The roots of the Harley-Davidson S-125 go all the way back to World War II.
1948 Harley-Davidson Model S-125
Engine: 125cc air-cooled 2-stroke piston port single, 6.6:1 compression ratio, 52mm x 58mm bore and stroke, 3hp
Top speed: 45mph
Carburetion: Single Langsenkamp-Linkert
Transmission: 3-speed, chain final drive
Electrics: 6v, magneto ignition
Frame: Single downtube steel cradle frame
Suspension: Girder fork front, rigid rear
Brakes: 5in SLS drum front and rear
Tires: 3.25 x 19in front and rear
Weight (dry): 170lb
Fuel capacity/MPG: 1.75gal (6.6ltr)/90mpg (claimed)
Price then/now: $283/$3,000-$9,000
Who would have thought that a Harley-Davidson model would have its origins in Nazi Germany? That’s the case of the small-bore Model S-125, launched in 1948 following Germany’s defeat in World War II.
To the victor go the spoils, and since the Allied Forces (led by the United States, Great Britain and the Soviet Union) were victorious in World War II, they helped themselves, in the form of war reparations, to some of the loser’s goods. Among the booty, the Allies gained access to intellectual property belonging to Nazi Germany for such things as the V1 rocket (space travel, here we come), submarine and jet-propulsion technology — and motorcycles. Wait, motorcycles? Well, yes, and in this case the reparations included plans for a small bike powered by a 125cc single-cylinder 2-stroke engine originally developed in 1919 by Danish engineer Jorgen Akafte Rasmussen living in Saxony, Germany. Rasmussen called his small yet efficient piston-port induction 2-stroke engine Das Kliene Wunder, which roughly translates to “The Little Marvel.” In later years, people in Nazi Germany knew the bike that it powered as the DKW RT-125, and at war’s end plans for the little motorcycle were judiciously passed along to the U.S., Great Britain and Soviet Union to do with as they pleased.
Britain gave BSA (British Small Arms) the nod to build what became known as the Bantam, and the good folks running the Kremlin turned their DKW blueprints over to Soviet industrialists to build what became the Minsk M1A. Later, with the rise of the Soviet-backed Eastern Bloc of nations, Poland’s engineers were made privy to the DKW’s blueprints, leading to creation of the SHL M03 for adventurous comrades to ride. And, in a weird twist of fate, the little DKW even helped Yamaha of Japan enter the motorcycle market in 1955 with its YA-1. All this sharing makes you wonder: Had obscure countries like Iceland or Andorra expressed interest in supporting their own motorcycle industries, might they too have gained access to the DKW for their prototypes?
In any case, as a reward for its role in supplying the Allied armed forces with more WLAs than Hitler and his gang could blow up, Harley-Davidson was awarded its own set of DKW blueprints. That was of particular importance for Harley because the Milwaukee-based company was in want of an affordable, low-maintenance model to attract entry-level riders (read: beginners, consisting mainly of young people) to dealerships. Thus was born the Model S-125 (although, depending on the source, the bike was also called the M-125, or simply the Model S or Model M).
Moreover, the bike was rather successful in terms of overall sales, its 10,000 units sold in 1948 accounting for about one-third of all Harleys sold that year. But in his book Harley-Davidson: The American Motorcycle, author Allen Girdler suggests the Model S isn’t a success story. Rather, it’s “More like a fable complete with moral, which is that having a good idea isn’t always enough.” Simply, small bikes generally equate to small profits for the mother company. The big bucks then, as now, rested with the Big Twin models.
Even so, the S-125 proved to be efficient and reliable enough for Harley to keep it, and later variations based on the original, in the lineup through 1966. That’s when Italian-made 2-stroke tiddlers such as the M-50 and Rapido replaced the German-based single in the model line during the Swinging Sixties.
