Your story about the D’Yrsan three-wheeler (Motor Sport, March 1987) included a side view of the chassis complete with the Ruby engine, said to be a side-valve design.
To my mind, it is of the ohv variety, complete with rockerbox cover and side sparking plugs. The plugs are the give away.
You will remember the Morris “Ten” of the late 1930s had side valves, but a fake rocker cover above the top sparking plugs may have fooled the public at the time, as it did me.
J Aherne, Edinburgh
Yes, we take the point and think we, too, were fooled when writing the caption. WB