Norton SOHC History - Part 1: 1926-1932

The Original CS1 Camshaft Engine
Norton’s first OHC engine was the CS1 (Camshaft Engine 1 – yes, I know, not very imaginative) and was designed by Walter Moore over the winter/spring of 1926-27. It was of a completely different design format to the engine that later became the Manx, but never the less used the bore and stroke dimensions of 79x100mm that had become synonymous with Norton 490cc single engines of the time. It was also the real start of Norton’s racing story so holds a very important place as being the first in a long lineage of camshaft single cylinder engines.
This first engine had a very distinctive timing case and bevel tube, giving it a very pretty ‘cricket bat’ look when viewed from the timing side. Although very successful at its first introduction (in the hands of Alec Bennett it won the 1927 Senior TT, with Stanley Woods, similarly mounted, setting fastest lap at 70.99mph before retiring), it was not actually very reliable, and many engine failures occurred alongside the successes. Stanley Woods later commented that he remembered when Walter Moore was designing the engine, he had both a Chater Lea and Velocette in his office, and thought he had probably taken the worst features from both bikes.

In 1930 Walter Moore had one disagreement too many with the Norton management of the time and decided to leave to go to NSU, where he had been offered a very good position. He there designed a very similar engine for them, which stayed in use for many years. A wit of the time commented that the initials might have stood for ‘Norton Spares Used’!

The new model was offered to the public late in 1930 (although still being advertised as the earlier CS1 and CJ model types) and also boasted a modified and updated chassis. Given that at this time the Wall Street Crash had really began to have an effect the world over and with many other motorcycle companies going to the wall, Norton’s good fortune in surviving must undoubtedly be owed partly to the success of this new model.

The earliest of the Carroll engines had a slightly different cylinder stud spacing to later engines, and did not have an oil pressure indicator or oil filter in the crankcase timing case. Also apparent in the earliest photos of the racing model in 1930 was an additional oil pipe running from the right side of the front cambox, down to the corresponding area of the timing case. I assume this was to assist oil drainage, although it was removed by the time the 1931 model range was introduced. This earliest of models also looked to have a top bevel inspection cover with a slightly different curve to later models.
Another interesting point with the early versions of the engine is that they were fitted with standard coil valve springs. This is surprising really, when one of the International and Manx engines most well known and refining features was its later use of exposed hairpin valve springs, with associated oil loss! Hairpin springs were not introduced until 1934.

Anyway, back to 1932. As well as the alloy bits and a larger fuel tank, another key change was the introduction of checksprings on the girder forks, which according to Stanley Woods made a big difference. Racing machines were fitted with a wider spring than their road going counterparts and were parallel, not tapered.
If there was a point where it could be argued that the road going version and the out and out racing bikes first started to go their separate ways, then in many respects it was at this time, and was the beginning of what later became the Manx racing version.

As an example of this (and one that even I had not noticed until a couple of years ago), the parallel springs employed on racing Norton’s were not the only difference on the front forks. Look closely on genuine racing Norton’s fitted with girders from this point forward and you will note that they were not fitted with a side damper on the lower spindle, as all other Norton’s were (including the International and CS1). I assume this was because the better handling associated with a parallel spring precluded the need for a damper and in most cases the racing machines were also fitted with a top mounted Andre damper. Although of marginal benefit, I expect the lack of this extra metal meant slightly less un-sprung weight as well (not sure if the benefits were understood at the time though!). If you look at the photographs of my own 1938 rigid racer on the homepage you will note it is fitted with these parallel springs and no side damper.