As 2-stroke designs go, Harley’s original DKW-based 125cc engine was based on the piston-port concept. A tiny carburetor fed pre-mix oil and gasoline that was stored in the peanut-shaped 1.75-gallon gas tank to a single intake port before the air/fuel mixture found its way into the crankcase as the piston began its upswing towards top dead center. The mixture patiently stirred around within the crankcase until pressure created by the piston’s downward thrust pushed the fresh charge up through the transfer ports and into the combustion chamber where ignition took place. As the piston returned on its down stroke the exhaust port became exposed so that the excess gases could exit, allowing the whole process to continue through another cycle by the crankshaft’s rotation. Bore and stroke measured 52mm x 58mm, displacing 125cc (7.6 cubic inches). Harley rated compression ratio at 6.6:1, and the sum total created a claimed 3 horsepower. Most sources quote Harley’s original acknowledged top speed for the S-125 at about 50-55mph, which is probably closer to being optimistic than accurate because Jim Davis, owner of our featured 1948 model, reports seeing 45 on his bike’s speedometer dial. “And it’s pretty accurate because I compared it to my Honda, which is almost spot-on,” he says.
Speaking of accuracy, by now some S-125 followers are wondering why the name Hummer hasn’t entered into the dialogue yet. After all, those Model S followers claim, the name for this bike is the Hummer. Not quite so: The Hummer moniker made its presence in 1955, and that bike was also known as the Model B, which itself was a down-sized version of the ST, which had an engine displacing 165cc based on an upscale variation of the original 125cc engine. Confusing? Not really, and to sort it out let’s walk through the little Harley’s evolution, starting in 1948.
As noted, Harley originally made about 10,000 of the little bikes, and they all sported rigid frames with girder-style forks that relied on what experts term rubber bands in the linkage to dampen movement. Recalling his first ride ever on a motorcycle, motojournalist Clement Salvadori recently wrote in Rider magazine about his experience with that rubber-band suspension: “The first bike I rode was a 1948 Harley 125, with a rubber-band suspension on the girder fork. Simplicity! I still admire the very, very basic design and the dependability,” he wrote in the August 2016 issue. Further smoothing out the ride was a pair of long coil springs supporting the rear portion of the classic solo seat.
The 170-pound bike rolled on 3.25 x 19-inch tires. A pair of dubiously effective, small-diameter, mechanically operated drum brakes brought the bike to a slow, yet ultimate stop.
The engine itself relied on a small left-side kickstart lever to get the show on the road. The low-compression engine didn’t require much of a kick, either, making the bike even more attractive to first-time riders. The 3-speed transmission relied on the usual 1-down 2-up shift pattern, with the shift lever on the left side.
Subsequent years saw incremental improvements to the S-125. The first major update was in 1951 when the clunky girder fork was replaced with an inverted telescopic fork. Harley termed this the Tele-Glide Fork, and one advertisement touted it as “A new riding sensation! Smooth-acting, Tele-Glide spring fork absorbs shocks, makes country roads seem like boulevards!” Those same ads promised more speed, too: “New motor power for quicker get-away,” stated the upbeat copy.
The larger engine — displacing 165cc — came in 1953, and with it more horsepower and a new name. Riders now had 5.5 horsepower to play with, and the bike was called the ST. The power must have proven to be too much for some states’ motor vehicle laws, though, because the following year Harley included another model, the STU, that had a restrictor plate within the intake tract to limit horsepower to under 5.
Harley’s quest to gain new riders heated up even more in 1955 — the year of the Hummer, which officially was the Model B, joining the ST and STU. This basic of basic designs prompted more sales among first-time buyers, and it wasn’t until 1961 that Harley injected new life into the small-bore engine to produce the Super-10, based on the ST’s 165cc engine. Clearly this model was intended for youthful high-performance-minded riders, as one ad stated: “Keen wheeling for teen wheeling.”
By 1963 the little tiddler had morphed into three models, the BTH Scat, BTF Ranger and BTU, all powered by the 175cc version of the original RT-125-based engine. The 1963 models included a new under-frame rear suspension design, putting it about 20-some years ahead of today’s classic Softail concept. But soon even these upgrades weren’t enough to keep the little air-cooled single-cylinder engine in the lineup and it was retired at the end of 1966. By that time Harley had produced about 67,000 bikes based on the original S-125 platform. Its demise helped mark the end of an era for Harley-Davidson.
For Jim Davis the story of Harley’s S-125 didn’t heat up until just a few years ago when he spotted a rusting motorcycle frame in his father-in-law’s shed. Curious, he pulled it out to learn more. “It’s my brother’s old Indian,” his wife told him. Jim wanted to know specifically what model it was, so he snooped around until he found part numbers on one of the rusted wheel rims. “I eventually determined the bike was a Harley 125,” he says. The more he learned about the little Harley, the more enamored he became with its style and design, prompting him to seek a 1948 S-125 that he could restore. One popped up on eBay, and he ventured from his home in Temecula, California, to Sacramento, California, where he ended up purchasing the tired-looking bike.
