Typical engine numbers were for example:
8-T-xxxxx (Speed-Twin from 1938)
47-5T-xxxxx (Speed-Twin from 1947)
48-3T-xxxxx (350-ccm-Twin from 1948)
9-T100-xxxxx (Tiger 100 from 1939)
The engine numbers formed from the year of manufacture and the designation of the type. In period of 1937 to 1939 the last number of the year was used (7, 8 or 9) . From 1946 to 1949 the last two numbers (46 , 47...) and the type-designation.
Type-designations (for example):
T or 5T Speed Twin
T100 Tiger 100
3T 350er
TR5 Trophy
The engine numbers began from 1946 to 1949:
Year
1946 72000
1947 79046
1948 88782
1949 100762
1950 to 1962
Pre-Unit with 500/650 ccm
Engine number with placed in front type-designation (5T,6T,T100,T110 ect.)
Year
1950 starting from 100N
1951 101NA-15808NA
1952 15809NA-25000NA thereafter 25000-32302
1953 32303-44134
1954 44135-56699
1955 56700-70929
1956 70930-82799 thereafter 0100-0944
1957 0945-011115
1958 011116-020075
1959 020076-029363
1960 029364-030424 thereafter D101-D7726
1961 D7727-D15788
1962 D15789 --------