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From : "Eric & Tracey" <Green.Gables@xtra.co.nz>
To : <tomcatloftis@hotmail.com>
Date : Thu, 10 Jan 2002
Hi Tomcat

I have been digging around and come up with some stuff though that you may find interesting. If you've seen this all before don't yell at me too much. I was talking to a friend of mine who had never heard of the DKW strokers They had some impressive ideas about building two strokes. Now for their day, and I'm talking about the 1930's these things were amazingly quick not to mention loud. This was before the advent of the expansion chamber so they were all running a full megaphone on these things. Apparently on the Isle of Mann as they descended Bray Hill they could be heard across the Irish sea on the coast of England and that's sixty miles away.

Pre-war supercharging was perfectly legal as far as racing was concerned. There was a whole heap of really interesting stuff around that time as people were still experimenting with all sorts of weird and wonderful creations, some worked and heaps didn't. DKW were one of the most inventive around as you will see. Damn I hope you don't know all this stuff or I will feel like a complete and utter jerk. Trying to teach one's grandmother to suck eggs and all that stuff. So excuse me if you do, it's just that it's one of my favourite times because of the diversity they had. Not like today when it's getting hard to tell one from another.
Now I know this may sound weird but one of the biggest problems of the early strokers was blowback and loss of charge down the exhaust, especially when they used the megaphones. So to counter this the designers at DKW came up with the idea of the "split single" two stroke. More or less it was two pistons with one single combustion chamber. One piston controlled the inlet phase while the other controlled the exhaust. Because of the offset on the single crank both pistons would meet at the top at the same time meaning when ignition occurred it would push equally on both pistons, neat eh. Now the Germans being Germans were at the time really into supercharging in a big way. So the next step was to come up with a whole series of different forms of blowing these things. I've scanned of some diagrams to show you. Mostly they used the idea of a third piston in the crankcase itself. This was just a dummy cylinder. It again was connected to the crank but offset again to match the inlet phase of the rear piston. As you can see what happened was that as the inlet opened this third piston was pushed down it's cylinder not only sucking in more charge but also increasing the volume of the crankcases. As the inlet closed and before the transfers started to open this piston on it's shorter stroke would be pulled back into the cases compressing the charge creating more pressure for when the transfers opened, damn ingenious don't you think. Makes me wonder how a supercharging system with reed valve like that would work on an H2. The other type of supercharging they had was with the more traditional vane blower but they used the eccentric vane type.
On the diagram marked 1 you can see that they used a reed valve on the inlet with the supercharging piston behind it. And Yamaha reckon that they invented the reed valve, big joke. The one marked 2 has the same principle but instead of the reed valve they used a rotary valve. Numbers 3 and 4 are just different layout of the same thing that just increased and decreased the crankcase volume. Number 5 is their first type of eccentric vane blower. Now number six I think is really interesting and must have taken a fair bit of lateral thinking to come up with. Again it has the eccentric blower but what they did was to cut the engine in half basically and join it end to end. So what they ended up with was a crankshaft at each end, again one piston controlling the inlet and the other the exhaust. To compression space was the space between the two piston as they met in the middle. So when the thing fired it pushed both pistons apart. It must have been as heavy as hell and the loss of power through gearing it all together must have been huge but I find the thinking behind it amazing.
Now all you have to do is build an H2 motor with that sort of stuff onboard hehehehehehe.
Anyway, personally I belive that the DKW factory should be just abouts top of the list of important strokers of the 20th century. They did more in those years to further the 2 stroke than anyone has since, and this was in the face of the overwhelming dominance of the four stroke which they not only matched but went out and beat the pants off. It's a pity that WW2 brought the factory to it's knees, after all with this sort of thinking it would be amazing to think what they could have turned up if they had kept this sort of forward thinking and imagination up.Pic DKW, Ewald Kluge and his water-cooled 350. You can just see the supercharging cylinder underneath the engine. Pic DKW-1, Ewald Kluge again, this time at speed at the Isle of Mann on his 250. He set the lap record on the tortuous 37 mile course in 1938 at an average speed of 78 mph. This 250 was producing 40 bhp @ 7000. This is one of the rotary valve models.
Pic DKW-2 Just a sketch diagram of the supercharged rotary valve 250 engine.
Anyway I hope that this has been of interest to you.
Eric.