coal, which was used on the up or coastward return journeys.
It was found that the average fuel consumption on a return journey using Stormberg coal was 63.35 pounds (28.7 kilograms) per train-mile, compared to 31.67 pounds (14.4 kilograms) per train-mile when using imported Merthyr coal.

In attempts to overcome the problem, John D. Tilney, the Eastern System's Locomotive Superintendent, carried out many experiments on some of the 4th Class locomotives which had entered service on the Eastern System in 1880 and 1882.
The most significant of these experiments involved modifying the boilers and frames to accommodate oscillating firebars and larger fireboxes.
In 1883, the extension of the Cape Government Railways (CGR) Eastern System's line from Queenstown reached Sterkstroom and passed through the Stormberg coalfields, where the Molteno and Cyphergat collieries were operating. While the Colonial coal was much cheaper than imported Welsh coal, it had a non-combustable content of as high as 29%, which led to difficulties when it was used in locomotives since it frequently caused train delays due to stops to allow the stokers to clear the grate of clinker and ash.
Tests were carried out to compare the results obtained from the use of the sea-borne Merthyr coal, which was available at East London for use on down or inland journeys, and the Stormberg coal, which was used on the up or coastward return journeys. It was found that the average fuel consumption on a return journey using Stormberg coal was 63.35 pounds (28.7 kilograms) per train-mile, compared to 31.67 pounds (14.4 kilograms) per train-mile when using imported Merthyr coal.
In attempts to overcome the problem, John D. Tilney, the Eastern System's Locomotive Superintendent, carried out many experiments on some of the 4th Class locomotives which had entered service on the Eastern System in 1880 and 1882. The most significant of these experiments involved modifying the boilers and frames to accommodate oscillating firebars and larger fireboxes.
CGR 4th Class 4-6-0TT 1884