Initially built to Black Lightning specifications, the engine followed typical Vincent practice, with two air-cooled cylinders in a 50° V-formation and with the cylinders offset to improve cooling of the rear cylinder's exhaust valve. The engine displacement was , and it weighted , with a power output of @ 5000 rpm. The valves were operated by rockers and short pushrods driven by two camshafts mounted high in the engine's timing case, an arrangement euphemistically called "semi-overhead camshafts". The Picador motor was upgraded with a larger mainshaft, different big-ends, Scintilla magneto, and a double speed oil pump. To prevent fuel starvation during the U120D's rocket-assisted launch when accelerations of 10Gs would be generated, mechanical fuel injection driven from the propeller shaft replaced the usual carburettors. Unusually for an aircraft engine, the engine was mounted with the crankshaft transverse, although in the "Queen Bee" drone the engine was rotated 180° from its motorcycle applications, with the exhaust ports at the rear. An oilbath chain primary drive and a bevel gear drove the propeller with a 2:1 reduction from the engine speed.