JAP
Engine Numbers
What age is your Iron Horse?
A question we get asked a lot and have struggled to find a definitive
answer to. The following guide will help give you at least a year of
manufacture.
To attempt an illustration we have used an actual Iron Horse engine
number...
and here's what those numbers mean...
Deciphering your Horse engine number centres
on the second digit. This is your year of manufacture and the letters
run in twenty year cycles, remembering that JAP years actually start
in the September of the previous year. In the example above the year
is 1948 but theoretically it could have been made in September 1947
but not after September 1948.
The first digit is the model number, in this case the Horse used the
Mk 5 engine and is so denoted here. Then comes the year, then the engine
number (which we have no details of, it is just a factory record), and
lastly the modifications. These are what the factory called deviations
from the standard specifications and could denote cam spec, piston type
etc. We have the codes for motorbikes but unfortunately the Horse engines
were designated as industrial motors and the codes we have don't apply.
|
Code
|
Year
of Manufacture
|
|
|
P
|
1920
|
1940
|
|
N
|
1921
|
1941
|
|
E
|
1922
|
1942
|
|
U
|
1923
|
1943
|
|
M
|
1924
|
1944
|
|
A
|
1925
|
1945
|
|
T
|
1926
|
1946
|
|
I
|
1927
|
1947
|
|
C
|
1928
|
1948
|
|
S
|
1929
|
1949
|
|
W
|
1930
|
1950
|
|
H
|
1931
|
1951
|
|
Y
|
1932
|
1952
|
|
Z
|
1933
|
1953
|
|
D
|
1934
|
1954
|
|
R
|
1935
|
1955
|
|
V
|
1936
|
1956
|
|
F
|
1937
|
1957
|
|
O
|
1938
|
1958
|
|
G
|
1939
|
1959
|