And why is yours 1cc more than mine. 
I have a spare reprint manual in A4 size and parts list. Email me off site if you want pictures 
Ron
email (option): ronpier@talk21.com
The cc of a Big 4 is nearer 634 than it is 633 if you work it out. Bore 82mm x 120mm = 8.2cm x 12cm
Pi x (r x r) x length = volume so 3.142 x (4.1 x 4.1) = 52.81702 x 12 = 633.804cc
So really it's a 634cc Bike 
email (option): horror@blueyonder.co.uk
Well Norton called it 633cc! Maybe their maths was not as good as your Dave
Ron
email (option): ronpier@talk21.com
Daves using a calculator...at Norton they used the entire staff of the competition shop and still ran out of fingers.... ...Ian.. 3.142 x41 x41 x120 = 633.804cc
email (option): Ian@wright52.plus.com
On my first encounter with a Big 4 engine I wasn't sure what cc it was, thinking maybe 600 or 650, I knew there were 2 sizes of Big 4 engines but didn't know the exact sizes. It was easy enough to work it out from the bore and stroke stamped on the case. When I worked it out to be 634 I thought it was an odd size, then strange to see Norton had it listed as 633cc
Maybe Ian's right and they couldn't find someone in the workshop with 0.8 of a finger
email (option): horror@blueyonder.co.uk
BSA Gold Star..Winner of more individual events than any other motorcycle, in trials, motocross and road racing.. the Clubmans TT was axed due to the total domination of the Gold Star in both junior and senior classes..World Motocross Champions, International Trials Champions, TT sidecar and British Sidecar Champions, Daytona winners etc.etc...From 1929-1972 BSA won 60 British titles, 2 World titles and 1 European title, thousands of individual event wins and numerous team and manufacturers awards in Europe, America and the UK. They also dominated Motocross in America for 10 years and won the Maudes Trophy 3 times for good measure..... ...Ian
email (option): ian@wright52.plus.com
I must admit that I hadn't realised what Johnny-come-latelies BSA were on the motorcycle scene. I should've said 'first forty years' - I'm fully aware that the world became bored with watching Gold Stars ride round and round during the 1950s.....
Ah yes Rik, Norton were almost unheard of for racing in the 50's
email (option): horror@blueyonder.co.uk
Hmmm...'Johnny come lately'(not really) BSA was formed in 1861 to standardise the production of small arms..Nortons were formed in 1898, making bicycle chains and other fitments...BSA manufactured bicycles from 1880-87 when production ceased to re equip the British Army with new Lee Metford rifles at 1200 per week....Norton produced their first motorcycle in 1902 and with their own engine in 1908...in which year BSA recommenced complete bicycle manufacture.(rather than bicycle components) BSA produced thier first motorcycle in 1904 and with thier own engine in 1910..Norton were bankrupt by 1912. They were rescued by RT Shelley but were not considered big enough to obtain government contracts by the outbreak of WW1...BSA made 10,000 rifles a week (at peak), 145,000 Lewis guns, motorcycles, bicycles, shells, other munitions etc. etc.....Ian
email (option): ian@wright52.plus.com
Don't forget my 2 pounder anti tank gun in 1941 Ron
email (option): ronpier@talk21.com