Unfortunately, the owner wasn’t entirely truthful about what he sold Jim, who through further research learned that only the frame and fork were of 1948 vintage. Even the engine was wrong — it was a 165. His quest continued for a 125cc engine. “I went through three different engines before I ended up with what’s in the bike now,” Jim says. That included a 125 based on a hodgepodge of various years, followed by a 1949-vintage engine before a call to Hummer aficionado Charles “Mutt” Hallam in Wills Point, Texas, resulted in a worthy set of 1948 engine cases. Mutt helped Jim restore the engine to 1948 pedigree, and that’s what’s in the bike now.
Jim’s learning curve about the Model S-125 accelerated again when he connected with Duane Taylor (Taylor’s Classic Motorcycles) in Salem, Oregon. Duane helped steer Jim to many of the right components, and his business was the source for some of the reproduction parts now on the bike.
Patience, persistence and perseverance are key virtues when restoring any motorcycle and Jim has those assets in spades. He hit the mother lode of parts one day while browsing Craigslist in search of a rear fender. A local buyer was selling a small cache of “Hummer” parts, and when Jim spotted a complete rear fender among the mix, he hustled over to the seller’s house with cash in hand. After a little negotiating, Jim drove home with a new rear fender plus a few frames, tanks, engines and more, most of which he flipped on eBay. Net result: a free fender and a few other free components that helped bring this bike back to 1948 status.
Jim’s real reward, though, is in what he learned about the model that started out as a war refugee. “I learned a lot about how they built bikes in those days, from building this bike,” he said. Indeed, one of those inside tips was the process of Parkerizing, a metal rust-proofing treatment that was especially common from early post-war motorcycles like the S-125. Jim did his own Parkerizing of the bike’s hardware, too, and he gives partial credit for his success to his wife: “I Parkerized the parts in our kitchen’s oven,” he says, pausing, “my wife was so understanding.”
The end result is a mongrel 1948 S-125 that is, essentially, a conglomeration of 1948 parts, including NOS and reproduction components. More to the point, the little bike gets ridden. In fact, I first spotted Jim and his S-125 while I was on my way to lunch in Temecula’s Old Town tourist district. He and I got to talking, and soon enough I concluded this little black beauty needed to be featured in Motorcycle Classics.
Firing up the engine is simple and easy, too. I know because Jim let me ride the little tiddler. Just turn the ignition switch on the tank, tickle the carb ever so slightly, and then give the kickstart lever a swift kick with your left foot. After a little warm-up the engine responds … slowly … to throttle input, moving you ever so gently forward. Shifting is slow, yet precise, and don’t expect your arms to be ripped from your shoulder sockets. However, the ride is, in a word, fun. The world passes slowly by, and by the time you click the shifter into third — and top — gear, you’ll feel transported back to a time when most motorcycles represented the simplest of mechanical engineering and design. Heck, the ride might even put a feather in your face to seek your own old bike to restore. After all, it was that curious moment that led Jim to restore this cool little bike from the past. MC
So what about that Hummer name anyway? Well, it actually has its origins at a Harley-Davidson dealership in Omaha, Nebraska, when, in 1953, owner Dean Hummer sought a way to attract buyers for the little 2-stroke models sitting on his showroom floor. His solution was to discount the bikes so low that potential customers couldn’t refuse the offer. As time went on, Hummer’s dealership led the nation in sales, and soon enough Harley-Davidson’s key managers took notice.
Eventually, Harley-Davidson developed a cost-cutting model based on the S-125, and so for 1955 the Model B was added to the lineup. It was powered by the original 125cc engine, and shared floor space with the ST and its 165cc engine. To keep costs down, the Model B lacked a front brake and battery-powered lighting and ignition. Chrome trim made way for blacked-out components (who says Harley’s current Dark Custom concept is new?), and of course the smaller-displacement engine helped put a cap on the MSRP as well.
Harley-Davidson didn’t take full credit for the Model B, either, and so named it the Hummer, in recognition of Dean Hummer and his record-breaking sales run of previous years. Obviously, too, the Hummer moniker struck a nerve with enthusiasts, and to this day many people mistakenly refer to all 125-175 models as Hummers. — Dain Gingerelli