Does anyone have the original balance factor figure for Norton Big 4 flywheels? I have a set to get balanced and will probably apply the factor I generally use for BSA engines...but it would be nice to know the original figure....Ian

Lex is on his way to my house this evening. I'll ask him if he knows. Ron

email (option): ronpier@talk21.com

I was told when my 16H bottom end was having a birthday that the Norton singles in general were at 50% ex factory. Mine checked out at 48%.
I too will be interested in feedback from those who know.

Thanks Iain..BSA used a 58% balance factor..I have them balanced to 60%...Ian

Ian - have just checked back on a thread on the WDNorton forum and there is feedback there of successfully using a 62% factor on a 16H rebuild - allegedly better (smoother) for open road running. Bob who reported this was planning on doing something similar on his Big4 when he next had it apart.
So your BSA numbers may be the go?

Hi Iain, This figure (60%)works well for the BSA. The Big 4 I am told, vibrates like a good 'un to the extent it will shear off parts from the frame.
I plan to use the 60% factor for the flywheels I am currently working on but was interested to know the original figure for comparison. Balance factor affects each bike differently as the 'sympathetic' vibration frequency (when it all starts to shake at the same frequency as the engine) is dependent on a number of different factors such as the stiffness of the frame, triangulation of the engine within the frame, rigidity of the engine plates and crankcases etc. etc.
So, if you build a Triton for example, the vibration levels may be different when you fit the Triumph engine to the Norton frame...even with the same balance factor.
It's all guesswork when you alter the balance factor..the aim is to move the 'sympathetic' frequency point to an area of the rev range that is infrequently used..so for the Big 4 probably at the upper end. Altering gearing can also have an effect as it alters the most commonly used rev range. Maybe the Big 4 should be fitted with Norton Commando 'Isolastics'? ....Ian