The first two-stroke petrol engine was invented by Dugald Clerk in 1878 and this model of the historic engine was displayed by A Atkinson at Harrogate in 2011. The model was machined from bar stock using a drawing that appeared in a book describing the Rolls Royce Crecy, a supercharged V-12 two-stroke engine, to illustrate where the two-stroke engine came from.

One of the original engines was installed in the University of Glasgow and was connected to a Siemens dynamo to power the lighting in Lord Kelvin’s house. Clerk’s engine is remarkably similar in principle to the modern large, low-speed marine diesels - highly efficient forced induction two-strokes.

No detailed information was available to help with the design of the model, and it was drawn up as a loose copy rather than exact replica, to compare it with the later crankcase induction two-stroke.

Spark ignition is used, although the original may have used a hot tube.

As there is no petrol/air mixture in the crankcase it was possible to use the crankcase vacuum to draw lubricating oil into the big end bearing by fitting a non-return valve.

The engine runs very evenly and smoothly, unlike a crankcase induction engine, and it does not four-stroke at low speed, although it does run out of power at ‘moderate’ revs as there is no overlap of the induction and exhaust timing as in other engine types.

The cylinder has a conical combustion chamber; it was hoped that the engine speed could be controlled like a diesel using the mixture rather than throttle opening, the theory being that the mixture could be weaker lower down on the cylinder and rich only near the point of ignition.