Ahh, two-stroke engines. Many people associate the sound (and smell) of a two-stroke with yard equipment, but for motorcycle fans, it signifies something else entirely – performance. See, before emissions regulations were as stringent as they are now, two-stroke motorcycles dominated not only off-road but on road and, more importantly, on racetracks. But how did that happen?
The story of the success of the two-stroke engine is one that involves Nazi missiles, betrayal, industrial espionage and more intrigue than you can shake a bottle of castor oil at, and it’s laid out beautifully in this 20-minute film by 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 cap on their performance, which caused most manufacturers of performance and racing motorcycles 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 isn’t true. He worked on the remote control Hs 293 anti-shipping missile which was responsible for sinking dozens of Allied ships during the way) started tinkering around with a 125cc DKW motorcycle after the war. He eventually took this bike racing which caught the attention of the IFA (which DKW was absorbed into post-war) racing team, which hired him to run its racing efforts.
Kaaden’s biggest contribution to two-stroke engine design was the perfection of the exhaust expansion chamber, which would allow the engine to breathe more effectively and which increased 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 remain the dominant force in motorcycle grand prix racing until 2002. After that, the rules were restructured around a four-stroke engine design of 990cc. It’s rare now to hear the classic “ring-a-ding-ding” exhaust note of a two-stroke motorcycle anywhere except on dirt because of emissions, and even those are becoming less common. Still, they were important, and damnit, they’re pretty cool.