Norton

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.

Installed in a Cooper Mk IX

and installed in the back of a Kieft

"Servicing the Manx" reprinted from Motor Cycling April 1957 - Click Here

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
Designed by Walter Moore
ES2 = Extra Cost, Sports Mk 2
Pushrod, OHV, long stroke (79x100mm, or 3.1x3.9”), 490cc, c.21bhp originally.

1927: Norton CS1 engine released:
CS1 = Camshaft Senior Model 1
Developed out of the ES2. The first Norton OHC engine
SOHC, long stroke (79x100mm), 490cc, c.25bhp
Unsuccessful at first, requiring redesigns over the next couple of years.

Both the ES2 and CS1 were used by poorer 500 builders.

1931: Norton International released
A complete redesign by Arthur Carroll
SOHC, long stroke (79x100mm), 490cc, c.29bhp
Also known as Model 30 in 500cc trim. Also shortened to Inter.
1931 for first works race versions.
1932 for customer road versions – available with a range of mods to give performance between road and full works race spec.
External hairpin valve springs available early, mainly for easy replacement on race engines.
1936: Optional alloy head and bronze-linered barrel released as options (not available when production recommenced in 1947, reintroduced in 1953)

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
At this stage, a single-cam development of the International, by Joe Craig.
First sighting of the iconic “big black head” and Norton cover plate.
Only available in works race spec. in 1937 and (in significantly redesigned version) 1938. Production halted for the War.
Re-introduced in 1947 as a road-race engine and bike (effectively an uprated Norton International)
SOHC, long stroke (79.62x100mm, or 3.135x3.9”), 499cc, c.47bhp
Fitted with a choice of Amal carburettors – initially RN-type until June 1952, then GP-type, with TT-type available as an option.

1949: Manx engine revised to DOHC – the classic “double-knocker”

Head redesigned to DOHC.
Retains the bottom end and cylinder dimensions of the SOHC Manx engine

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.
Manx engine crankcase is strengthened
Sometimes known as the Featherbed-type engine

August 1951: Featherbed-chassised Norton Manx becomes available for sale.
Engine gains sodium-filled exhaust valve

1953: Norton Motorcycles is bought out by Associated Motorcycles (AMC), already owners of the AJS and Matchless brands.

1953: Manx Short-stroke motor developed:
86.0x85.6mm (3.39x3.37”), 499cc
Short stroke increases rev limit from c.6,500 to 7,200rpm, increasing power to c.54bhp in race trim (N.B. In 1956, road engines were guaranteed as giving 47bhp @6,500rpm on petrol).
Apart from obvious changes to pistons, combustion chamber, head and cams, the entire engine is revised – in effect it is a completely different engine with few interchangeable parts.
Despite the greater peak power, this engine was generally not adopted by Formula III racers. Already close tolerances made it difficult to achieve the higher compression ratios for methanol, and the power band was much narrower.
Long-stroke production ceases on release of the Short-stroke model.

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:
Exhaust valve size reduced
Inlet valve & port redesigned
New cams fitted
Cooling improved
Timing adjustment revised
Lucas “Rotating magnet” magneto fitted as standard.

1957: Engine revised:
Inlet valve now sodium-cooled
“Flat-top” piston introduced (N.B. piston is still a pent-top design, the flat is relative to earlier versions and relates only to the top of the crown).
Con-rod strengthened and crank pin redesigned.
Bevel gears to head redesigned.

1963: Last Manx engines and motorcycles produced.