Like the others the Minor had a robust steel five-bearing crankshaft, but unlike them the long studs bolting the cylinder heads to the crank housing were replaced by short studs and flanges at each end of the cylinder barrels.

Light alloy was used for the cylinder heads and con rods, while the valve gear was adopted with little change from the Hermes IV.

The Claudel-Hobson down-draught carburetter featured independent altitude control, and the dual-redundant magnetos were of B.T.H.

The Minor was known for excellent reliability, and had a major "win" when it was selected to power the RAF's Taylorcraft Auster observation aircraft.

Although externally identical, the Series II engine was redesigned to operate on 77 octane fuel, as opposed to the original's 70, increasing power to 100 hp (75 kW).