Between 1907 and 1910, Lewis produced a range of motorcycles powered by 3 h.p. motors in both air-cooled and water-cooled forms. The earliest sighting of the water-cooled model is in a photograph in the local paper The Critic in October 1907, while the air-cooled model was described as "a distinct novelty" in a report of the Autumn Show in March 1908. Based on engine numbers from survivors, perhaps 500 machines of this type were produced.
There seems little doubt that, at least in air-cooled form, these motors came directly from the Stevens Motor Manufacturing Co., Ltd. of Wolverhampton. Before beginning construction of their own machines (bearing the famous AJS brand) Stevens supplied motors to the motor trade, particularly to Wearwell. Their range of offerings was extensive - perhaps too extensive with receivers called in in 1907 to guide the company through some difficult times.
This advertisement appeared in The Motor Cycle, 21st July 1909:
Notice the name-plate under the timing chest, shown blank in the illustration but obviously designed to bear the customer's name on request. Lewis seem to have availed themselves of this feature, with Lewis-Stevens engines bearing the Lewis name on this riveted-on plate.
The Stevens motors varied little over the years that they were used by Lewis, the most obvious change being the switch from bronze to alloy timing covers around 1909. Perhaps the alloy-cover motor is the "latest model" referred to in the advertisement. One surviving Lewis-Stevens motor has a steel timing cover.
It seems likely that the water-cooled 3 h.p. motor of the period (like that in my 1909 Lewis) was also sourced directly from Stevens, although we have no confirmation of this yet. An unresolved question is why the water-cooled cylinders on the last of the Stevens engines are so similar to those on the first of the Precision engines that replaced them. My current thought is that Stevens may have sourced their cylinders externally, and when Precision began manufacturing water-cooled motors, they bought in their cylinders from this same source.