As did the majority of their contemporaries, Norton relied on the sidevalve engine until the introduction of its first overhead-valve design in 1922, the Model 18. This proved a very successful road machine.
Competition was a rather different story, as Velocette's OHC KTT had dominated the field in the 1926 Junior TT. Norton responded with a similar overhead camshaft engine the following year.
The Walter Moore engine proved an excellent design; it retained the Model 18's 79x100mm bore and stroke and employed bevel gears and a vertical shaft to drive the cams in similar fashion to the Velocette. The new machine sported a cradle frame and, for the first time, a saddle tank. At its debut it secured a win in the 1927 Isle of Man Senior TT with Alec Bennett at the helm, finishing a full 8 minutes in front of the second place machine. Stanley Woods, also on a CS1, established a new lap record of 70.99 mph.
The production version of the new CS1 (Camshaft Senior Model 1) duly appeared at the Motor Cycle Show later that same year and continued as Norton's top-of-the-range sports machine until the introduction of the International.
NSU enticed Walter Moore away from Norton, and there he developed a very similar machine for the German company. Norton responded with a new version of the CS1 designed by Arthur Carrol, and this engine became the basis for all of their future OHC and DOHC machines. It remained in production until the onset of war in 1939.
The CS1 is a landmark sports model and is regarded by collectors and enthusiasts as one of the most desirable Norton motorcycles.
Production Years: 1927-1939
Power: 18.3 KW
Displacement: 490 cc
Engine: OHC Single
Maximum speed: 85mph (1928), 190 km/h (late models)
Weight: 145 Kg
Sources: Motos Antigua HD, et al