(8/11/2007)
Jawa boxer twostrokeOur Motohistory Quiz #43 depicted an unusual Jawa road racer, circa 1969, powered by a two-stroke opposed twin, pictured here. Even more unusual, the engine was mounted in the frame with the cylinders pointing upward and downward, presumably to reduce frontal area by making the machine as narrow as possible. Cooling was not a problem because the Jawa engine had been fitted with liquid-cooled cylinders and heads, carved from billet (See Motohistory News & Views 8/3/2007). German reader Ralf Kruger won the quiz, and we exchanged a few E-mails about the rarity of boxer two-stroke motorBMW R10cycles. He sent me some images of the BMW R10, a post war prototype with a 100cc boxer two-stroke that was never put into production. The R10 engine is pictured here.
I once had the privilege of seeing the R10 prototype at the BMW Museum in Munich, and I think it is a good thing that this little motorcycle never made it to the assembly line, because it might have done serious damage to BMW's stalwart reputation. By all parameters BMW, it was pretty pathetic! So where, you might wonder, would BMW come up with such an idea at the close of the Second World War? Well, perhaps it was because toward the end of the war they produced a small boxer two-stroke which functioned as a starter for jet aircraft engines. Included hereBMW boxer twostroke is a photograph of one of these engines, currently on display at the Bench Mark Works Museum in Sturgis, Mississippi (See Motohistory News & Views 7/16/2007 for our story about Bench Mark Works).
I began to ponder how really rare the boxer two-stroke configuration is in motorcycle design, or at least there are not many I am aware of. I can think of one other, which is the MZ BK350, a tidy little street machine built in Eastern Germany from 1953 through 1958. Its engine is MZ BK350pictured here. So this gives us three; two of which never went into serial production. Although Soichiro Honda and his competitors in Japan were strongly influenced by 1950s and early ‘60s German motorcycle design, I am not aware that any ever built a boxer two-stroke. If any readers are aware of other examples, please let me know, and send along photos if you have them.
Photo of BMW R10 provided by Ralf Kruger.
Photo of Jawa road racing engine provided by Virgil Elings.
http://www.motohistory.net/news2007/news-aug07.html
This is the interesting blog that got me started:
http://davedragon.rilysi.com/2008/12/bm ... -2008.html
And here is a picture of it from BM Bikes:
Check out his goggles! They look like winter goggles.