Norton International
In the 1930s, Norton developed the overhead camshaft engine to a level at which it became a world beater on road and track, laying the foundations for the most famous race bike ever made
There was nothing new about overhead camshaft engines when Norton made their first ‘cammy’ in 1927, but sometimes good ideas come too early for the technology of the day. Velocette produced their successful ohc 350cc model in 1925, but several other manufacturers tried to follow without success, mainly because few understood the timing requirements to capitalise on the more direct valve operation.
The principle is simple enough. By moving the camshaft from the crankcase to the cylinder head, you dispense with flex-prone pushrods that cause loss of valve lift and add undesirable reciprocating weight. Norton were among those who persevered, using two different designs from two different designers. The first engine, penned by Walter Moore, was ready for the 1927 TT; it used bevel-gear shaft drive to the single overhead camshaft, the shaft tube emerging from an upended oblong casing, giving rise to the nickname ‘the cricket bat’. After setting a 70mph lap in practice, a ‘cricket bat’ Norton won the Senior TT for Alec Bennett. The new model reached the public in 1928 as the CS1 (Cam Shaft 1), joined by a 350cc CJ (Camshaft Junior). But neither model was able to reprise the success of 1927. All the CJS retired in the Junior race and the best the 500s could manage was fifth and sixth place. Despite the appointment as development manager of former TT racer Joe Craig, a man whose name became synonymous with advancing the cause of Norton’s cammy racers, 1929 and ’30 proved little better with numerous retirements and mediocre placings. Yet, uncertain though it was, 1930 was the dawn of a new era. Walter Moore left the company to join NSU – who soon had a ‘cricket bat’ engine of their own – and his replacement, Arthur Carroll, completely redesigned the ohc motor with the accent on simplicity. The combination of
Carroll’s design and Joe Craig’s engineering flair and determination would prove the perfect recipe for success, although in 1930 the four-valve four-speed Rudges still dominated racing and the three-speed Norton fared no better than fourth against a 1-2-3 Rudge Senior TT victory.
The tide changed in 1931, when Nortons took first, second and third in the Senior (along with setting a new 80mph lap record) and first and second in the Junior – it might have been another 1-2-3, but retiring with what he supposed to be ignition failure, Jimmy Simpson had settled down to watch the race before he thought to check his carburettor. Main jet cleared, he rejoined the race to come in eighth.
The Carroll Norton was called the ‘International’ Model 30 (500cc) or Model 40 (350cc) – or ‘Racing International’ for the racers. The term ‘Manx Norton’ wasn’t coined until after World War II. For the rest of the 1930s, Nortons dominated racing results around the world – but Arthur Carroll remains something of an unsung hero. Although he died in an accident in 1935, his winning race engine remained as he designed it until 1937. In that year, already trying to fend off multi-cylinder racers from Europe, Joe Craig adjusted the bore and stroke, upgraded to double overhead cams and strengthened the bottom end, coaxing the 500cc race engine to deliver 52bhp. But the basic DNA of Carroll’s engine is still to be seen in the late Manx engines, while the road Internationals retained the original profile until they were discontinued in the late 1950s.
Under Joe Craig’s influence, the company’s obsessive racing programme feasted on company profits, leaving little to improve the rickety Bracebridge Street factory’s finances. At the end of 1938, a shock announcement was made that the company would cease racing throughout 1939 to catch up on customer orders – although this was in part due to military contracts, with the political situation in Europe rapidly reaching crisis point.
But costly though they were, racing laurels did make Nortons – and the International in particular – very popular with fast road riders of the 1930s, creating brand loyalties that would be passed from fathers to their sons, ensuring a future generation grew up to respect the Norton name.
Some would argue that Velocette played an equal part in promoting overhead cam engines in the 1930s – certainly they beat Norton to the draw in both single and double ohc types – but the Velocette engine was always more delicate and the company concentrated on their 350cc, never making a 500cc version for the road. Norton kept their ohc racing engine winning for far more years than seemed possible, while ably adapting the technology to create a highly successful road bike; they may not have been first, but Norton made the ‘cammy’ engine their own.