As well as giving a clean look to the engine, with the pushrod passages part of the cylinder block casting, unit construction reduced the number of places oil could leak from.

[3] A range of these 650 cc (40 cu in) Star twins were produced between 1962 and 1972, and improved on the old pre-unit A7 and A10 series, being lighter and easier to manufacture, with more up to date styling.

[5] Not enough time was spent on testing and development as BSA were struggling to remain competitive with Triumph models and the emerging Japanese motorcycles.

[7] In the US the 650 Star twins were selling well with styling changes including high rise handlebars and more streamlined fuel tanks.

This was sorted out by 1972 but by then BSA were facing serious financial problems and stopped production of the outdated 650 Star twin.