This Is How an Engine and World War II Changed Motorcycling

italjet super sport 50
How One Engine Changed Motorcycling ForeverThe Enthusiast Network - Getty Images

Motorcycles weren't always the monocoque-framed, wide-tired, 200-mph speed machines you see today. In fact, the origins of the motorcycle date back to two-wheeled experiments in personal transportation stemming from the bicycle. And motorcycling has historically been about reducing the cost of getting from one place to another, though the joy induced by riding has always been a welcome side effect.

To that end, modern motorcyclists like myself owe it to our riding forebears to learn our two-wheeled history. And a significant piece of the complex puzzle that has led to modern motorcycling started before World War II.

As Ryan from the motorcycle-focused YouTube channel FortNine explains, the development of powerful, reliable two-stroke engine construction is directly linked to the onset and end of World War II. Specifically, a model known as the RT 125 made by German manufacturer DKW was initially the only model to benefit from the new two-stroke technology, known as schnuerle porting.


Named after German engineer Adolf Schnürle, the process of schnuerle porting was a revolutionary way to completely push exhaust gases out of the combustion chamber. By adding two intakes and one exhaust on the same side of the cylinder, schnuerle porting (also known as loop scavenging) reduced the amount of trapped exhaust in the upper combustion chamber, a common problem found in a cross-scavenged two-stroke engine.

dkw rt 125
An early DKW RT 125 model is shown here, with a particularly precarious looking pillion seat. ullstein bild Dtl. - Getty Images

"The two-stroke engine has gained increased importance over the course of time compared to the four-stroke engine due to the great simplicity it assumes under certain circumstances. The two-stroke types with slot scavenging, in which the exhaust and scavenging slots are controlled by the calving, are very advantageous," Schnürle writes in his 1924 patent application, which was approved in 1930 but not before DKW acquired the rights to the loop scavenging two-stroke technology in 1929. With DKW being the only manufacturer legally allowed to produce a motorcycle with a period-efficient and largely powerful engine, the future of competitive motorcycle options was looking grim for consumers.

Cycle World's long-time editor and motorcycle industry legend Kevin Cameron wrote about the disadvantages of cross-scavenged two-stroke motors back in 2017.

"The idea was that during the time taken by the intake flow to traverse this loop, the exhaust process would finish and the rising piston would close off the ports, trapping the volume of fresh mixture still in the loop. These problems limited power and compromised reliability, such that the search for two-stroke power in the 1920s and ’30s turned to such complexities as two opposed pistons in one cylinder, controlled by two cranks, or two parallel cylinders sharing a common combustion chamber, plus the use of an external scavenge blower in piston or rotary form. Such engines were neither simple nor cheap. This explains why DKW management saw value in Schnuerle’s scavenge scheme."

What does all this technical gibberish about two-strokes and pre-war German engineering have to do with modern motorcycling? Well, DKW held onto the patent for schnuerle porting throughout World War II, using it to produce motorcycles for the German armed forces (Schnürle himself was complicit in Germany's war effort and produced radial aircraft engines for the Luftwaffe). However, following the Allied victory in 1945 and the subsequent annulment of the Axis manufacturing infrastructure, the patent for schnuerle porting was distributed throughout the globe. As a result, nearly every Allied manufacturer created its own spin on the revered DKW civilian RT 125 and military NZ350.

the post office delivery services london 1933
LondonPA Images - Getty Images

Specifically, the DKW manufacturing facility in Zschopau, Germany, survived the war unharmed and fell into Soviet territory, with the full DKW production line and machinery shipped to Izkevsk, Russia. A knock-off version of the RT 125 soon came around, known as the M-1A Moskva thanks to its new Moscow-based production facility. Across the Baltic and North Seas, BSA had been handed the rights to UK-based production of an RT 125, pumping out the hit BSA Bantam. Production of the Bantam ran from 1948 to 1973, with almost half a million units produced.

Even Harley-Davidson produced a model based on the RT 125, known as the Model 125. To suit American consumers, the bike's design had been mirrored to place the shift pattern on the left side, as riders wailed all three horsepower through its four gears. Harley went on to produce a larger 165cc version before reverting it back to 125cc and naming it the Harley-Davidson Hummer.

harleydavidson hummer
Harley-DavidsonImprobcat - Wikimedia Commons

It wasn't just Allied forces who ended up benefiting from the open-sourcing of the first reliable two-stroke engine. In fact, Japan also managed to produce copycat versions of the RT 125, though by more difficult means. By reverse engineering an RT 125, Yamaha was able to produce the YA-1, which it released in 1955—the first ever Yamaha. Italy followed suit and created a variety of national off-shoots of the design, including the Mival 125 T, Maserati's Tipo 12, and the ItalJet SuperSport 50.

exhibition on 100 years of dkw motorcycle construction
The Museum of Saxon Vehicles in Chemnitz, Germany, hosted an exhibit about DKW Motorcycles in 2022. picture alliance - Getty Images

Regardless of the production country, these glorified two-stroke mopeds, sporting substantial frames and drum brakes, became instant hits around the world. The pricing was right, the size was right, and it was easy for nearly every manufacturer to make. And because so many people could get their hands on one, a cult culture of racing these bikes soon followed. This sort of two-stroke technology was later reworked by East Germany defector and MZ Motorcycle's engineer Ernst Degner during his time at Suzuki following the war, allowing both Suzuki and Yamaha to push the boundaries of 125cc racing at the time. Another East Germany-branded MZ Motorcycles engineer Walter Kaaden is also credited for such advancements, in which adding a third transfer port opposite the exhaust port further maximized efficiency.

While this era of motorcycling history is ever complex, the lesson to take away from the FortNine video and the accompanying context is that the Allies' victory in World War II is directly linked to the fair expansion of the two-wheeled industry since then. Though two-stroke bikes aren't exactly popular these days, the development of four-strokes is in part owed to the side-by-side development of both powerplants in the 20th century. And if you ever get a chance to ride a DKW RT 125 derivative, just remember you're riding on a major piece of history.