Compiled by Russell McIntyre of New Zealand
Engine Identification, on Russell's GEM
| U | CZ/ | D | 97468/ | B5 |
| (1) | (2) | (3) | (4) | (5) |
600cc Sport engine with Dry Sump Lubrication, 1954 model made between 1st Sept,1953 to 31st August, 1954, serial no.97468 with deviation B5.
1) The first letter before the oblique (/) mark identifies the cubic capacity of the cylinder, or of each cylinder if the engine is a twin.
(2) The remainder of the letters before the oblique mark identifies the engine type.
(3) The first letter after the oblique identifies the year of manufacture
(4) The serial no. of the engine follows immediately after the letter identifying the year of manufacturer.
(5) Additional letters after another oblique stamped immediately after the engine serial no. identify any deviations from standard specification. An (*) after the serial no. indicates the engine incorporates parts, which deviate from the standard specification.
Cylinder Capacity (First Letter)
| Letter... | Volume... | Valves... | Bore x Stroke (mm) |
| A | 300cc | Side Valves | 70x78 |
| B | 250cc | Side Valves | 64.5x79 |
| E | 375cc | Side Valves | 74x85 |
| F | 300cc | Side Valves | 70x76 |
| G | 350cc | Side Valves | 70x88 |
| I | 350cc | Side Valves | 70x90 |
| J | 500cc | Side Valves | 80x99 |
| K | 500cc | Side Valves | 85.7x85 |
| L | 550cc | Side Valves | 85.7x95 |
| M | 275cc | Side Valves | 70x97 |
| N | 200cc | Side Valves | 55x83 |
| P | 250cc | Side Valves | 62.5x80 |
| S | 350cc | Side Valves | 74x80 |
| U | 600cc | Side Valves | 85.7x104 |
| V | 175cc | Side Valves | 60x62 |
| Z | 175cc | Side Valves | 55x73 |
Note: The GEM 810cc Twin engine has two 405cc cylinders with a 3" Bore x 3-1/2" stroke and was made by Howard.
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Engine Type: The next group of letters are often used in combinations of twos or threes.
| Letter... | Type |
| T | Twin Cylinder |
| O | Overhead Values (cancels reference to side valves) |
| W | Water Cooled |
| Z | Dry Sump Lubrication |
| S | Short Stroke Sports Engine or Special |
| C | Sports Engine |
| R | Racing Engine |
| Y | Twin Exhaust Port Cylinder Head |
Year of Manufacture: Can help you date your Rotavator if original engine.
| Letter... | Year... | Letter... | Year... |
| P | 1920 | P | 1940 |
| N | 1921 | N | 1941 |
| E | 1922 | E | 1942 |
| U | 1923 | U | 1943 |
| M | 1924 | M | 1944 |
| A | 1925 | A | 1945 |
| T | 1926 | T | 1946 |
| I | 1927 | T | 1947 |
| C | 1928 | C | 1948 |
| S | 1929 | S | 1949 |
| W | 1930 | W | 1950 |
| H | 1931 | H | 1951 |
| Y | 1932 | Y | 1952 |
| Z | 1933 | Z | 1953 |
| D | 1934 | D | 1954 |
| R | 1935 | R | 1955 |
| V | 1936 | V | 1956 |
| F | 1937 | F | 1957 |
| O | 1938 | O | 1938 |
| G | 1939 | G | 1959 |
Note: Take into account the War Years during which machines for civilian use were no longer manufactured. It is worth noting that the J.A.P. production year ran from 1st September of the year previous to that identified by the dating letter, and ended on the 31st August of the year indicated.
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