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How to determine age and manufacturer of a Long John bike (and other Danish bikes)

Most Long John owners would like to know age and manufacturer of their bike. On Danish bikes you´ve got a good chance to get this information by analyzing the serial number. In 1942 Denmark introduced a nationwide sytem of serial numbers for bicycles and mopeds which encodes both the manufacturer and the year of manufacture.

Where to find the serial number

On Long Johns the serial number can be most likely found in one of these locations:

1: on left side of the top tube (SCO, Monark)
2: on left side of the seat tube (older SCO and others)
3: on the steering tube (Monark)
4: upper side of chain stays, between bottom bracket and rear wheel (Esimex)

Other popular locations for serial numbers on bicycles are under the bottom bracket and on the rear drop-outs.

Maybe you won´t find a (valid) serial number for one of the following reasons:
-the bicycle was built before 1942 when serial numbers weren´t mandantory in Denmark
-the number (or parts of it) got lost due to abrasion, scratches, corrosion or any other damage
-the number (or parts of it) is covered with paint
-it´s not a Danish bike or it was not built for the Danish market

Serial number on the seat tube of a 1955 SCO Long John.

Decoding a serial number

  imp. manuf. seq. nr. yr
serial nr: W BK 12345678 B

imp.: Imported bikes (not made in Denmark) are marked with "W", otherwise this field is left blank.
manuf.: letter code indicating the manufacturer or importer (1-3 letters, see list below)
seq. nr.: sequential number assigned by the manufacturer (up to 8 digits)
yr: letter code indicating the year of manufacture (see list below)

Note: Serial numbers of Danish bikes built before 1942 don´t necessarily meet this specification. The same applies to Monark Long Johns produced for the non-Danish market.

Manufacturer codes

Every single manufacturer/importer has its own official and unique letter code(s). Since 1942 there have been several hundred manufacturer codes in use. Some of them are listed here:

AHarly Bech Sørensen, Silkeborg
AAAnton Nielsen A/S, Århus
AVA. Winther A/S, Them
BB, BKBørge Kildemoes Cykelfabrik A/S, Nr. Lyndelse (Danish importer of Monark Long Johns)
BPBohnstedt Petersen A/S, København
BTTaarnby A/S
CFCykelhandlernes Centralforening, Brabrand
CKJensen cykler (C K Jensen)
EEEgedesø, Odense / Everton, Nørre-Åby (bought by Smith & Co in 1995)
G Dansk Cykelværk Grand A/S, Nørre-Åby
HMHaderup Maskinfabrik, Haderup
LLSorte Jernhest
MBMBK cykler
NNordisk Cykelfabrik A/S, København
OCOtto's Cykler, Dragør
PSSchrøder cykler
R, ARVilh. Nellemann A/S, Risskov
S, SSSCO (Smith & Co), Odense
SXSaxil cykler
URUrania cykler
VELVelorbis, København (Danish distributor of Monark Long Johns since 2007)
VGGrebart cykler
XXEsimex, Hanstholm

(Caution: this list might possibly contain flaws)

Year codes

The last digit of each serial number is a letter matching the year of manufacture. Since there are less letters than years all letters are re-used in cyclic intervals. See list:

A1942 1964 1985 2006 J1950 1972 1993 S1958 1979 2000
B 1943 1965 1986 2007 K 1951 1973 1994 T 1959 1980 2001
C 1944 1966 1987 2008 L 1952 1974 1995 U 1960 1981 2002
D 1945 1967 1988 M 1953 1975 1996 V 1961 1982 2003
E 1946 1968 1989 N 1954 1976 1997 X 1962 1983 2004
F 1947 1969 1990 P 1955 1977 1998 Z 1963 1984 2005
G 1948 1970 1991 Q 1956
H 1949 1971 1992 R 1957 1978 1999

The letter Q was only used once (in 1956). The letters "O", "I", "W" and "Y" have been completely dropped, mainly to avoid confusion with similar letters and numbers.

As you see from the table, a single letter code can match up to four different years. For a correct assigment of your year code you´ll need at least a rough idea in which decade your Long John was built. The Long John frame guide might help you to identify the production period of your frame.

Additional links regarding this subject:

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