Norton Big 4

[acid_drop]

Can anyone tell me why the Norton big 4 was so called,
when it was a single.

[L.A.B.]

Can anyone tell me why the Norton big 4 was so called,
when it was a single.

Because it was "Four Horsepower".

And engines of that period would commonly be referred to by their horsepower rating. The old horsepower ratings should not be confused with "Brake Horsepower" (BHP)as is used today.  

[Bruce]

Yes that is correct it was an old taxation class which related to something to do with the bore or stroke of the engine and in this case it was just under 4 hp hence .I have owned and used one for many years.
 

[acid_drop]

Thank for the reply's chaps. This will finish a discussion at my bike club. Much Appreciated.

[L.A.B.]

Yes that is correct it was an old taxation class which related to something to do with the bore or stroke of the engine and in this case it was just under 4 hp hence .

The original 1910 Big 4 had bore & stroke dimensions of 82 x 120mm, (633cc) and the RAC horsepower formula is:

http://www.designchambers.com/wolfhound/wolfhoundRACHP.htm

     " h.p. = (D2 x n)/2.5

 where D = the diameter of the cylinder in inches [1" = 25.4mm], and n = the number of cylinders"




Which I calculate to be = 4.147 Hp.



From 1948 the capacity of the Big 4 was reduced to 597cc, as the stroke was shortened to a mere 113mm.