I cannot find any engine number on my 3HW. On the standard place, at the left side of the engine under the cylinder, there is nothing. And also the framenumber in the upper ring of the ball head is missing. The only numbers I have found are TEC 942, Triumph Engineering Company September 1942, but that is the date the motorcycle was given to the army. The other number F1642, is in the neck of the ball head and is probably a partnumber of Triumph.