For example 8-T-33445 is a 1938 Speed Twin (later identified as “5T” instead of just “T”). Frame prefixes were ‘TL” for the 3T up to 1948 and TC for 1949. TR5 models had separate number series; engines from 101001 to 106424, frames from TC11001-T to TC13107-T.
Year shown in engine number prefix with two figures. This practice followed religiously and some single prefixes may appear on postwar models. TR5 models did not have separate number series but ran concurrently with all other models. Note: All Grand Prix T-1 00’s have letter ‘R” suffix following engine and frame numbers.
This three-letter TRIUMPH CODEYX code ran until, and including, 1923.(Apart from the Model LW/Junior/Baby which continued with it.) Thereafter further letters appeared in the stamping, which were not within the letters of the code.
The much respected late Bob Currie told me that no one had made sense of the new code, while another said that the letters didn't mean anything.
So I started collecting Triumph engine numbers and letters from surviving machines.