After the After the WW I, Calthorpe was able to produce their own Calthorpe 350cc engines which was released in 1925. Calthorpe also produced models with a 500ccm engine of their own design, but due to high prices and bad design only 100 models with the 500 cc engine were ever produced and sold.
Calthorpe 350 review
Initially using JAP and Precision engines, after the First World War they also used Peco, Villiers and Blackburne units. By 1924 they were producing their own 350cc ohv engine. The Ivory series Calthorpe 350 motorcycle began in 1928 and was very well received with its saddle tank and duplex frame, but by the late thirties the company was in decline and went bankrupt in 1938. Another revival attempt in 1945 using Villiers two-stroke powerplants was also unsuccessful. More specs and user manual of Calthorpe 350 you can see in next overview.