Portable engine different from traction engine
Alexander Dean of Birmingham
Ransomes of Ipswich
William Tuxford and Sons of Boston, Lincolnshire
Howden of Boston, Lincolnshire
Clayton & Shuttleworth of LincolnThis last manufacturer is particularly noteworthy here. The first Clayton & Shuttleworth portable was built in 1845, a two-cylinder engine. In 1852, the company won a gold medal for a portable engine at the Royal Agricultural Society's Gloucester show, and thereafter the business expanded rapidly: they established a second works, in Vienna in 1857, to target the European market, and by 1890 the company had manufactured over 26,000 portable engines, many being exported all over the world.In the 1850s, John Fowler used a Clayton & Shuttleworth portable engine to drive apparatus in the first public demonstrations of the application of cable haulage to cultivation.
In parallel with the early portable engine development, many engineers attempted to make them self-propelled – the fore-runners of the traction engine. In most cases this was achieved by fitting a sprocket on the end of the crankshaft, and running a chain from this to a larger sprocket on the rear axle. These experiments met with mixed success.
As noted early on by Thomas Aveling (later of Aveling & Porter fame), it was absurd to use four horses to pull a steam engine from job-to-job, when the engine possessed ten times the strength of the horses. It was therefore inevitable, once self-propelled traction engines had become sufficiently reliable, that they would take over the roles of many portable engines, and this indeed started to happen from the late 1860s. In the UK this development was perhaps somewhat delayed by various acts of parliament that limited the use of steam powered vehicles on roads. Portable engines, being horse drawn, faced far fewer restrictions.Other builders manufactured engines around the world.  Small
machine shops could assemble units with a small engine and vertical
boiler and put it on wheels. In North America dozens of builders
entered the market—Case, Sawyer Massey, and Gaar Scott for example.
Native builders erected engines in France, Italy, Sweden and Germany.
However, the portable engine was never completely replaced by the traction engine. Firstly, the portable, having no gearing, was markedly cheaper, and secondly, numerous applications benefitted from a simple steam engine that could be moved, but did not require the additional complexity of one that could move itself.
Small numbers of portables continued to be built even after traction engine production ceased.  Robey and Company of Lincoln were still offering portables for sale into the 1960s. The English builders produced in the order of 100,000 portable steam engines in the hundred year time period both for home use and export abroad.
From about 1900 onward, the requirement for a small cheap source of power on farms was increasingly taken over by internal combustion engines, such as hit-and-miss engines and, later, stationary and portable industrial versions of car and truck engines, either for belt use or built into engine-generators.