You won't find many aircraft engines that require the owner to remove the valve covers and change the oil in each that splash lubricates the valve gear. While you're in there doing that every 25 hrs on the Gipsy, you adjust the valve lash. It's an engine utilizing early 1920s technology that was superseded in most other practical applications by the mid 1930s. It was used in 1946 because the Canadian designers were forbidden by their UK customer from using anything better.
It's interesting to conjecture why Dehavilland or others didn't try seriously to develop a modern light aircraft engine themselves, instead of giving up. I've seen it suggested that the post-war Blackburn Bombardier would have been a good replacement for the Gipsy, especially given how underpowered the Chipmunk ended up being, but others would know better than me whether the Blackburn engine was any less of a archaic antique than the Gipsy by the 1950s.
Another possibility would have been been to 'borrow' a German design for use in postwar British aircraft, as per BSA Bantam (DKW) motorcycle engine and Bristol (BMW) car engines.
Last edited by Silvaire1; 23rd Apr 2016 at 14:46.