1950 to 1962 Pre-Unit 500 & 650cc
Engine numbers had a prefix indicating the model type along the lines above such as 3T, 5T, 6T, T100, T110, 3TA, 5TA etc. This was followed by a number from the list below.
YEAR - Pre-Unit 500 & 650cc
1950 - From 100N
1951 - 101NA to 15808NA
1952 - 15809NA to 25000NA then 25000 to 32302
1953 - 32303 to 44134
1954 - 44135 to 56699
1955 - 56700 to 70929
1956 - 70930 to 82799 then 0100 to 0944
1957 - 0945 to 011115
1958 - 011116 to 020075
1959 - 020076 to 029363
1960 - 029364 to 030424 then D101 to D7726
1961 - D7727 to D15788
1962 - D15789 on