By Peter Tanshanomi
As far as engine layouts go, you can’t get much weirder than the BK350’s air-cooled two-stroke boxer twin. But when you think about it, the format makes lots of sense, at least by the somewhat twisted Eastern Block way of thinking common behind the Iron Curtain.
The lack of overhead valves helped keep the overall width of the horizontal cylinders fairly narrow, and the two opposed pistons provided perfect primary balance. Since the two cylinders shared the same intake timing and worked in concert to create the precisely timed vacuum/compression/transfer cycle required to feed air and fuel to the combustion chambers, they could therefore share a common crankcase cavity. As a result, the cylinder offset was unusually narrow for a two-stroke. This helped quell secondary vibration (or “rocking couple”) as effectively as a 4-stroke boxer, which is to say, better than any typical two-stroke. Most importantly—given the prevailing social and economic conditions in Soviet satellite countries in the ’50s—it achieved this smoothness while remaining simple, simple, simple.
The design for the 350cc BK350 was originally proposed to DKW during World War II, but the design was rejected as inferior to the four-stroke boxer designs already in production. Once the Reds gained control of East Germany, the utter simplicity and utility of the two-stroke design was viewed more favorably by Der Kommissar than it had been by those bourgeois engineers of the former Reich. By the time the BK350 went into full production in 1953, DKW had morphed into the commie-run IFA. The design would be produced until 1959, two years after IFA was renamed “Motorcycle Zschopau,” or MZ as it became better known.
With only 15-17 horsepower, the 350cc boxer was no powerhouse, and the electrics were a bit crude, even by contemporary standards. But it was attractive, rugged, durable, easily fixed with basic tools, and could be had with either a standard 4-speed transmission, or a set of lower ratios for sidecar duty. The engine’s resulting appearance is minimalist, yet surprisingly pleasing, very sculptural and undeniably elegant.
The BK350 remains the most successful two-stroke boxer twin ever made…not that that’s saying all that much.
Jeff Glucker
Seems as tho the write does not like the bikes from behind the iron curtain and this one in particular. Wonder why he bothered to write about it.
Still he wrote a very informative article about this intriguing machine.
I wonder how you got the impression that he doesn’t like former East-Block motorcycles or this one in particular, when he described this machine as: ” …… it was attractive, rugged, durable, easily fixed with basic tools,…..”
Ha, that is more than what you could expect from the majority of Britbikes of the same vintage.
you have a good point.