At the end of 1918, Brough announced they would be initially concentrating production on their 3.5 hp (489cc) flat-twin motorcycle. This was bench tested at 14 bhp at 4200rpm, and it would go to 5600rpm, which was quite high but was guaranteed by George Brough 'to the extent of £100'. The engine had detachable heads with the valve seats integral and the rockers 'enclosed in neat aluminium cases'. Light aluminium pistons, roller bearing crankshaft, and two ball bearing mounted camshafts, are further indications of development work during the war.