Ahh, two-stroke engines. Many people associate the sound (and smell) of a two-stroke engine with yard equipment, but to motorcycle fans, it means something else entirely: performance. See, before emissions regulations were as strict as they are now, two-stroke motorcycles ruled not only off-road but also on-road and, more importantly, on race tracks. But how did that happen?
The success story of the two-stroke engine is one that involves Nazi missiles, betrayal, industrial espionage, and more intrigue than you can imagine with a bottle of castor oil, and it’s beautifully presented in this 20-minute film from youtuber bart.
The first two-stroke engine was created in Scotland in 1881, but it wasn’t until 1908 that they became practical for use in motorcycles and scooters. These engines were used because they were simple and cheap to produce, but there was a noticeable limit to their performance, causing most high-performance and racing motorcycle manufacturers to use four-stroke engines.
This changed when a German rocket scientist, Walter Kaaden (the video claims he worked on the V1 missile, but this is not true. He worked on the Hs 293 remote controlled anti-ship missile which was responsible for sinking dozens of allied ships along the way) he started messing around with a DKW 125cc motorcycle after the war. He eventually took up this bike race which caught the attention of the IFA racing team (which DKW was taken over post-war), who hired him to run their racing efforts.
Kaaden’s greatest contribution to two-stroke engine design was the perfection of exhaust expansion chamber, which would allow the engine to breathe better and increase power by around 20 percent over engines with normal exhaust pipes. The technology is still in use with modern two-stroke engines today.
Eventually, Kaaden was brought on to work for East German motorcycle manufacturer MZ where he continued to innovate and boost two-stroke power outputs. In 1961, Kaaden’s MZ 125cc racing engine became the first naturally aspirated engine to produce 200 horsepower per liter of displacement (that’s 25 hp for you non-mathletes out there), a figure that’s still insanely impressive today.
Of course, nothing gold can stay, and eventually, MZ’s top rider, Ernst Degner, inked a secret deal at the Isle of Man TT with then-struggling bike manufacturer Suzuki to give them Kaaden’s technology in exchange for 10,000 GBP (that’s around $183,143.57 in today’s money) and a full factory ride for the 1962 season. Degner defected from the East German Republic and MZ motorcycles at the Swedish Grand Prix in 1961. He made his escape in the trunk of a car.
Two-stroke bikes remained the dominant force in motorcycle grand prix racing until 2002. After that, the rules were restructured around a 990cc four-stroke engine layout. It’s now rare to hear the classic “ring-a-ding-ding” exhaust note from a two-stroke motorcycle anywhere except in the dirt due to emissions, and even that is becoming less common. Still, they were important and, dammit, they’re great.