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.

Sharing common engine and cycle parts with the larger BSA A65 Star 650 twin, it was an over-engineered machine and proved very robust.

The only major fault with the engine design was a plain crankshaft bearing on the timing side which, when worn, would cause a drop in oil pressure.

The A50CC Cyclone Competition built for the US market model year 1964 had dual 1 1/16" carburettors, higher 10.5:1 engine compression, magneto ignition, larger front brake, 2 gallon fuel tank and upswept open exhaust.

The A50C Cyclone Road built for the US market model years 1964 and 1965 had 1 1/16" dual carburettors, higher 9:1 compression engine and larger front brake.