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Spark Plugs for Nortons

The codes used by the various manufacturers give some information about the plug types. The first digit represents the thread size, followed by a number which reflects the heat range of the plug. The Champion and NGK plugs match well in this respect, but do not necessarily match well with others. This is because some have wider heat ranges and one plug may cover two from another manufacturer. As a rule of thumb, for NGK and Denso, a higher number means a colder plug whereas for Champion, a higher number means a hotter plug. The next letter describes the reach of the plug, except in the case of Champion where the first letter describes not only the thread but also the reach. Any other letters cover special features or materials used or if the plug is for competition use. A 'P' in the NGK range, a 'Y' in the Champion, or a 'D' in the Bosch range means that the plug is a projected electrode type.

MODEL NGK BOSCH CHAMPION ND DENSO  NOTES
 Big 4  B6ES  W7C  N5  W20ES-U  
 16H  B6ES  W7C  N5  W20ES-U  
 Model 19  B6ES  W7C  N5  W20ES-U  
 Model 30 / 40M  B10ES      W31ES-U  
 Model 30 / 40M  B10ES  W2CS  N57G/N82G  W31ES-ZU  Gold or platinum tip
 Model 50  B7ES  W5CC  N4  W22ES-U  
 ES2  B7HCS  W240T1  L5  W22FS-U  Short reach ½"
 ES2  B7ES  W5CC  N4  W22ES-U  
 Model 7  B6HS  W7A  L85  W20FS-U  Short reach ½"
 Model 77  B6ES  W7C  N5  W20ES-U  
 88  B6HS  W7A  L85  W20FS-U  Short reach ½"
 88  B6ES  W7C  N5  W20ES-U  
 88SS  B7ES  W5CC  N4  W22ES-U  
 99  B6ES  W7C  N5  W20ES-U  
 99SS  B7ES  W5CC  N4  W22ES-U  
 Jubilee  B7ES  W5CC  N4  W22ES-U  
 Navigator  B7ES  W5CC  N4  W22ES-U  
 Electra  B7ES  W5CC  N4  W22ES-U  
 G15  BP7ES  W5D  N4  W22EP-U  
 G15CSR  BP7ES  W5D  N4  W22EP-U  
 N15CS  BP7ES  W5D  N4  W22EP-U  
 P11  BP8ES    N6Y  W24EP-U  
 650SS  B7ES  W5CC  N4  W22ES-U  
 Atlas  BP8ES  W5D  N6Y  W22EP-U  
 Mercury  B7ES  W5CC  N4  W22ES-U  
 Commando  B7ES  W5D  N7Y  W22EP-U  Combat / some 850s
 Commando  B6ES  W7D  N9Y  W20EP-U  Most 750s / 850s
 Interpol 2  R0045G10 †    UG80PV    NGK C8E alternative ‡
 Classic  R0045G10 †    UG80PV    NGK C8E alternative ‡
 Commander  C8E *    G63    
 F1  C8E    G63    

 

 *

 Water cooled rotary Nortons run relatively cool, if you have oiling up problems, use C7E

 †

 This NGK racing plug is the correct heat range but is about 3 threads shorter.
 Going back to a longer plug later might be difficult due to carbon deposition

 ‡

The engine temperature of an air cooled rotary Norton varies greatly according to load.
 This can lead to oiling up problems on either the Champions or the racing NGKs.
 Many owners are now using C8Es this cures the oiling up problem but the plug is shorter.
 This might lead to problems if you then fit longer Champions and hit a deposit of hard carbon

Rotary plug information provided by Graham Wilshaw graham@startright.demon.co.uk

 

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