How the cold war spurred two stroke engine growth

A two-stroke engine is a type of internal combustion engine that completes a power cycle with two strokes of the piston in one revolution of the crankshaft. This is in contrast to a four-stroke engine that requires four strokes of the piston to complete a power cycle.

Two-stroke engines are preferred when mechanical simplicity, light weight, and high power-to-weight ratio are design priorities. They are lubricated by the traditional method of mixing oil into the fuel, and they can be worked within any orientation as they do not have a reservoir dependent on gravity.

This makes them suitable for their use in handheld tools such as chainsaws. Two-stroke engines are popular in small-scale propulsion applications such as motorcycles, mopeds, and dirt bikes.

The first commercial two-stroke involving cylinder compression is attributed to Scottish engineer Dugald Clerk, who patented his design in 1881. On December 31, 1879, German inventor Karl Benz produced a two-stroke engine for which he received a patent in 1880 in Germany.

However, the first truly practical two-stroke is attributed to Yorkshireman Alfred Angus Scott, who started to produce twin-cylinder water-cooled motorcycles in 1908.

Credit for developing the modern high-output two-stroke engine to its full potential usually goes to MZ engineers in former East Germany. MZ is an abbreviation of Motorenwerke Zschopau, the firm named after their home city, located about 12 miles from the Czech border.

Two-stroke engines had been around since the dawn of internal combustion, regularly trading dominance with four-stroke power. German engineers devoted great efforts to developing high-performance two-stroke engines.

As early as the 1930s, DKW achieved some impressive results, winning motorcycle races all around Europe with a wild supercharged five-piston twin-cylinder (two pairs of pistons shared cylinders siamesed at the top, and the outsized fifth piston drove the compressor).

At the time, many two-stroke engines relied on supercharging to develop their race-winning potential, but when supercharging was banned after WWII, a two-stroke did not vie for the top laurels until MZs effort in the early 1960s.

In the 1950s and 60s, communism and capitalism struggled for supremacy in every sphere, each trying to outdo the other, even on Grand Prix racetracks.

After WWII, Europe set about rebuilding shattered plants. In the early 1950s, the metallurgical, engineering, and manufacturing breakthroughs that had been developed on a war footing were adopted by the civilian industry. One side effect was that racing motorcycles improved rapidly.

Behind the Iron Curtain, however, Soviet-style centralised planned economies put almost all their engineering talent to work on military projects. The result was that civilian vehicle production lagged, and development was almost non-existent. Look at the East German Trabant car, as an example of just how ghastly their vehicles were.

And, as bad as they were ordinary workers had to wait years to get one. But because communist fans needed the diversion, motorcycle racing remained highly popular behind the Iron Curtain. Max Oxley’s book Stealing Speed illustrates the difficulty of life in the Eastern Bloc.

Walter Kaaden was MZs chief project engineer, and his intuitions proved fundamental when it came to extracting ever-increasing output from two-stroke designs.

Kaaden and MZ made breakthroughs with their resonant expansion chamber exhaust systems and the time/area relationship in the two-stroke’s volumetric efficiency.

After ending the 1961 World Championship a strong second place, MZ factory rider Ernst Degner fled East Germany and took Kaaden’s drawings with him, delivering them to Suzuki.

From then on two-strokes began their domination of all forms of motorcycle sports, track, road race, motocross, ISDT, enduro, and trials. Only endurance remained out of reach, although Yamaha’s TZ 700 gave the competition a solid scare at the 24 Hours of Bol d’Or.

With the exception of Honda, the Japanese factories focused on further evolving two-stroke technology, reaching outstanding levels of specific power output.

Suzuki, Yamaha, and Kawasaki all constantly improved their engines, developing and refining every possible kind of induction system from the traditional port induction to rotary valve, and using reed valves in both the cylinder port and in the crankcase. The final results were astonishing.

After years of Japanese dominance, a sort of resonant two -stroke return wave revitalised Europe’s motorcycle industry. Highly competitive two-stroke engines appeared, mostly from top German and Dutch technicians like Jan Thiel, Jan Witteveen, and George Moeller. These men further refined the two-stroke and achieved winning results on the track, particularly in the lower displacement GP classes.

The two-stroke’s continuously progressing potential, both in Europe and Japan triggered a sort of euphoric enthusiasm for further research and experimentation. And given the results that four-stroke engines were able to achieve by adopting fuel injection, a massive amount of time and money was devoted to fitting two-strokes with the latest electronically managed fuel-injection systems.

Limitations soon appeared. Two-strokes needed very powerful ECUs in order to manage three-dimensional fuel-metering programs necessary to deal with the two-stroke’s range of engine speeds, which is wider than a four-stroke’s.

In the meantime, four-stroke technology advanced so much that they were nearing the volumetric efficiency of the two-stroke. That combined with the narrow power bands associated with two-strokes and ever more stringent environmental pollution regulations, put the two-stroke at a distinct disadvantage.

Four-stroke motorcycles were more tractable in putting the power to the ground with their wide power bands and gradually from 2002, they took over GP racing and other forms of motorcycle racing.

If it were not for the defection of Ernst Degner in 1961, it is unlikely we would have witnessed the monumental development of the two-stroke engine.