Mike continued, "In the 1930s, H-D got into the V Series...the VL, the VLD, the VLH...up until 1936. Then they went (and stepped back a letter of the alphabet) to the U Series, which was a flathead 80-inch motor with a recirculating oil-pump system. Then of course they had the E Series, the EL, and the FL in the Knucklehead, right up into the Panhead. Although it was a completely different motor, the only thing that changed was the reference to the head design, still an E or F Series, one a Knucklehead, one a Panhead. That existed until right into the advent of the Shovelhead, still with the F designation."
If that isn't exactly as clear as 50-weight oil, here's a bit of information that could give us a handle on how it all came to pass. Let's call it "The SOS Connection." Back in the very early days of motorcycling, you ordered your parts via the manufacturer's catalog. And you did so via the prevalent means of communication at the time...not by the telephone, but rather by telegraph-i.e., dot, dash, dot. In fact, the motorcycle catalogs listed the parts in alphabetical telegraph code.
We delved into this interesting trail of evidence by placing the question before Buzz Walneck, National Motorcycle Hall of Fame member, who came up with an original Harley-Davidson factory order form from which he read several examples regarding the telegraph codes: "In 1914 if you wanted a single-cylinder, belt drive, you ordered an 'Acorn.' If you wanted a Model B with the chain drive, you ordered a 'King.' In 1916, if you wanted a three-speed Twin, you ordered an 'Egg.' And if you wanted the large seat, you ordered the 'Acorn Elephant.' If you wanted a '24 JD with standard 74-inch motor, cast-iron pistons, and electric equipment, you ordered a 'Roach.' And if you needed a '24 roller bearing for the center rod, the order code was 'Outhouse.'"
Aha-this could be the smoking gun, the connection between the telegraph, ordering parts, and the fairly weird number and letter designations. The telegraph molded the message. If you get a hold of antique catalogs you can see it for yourself.
One of the first, beyond-early unnamed motorcycles was "The Silent Gray Fellow," the name acquired by the bike's gray paint job and reputation for quiet running. Fair enough. "Sport Twin" and "61" were no-brainers, obvious references to engine configuration and engine displacement, respectively. And at this point we first hear the name "Knucklehead," which appears to have been a popular street name prompted by the resemblance to a fist of the new engine's rocker covers. This manner of parlance would carry over to the Panhead ('48-'65), Shovelhead ('66-'85), and even the Blockhead (Evolution '84-'00) as the engines evolved. After the 1999 intro of the Twin-Cam 88, the nickname "Twinkie" appeared in SoCal. We also heard somewhere (maybe over too many beers) that the V-Rod's engine was nicknamed the "Waterhead."
The various "Glides" circa '40s-'70s were factory names. The "Hydra" referred to the new telescopic-fork frontend that debuted in 1949. The "Duo" was so named for its swingarm rear suspension and twin shocks. The Electra-Glide (1965) was a Duo-Glide but now with electric start and a 12-volt system to go with it. The FX Super-Glide (1971) was a semi-blending of a non-electric-start FLH 74 engine, frame, and running gear with the frontend from a Sportster plus Willie G's "boat-tail" rear end. It's also considered the first factory production "custom."
A quick scan of the first Harley-Davidson bikes tells us the factory used the designations 0, 1, 2, 3, 4, 5/A/B/C, 5D...after which you can follow the alphabet over the next hundred years to literally span the letters A through Z. What was the Z Harley, you ask? Why, the '73-'75 Z90, a 90cc two-stroke wonder. But still the question remains unanswered. Was it just the luck of the draw? Did the FLSTCI (Heritage Softail Classic Twin-Cam 88) simply begin life back in 1918 as the F Model, so designated for its F-head design, and then accrue additional letters as the bike evolved to include FL, FLH, FLHT, and so forth? The "FL" in FLSTCI hearkens back to the F models, while "STC" translates to Softail Classic. So it seems the name game is an alphabet soup. At least in part.