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Motorcycle Discussions => British Bikes => Topic started by: acid_drop on July 04, 2008, 03:58:18 AM

Title: Norton Big 4
Post by: acid_drop on July 04, 2008, 03:58:18 AM

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

Title: Re: Norton Big 4
Post by: L.A.B. on July 04, 2008, 04:04:00 AM

Quote

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.  

Title: Re: Norton Big 4
Post by: Bruce on July 04, 2008, 07:07:28 AM

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.
 (http://i144.photobucket.com/albums/r183/brucebig4/big4.jpg)

Title: Re: Norton Big 4
Post by: acid_drop on July 05, 2008, 03:03:39 AM

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

Title: Re: Norton Big 4
Post by: L.A.B. on July 05, 2008, 04:03:18 AM

Quote

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.