For a long time, before pollution regulations and sporting regulations put them offside, two-stroke engines divided the motorcycle market with their cousins to fours.
Really in the competitive field they dominated the scene for a long time in all classes, both in speed and off-road, and they would continue to do so if at some point i regulations of the FIM.
In the history of the motorcycle, alongside the most celebrated four-stroke models, there have been many others, almost always less expensive and of smaller displacement, but often much more popular, which had a two-stroke engine.
This for decades and decades, during which they they were considered real poor relatives of the 4Ts.
This except a few exceptions, which in the pre-war period were mainly due to Scott, at the DKW (which had models even of 500 cm3 and with water cooling) and to the Puch.
As for racing, however, the situation was different and the DKW with its formidable bikes supercharged with split cylinder it came to be almost unbeatable in the 250 and 350 classes in the late 1930s.
In the post-war period, many old and new manufacturers turned decisively towards the 2-stroke for the smaller displacement models, destined for greater diffusion.
The major simplicity and low cost they were extraordinary strengths (performance, however, generally was slightly lower than that of the 4T).
The DKW RT 125, designed in 1938 by the great Hermann Weber, showed the way to everyone. Washing was the classic Purr with tangential currents and with piston without deflector, of which the German company held the patent. The bore and stroke measurements were 52 x 58 mm and the transfer ducts were two.
Simple, extremely robust and capable of providing excellent performance, this bike was a true concentrate of rationality. And in fact, the war ended has been copied by everyone. Many manufacturers have also been “strongly inspired” by it.
The Yamaha has never hidden the fact who, once he decided to enter the motorcycle market, simply created a replica of the German single-cylinder.
As for racing (supercharging had been abolished) it was thought that in the lower classes the 2Ts could have their say. In particular, it was common opinion that in the 125 they would easily defeat their four-stroke rivals.
The Global bialbero appeared in 1948, however, has shown that things were exactly the opposite. The main competitors, namely the Morini and the MV Agusta, so they hurried to make 125 four-strokes too. For several years there have been engines of this type (i.e. those of the three Italian houses plus the splendid NSU title winner in 1953 and 1954) to dominate the world championship.
In Germany, however, some thought that 2T were not lower. It was just necessary to develop them.
The DKW was a major player in post-war reconstruction, producing an extraordinary number of simple, robust and reliable single cylinders.
Competitions were in her DNA and as soon as it was possible this house resumed competitive activity. His most remarkable achievement was one 350 with three 75 ° V cylinders and crank pins arranged to have the useful phases evenly spaced.
The V-shaped architecture made it possible to contain the transverse dimensions of the engine while having the cylinders optimally cooled thanks to the extensive finning and despite having ample space for the transfer ports (which in the 2T increase the width of the cylinders).
In 1955-56 the DKW 350 was the most powerful and fastest bike of its class. However, she was grumpy to drive, had a high consumption and a reliability that was not exactly impeccable, at least initially. And then the riders weren’t exactly the best in the world championship.
In short, many placings have arrived but as for successes …
To the German house goes the great credit to have first replaced the megaphone exhausts with those a expansion. Of course they weren’t like those developed later for the two-stroke competition but they already had a noticeable increase in the section followed by a counter-cone. Appeared in 1952-53 in a rather rudimentary form, they are to all intents and purposes considered the ancestors of modern expansion pots.
It was beginning to be understood that by creating a drain with an appropriate conformation it was possible to improve performance by using pressure waves. The basic idea was to create a positive reflected wave for stop the flow of fresh mixture from the cylinder through the exhaust port, still open after the transfer was complete.
Another house that, even without seriously committing to a competitive level, has left an important mark on the duetempistico field was the Adler.
This Frankfurt company in the 1950s produced excellent two-stroke twin-cylinder engines with an extremely advanced design. His MB 250 (bore and stroke = 54 x 54mm, like most modern 2Ts) it was taken as a model by Yamaha when the Japanese company decided to create a two-cylinder model of this displacement, and this speaks volumes about the validity of the project and the original construction.
The beautiful racing version of the German motorcycle appeared in 1953 and two years later was developed by also adopting the water cooling. Thus also in this case indicated an important road, which was subsequently taken by all the manufacturers of two-stroke racing engines.
What really turned the two strokes, leading them to overtake their cousins to four in terms of performance, was however the MZ which has thoroughly developed expansion drains and, above all, launched the rotating disc suction. (Keep it going)
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