Interesting 2-Stroke Engineering

I often read articles on interesting engineering. As of late, the subject of the Supercharged 2 Stroke. Honestly the more I study the drawings and articles in this particular instance, the more my head begins to hurt. Try wrapping your heads around the complexity of these machines. They are no joke, not simple by any means and not new either…we are talking 1930’s tech but still.

I used to attribute the fearlessness of and the zeal for complexity, to the Japanese, but I think Zee Germanz might actually have them beat. Amazing stuff really, if you are into mechanical contraptions, as I happen to be.

I’ve read the article below several times and I still cannot fully wrap my head around these DKW machines. I am truly in awe. Just thought some of you might appreciate the read and the concepts.


The operation is actually far more simplistic than that of a 4 stroke but the math required to pull it off efficiently is where it gets complicated. Properly managing back pressure waves through the use of an expansion chamber to enhance power through a specific RPM range? Getting fuel into the engine is easy, keeping it from flowing straight out the exhaust port is the hard part. Anyone can turn an air compressor into a 2 stroke engine with the right knowledge and tooling though.

On second thought after grazing through that article I was at first glance convinced they have some voodoo going on there. But upon further inspection the concepts all make perfect sense. But for their time? That’s pretty ingenious stuff.

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It looks like they made a lot of use of the split single design, which was essentially a folded opposed piston engine, one piston uncovered the transfer ports and the other the exhaust ports, no way for the fresh charge to just short circuit out of the exhaust ports.
In the 1970’s, I was allowed to take a 250cc Puch Allstate split single for a short ride. While not exactly a rocket ship, these were said to get excellent fuel economy for a two stroke.

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Yes, @B.L.E I’ve heard of that Puch split twin, never seen or ridden one. I believe Puch was mentioned in the DKW article as well as a contributor in design or concept.

Each time I look at those drawings or pictures of engines I keep thinking… “wasn’t anyone concerned with more moving parts or complexity ?” They just did whatever they dreamed up and machined beautiful parts to make it function…and reliably at that ! Its crazy when you think about it. No computers, that was all done by someones skilled hands all from specs on a piece of paper. Can you imagine? I take my proverbial hat off to the skills involved.

One side benefit of having that opposed “pumping” piston is that it doubled as a piston mass counterweight, quelling the vibration inherent in a one cylinder engine. That old Puch I took a ride on did vibrate, like an old Jawa 250 single. When today’s riders take a ride on some of those vintage bikes, they are usually amazed at how much vibration people put up with and regarded as normal in those days.

That’s true about vibration of older machines and people today @B.L.E . On the Supercharged DKW that supercharging piston was moving almost at a right angle in comparison to the “working pistons”. I’m no engineer but in my head, that wouldn’t seem to cancel vibes per say…I’m sure it had an effect, but i doubt it was “cancellation” maybe more like “reduction” of vibes in the end? But I honestly don’t know how that all plays out in physics land.

Still its all ingenious and interesting no matter how you slice it.

I started my career before computerized design. We did everything by hand. Handheld calculators were a huge timesaver. These are a tad earlier but illustrates how computers changed everything…


I have a ton of respect for the engineers and machinists back in the old days. It’s easy to think of things being kind of Neanderthalish but they were actually very precise.

Rod and main bearing rollers in .0002 oversizes for a 1922 Harley for example. One of my old manuals shows engine set-up specs for a 1936 Chevy as being much closer than anything else over the past half century.

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I had a Jawa 250 enduro. Big slug in that motor. During moto-x days when I was riding a suzuki tm 125 and later rm 250, you always tell the big slug singles coming up from behind…

Is that right @ok4450 ? I did not know this, that’s awesome. Again…respect for those skills, because if you could make machine products using the fundamentals the “manual” way like back in the day…you could easily do it with computer controlled machines after a bit of training on how to interface with the computer. I dont think it would work the other way round… computer controlled guys trying to use the manual machine tools, no, I dont think that would play out very well.

Correct. Bearing replacement is done in .0002 increments until the wear limit is reached which is .001. At that point shafts and races must be replaced to restart the process. However, that .001 maximum goes goes for a lot of miles.

It does boggle my mind that apron clad guys in dimly lit shops with zero computers and digital electronics could be so precise over a 100 years ago turning out components accurate to the ten thousandths of an inch.
And a few years ago I watched a show on TV which involved the plant where new Camaros are manufactured. Body is robotically assembled and welded and lasers assure that the body is “within .030 of an inch”. JMHO, but that sounds a bit much if say subframe mounting holes or strut towers are .030 off…


Also think of the watch and clock maker’s back in the day they might not be quite that precise but think of the all the small gear’s and spring’s that had to be assembled and timed just right.

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@Renegade your comment makes me think of my Grandfather… A machinist born in Italy in 1899. He would be a machinist his entire life and I believe he began that career when he was in his late teens early 20’s, which puts it around…the late teens or 20’s of the 20th century.

He only attended school up to the 4th grade yet could still work out the calculus needed to figure out how large a watch gear should be…and how many teeth it needed in order to keep proper time. To a little boy my Grandfather seemed like he was some sort of Wizard based on the things I would see him make and or repair…and as much as possible, I was right there, watching, handing tools over, learning…and (his favorite) turning bolts the wrong way due to a condition he said I possessed called “Lefthandedness”. I outgrew turning the fasteners the wrong way, but never got over the Lefthandedness condition.

As I type this, one of his magnetic base Starrett run-out dials is on my computer desk. I think about those early days every time I look over at it. I have so much respect for the Old School…and I like to think I attended many a class myself…hard not to, with the company I was keeping…Pops lived to be 99 yrs old and I have nothing but fond memories and a lot of early mechanical skills and principles that I can attribute to him. Good times with a great man…

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I have nothing but fond memories and a lot of early mechanical skills and principles that I can attribute to him. Good times with a great man…
That is something that can never be taken away from you. I also have great memory’s of my grandmother’s (both grandfather’s died before I was born) one grandmother was born in 1896 and the other in 1904 funny thing was the one born in 1896 went as far as the 8th grade and became a school teacher she lived with us when I was in high school she tryed to help me with schoolwork but I was not the type for book learning I was lke you the hand’s on type of learner all my grade’s were sailer grade’s below C level I would not trade those memory’s for any thing in this world.

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Boy Howdy… Look at that crankshaft. No CNC there…just a man, his hands, a ton of knowledge and skill…and some serious shop tools. They turned out beautiful work didn’t they?