Vivian Lewis Limited sold a large number of engines for industrial and agricultural applications: pumping water, sawing wood, cutting chaff, cleaning wheat, turning the separator, and a dozen other jobs... It is not known whether these petrol engines were made in house or sourced externally. Lewis were certainly capable of manufacturing engines, however the practices on the motorcycle side of the Lewis business suggest that they were most likely bought in and rebadged as "Lewis".
The exact dates of manufacture are not known, but Lewis agricultural engines were first exhibited at the Royal Agricultural and Horticultural Society's Autumn Show in March 1908. Numerous advertisements for the engines appeared in the press and in Lewis advertising literature. The Vivian Lewis letterhead from 1917 still listed agricultural petrol engines amongst its offerings, but the 1921 letterhead does not mention engines. Additional information would be most welcome.
There are few surviving Lewis agricultural engines, but here is one snapped at a rally about 30 years ago: