The K4s quickly endeared themselves to the Scottish crews and, apart from some heavily loaded summer trains, eliminated uneconomic double-heading over the West Highland.
However, as with all Gresley 2-6-0s it could be a rough ride at speed, and a locomotive designed to climb was not suited to the flat straight stretches of the line into Glasgow Queen Street railway station, or the 8.5 miles stretch alongside Loch Eil.
Ride induced vibration was a problem on these stretches, and the middle big-end bearing would require regular nut tightening, with the middle connecting rod dropping off on one occasion: this resulted in increased maintenance inspections.

Crews began to prefer the LNER Class V4, but their lower power restricted their use and the K4s retained their pre-eminence on the West Highland line until the 1947 arrival of the first B1 4-6-0s, which replaced the K4s from Glasgow to Fort William.
These were followed after nationalisation by an influx of Stanier 5MT 4-6-0s and the new K1s, that left the K4s increasingly confined to goods workings.

During the 1950s, the K4s' sphere of operation enlarged and they began to appear at locations such as Edinburgh, Perth, Forfar, Ayr and Tweedmouth.
In 1959 all were concentrated at Thornton in Junction depot in Fife and all were withdrawn in October 1961.
The K4s quickly endeared themselves to the Scottish crews and, apart from some heavily loaded summer trains, eliminated uneconomic double-heading over the West Highland. However, as with all Gresley 2-6-0s it could be a rough ride at speed, and a locomotive designed to climb was not suited to the flat straight stretches of the line into Glasgow Queen Street railway station, or the 8.5 miles stretch alongside Loch Eil. Ride induced vibration was a problem on these stretches, and the middle big-end bearing would require regular nut tightening, with the middle connecting rod dropping off on one occasion: this resulted in increased maintenance inspections.
Crews began to prefer the LNER Class V4, but their lower power restricted their use and the K4s retained their pre-eminence on the West Highland line until the 1947 arrival of the first B1 4-6-0s, which replaced the K4s from Glasgow to Fort William. These were followed after nationalisation by an influx of Stanier 5MT 4-6-0s and the new K1s, that left the K4s increasingly confined to goods workings. 
During the 1950s, the K4s' sphere of operation enlarged and they began to appear at locations such as Edinburgh, Perth, Forfar, Ayr and Tweedmouth. In 1959 all were concentrated at Thornton in Junction depot in Fife and all were withdrawn in October 1961.
LNER Class K4