The Norton Manx "Double Knocker" became the engine to have in 500 racing. Official output was about 50 bhp, 10% more than the JAP but specialist tuners managed significantly greater figures. The downside was (and is) the much higher cost and limited availability. Steve Lancefield, Francis Beart and Ray Petty became the tuners of choice for the Norton.
The Manx was originally designed in 1927 by Norton’s Chief Designer, Walter Moore. A long stroke (79 X 100mm) overhead cam single, it was reliable and powerful enough to bring Norton success at the Isle of Man in that year. Joe Craig took over responsibility for the racing department and, in 1938, modified the valve gear operation to “double knocker” form. At first, Norton refused to sell engines alone so wealthier competitors purchased complete bikes and sold on the spares, inadvertently this helped create a complete new motorcycle, the Triton, when riders began mating the Norton Featherbed frame with a Triumph engine.
Through the years, a number of developments were introduced including a combined, forged, main shaft and flywheel, additional piston rings, and the introduction of an all aluminium head. The stroke was reduced several times during the fifties until Norton officially withdrew from racing in 1956.
Timeline for Norton engines used in Formula III Cars:
Note: All the model types below (ES2, CS1, International & Manx) were used for both engines and complete motorcycles, which can lead to confusion. Works Norton engines in any model year may have different bore & stroke from the customer version.
1927: Norton ES2 engine released
1927: Norton CS1 engine released:
Both the ES2 and CS1 were used by poorer 500 builders.
1931: Norton International released
We believe it was the International that was specified by Ron "Curly" Dryden and Spike Rhiando for their 1948 Cooper Mk IIs. These were the earliest serious competitors to opt for Norton over JAP (or Vincent).
1937: Norton Manx released
1949: Manx engine revised to DOHC – the classic “double-knocker”
Head redesigned to DOHC.
1950: Norton Featherbed frame developed by Rex McCandless.
Mated to the Manx engine, this creates the iconic Manx motorcycle shape with silver fat tank, drop handlebars, and short racer seat.
August 1951: Featherbed-chassised Norton Manx becomes available for sale.
1953: Norton Motorcycles is bought out by Associated Motorcycles (AMC), already owners of the AJS and Matchless brands.
1953: Manx Short-stroke motor developed:
1954: Norton stops running a works motorcycle racing team, but continues supplying engines and frames to privateers.
1954: Short-stroke Manx becomes available for sale.
1956: Engine revised:
1957: Engine revised:
1963: Last Manx engines and motorcycles produced.