Tuesday, September 30, 2008


Perhaps every racing motorcycle has a unique story to tell, but this '39 DKW SS350 production racer has a very interesting tale. When found in Sweden a few years ago, it had previously only had two owners, and was originally a Polish racing machine. 'Why Poland, and how could it have been exported there after the war began?'

The story I heard; a Polish horticulturist (also an amateur racer) had perfected a variety of black roses which were unique. German officers were quite keen customers for his blooms, as they were especially appreciated by their Parisian girlfriends... one well-connected officer asked the Polish fellow how he could reward him for his special efforts on their behalf (the girls must have really liked those flowers!) - he wanted a racing DKW. So, this motorcycle was invoiced to him 'without a petrol tank', but the tank with the bike is from a Works racer, and must have come along with the deal as a special favor.

The DKW was dismantled when things turned sour for his patrons (and for Poland), and was eventually smuggled out of the country to a Swedish collector in the 1980's.

I enjoyed riding near this machine on the Hockenheim circuit; it has no 'ring-ding' of modern two-strokes, but emits a low and raspy bellow. The SS350 is water-cooled and has 'twin cylinders', but four pistons, as the two pistons/barrels for each combustion chamber are used to 'time' the intake/exhaust cycle accurately and push both the incoming and exhaust gases to the right places at the right time. I'll go into how this works in another post, but DKW weren't alone in using two pistons per 'cylinder' - even the last Sears Allstate (Puch) machines used a similar system in the late 1960's - some people call them 'twingles' (twin piston/single cylinder), although I suppose the DKW would be called a 'fourtwin'. These racers also have a Ladepumpe under the the engine, which is a separate cylinder (and crankshaft, on the Works machines) used to compress air into the crankcase - a kind of supercharger for two-strokes. Thus, while this motorcycle is technically a twin-cylinder two stroke, mechanically it is a 5-piston machine - hardly a 'simple two-stroke'. The SS350 produced around 34hp, and used magnesium for the crankcases, gearbox case, and brake hubs, and was what DKW offered to the public for racing. According to Wolfgang Schneider, this complicated multi-piston two-stroke engine is only competitive for racing when the extra 'push' of the Ladepumpe piston is used. The similar Works Ladepumpe 'UL350' racer produced 38hp, but by 1939, the Works machines used a rotary supercharger, and this 'US350' model produced 49hp. And clearly, I need to make a proper timeline for these racers!

DKW joined forces with Audi, Horch, and Wanderer to form Auto-Union in 1932 (making the four 'rings' still seen on Audi), while DKW was the largest motorcycle manufacturer in the world (and Auto Union the second largest motor vehicle mf'r). The DKW archives and many of their works racing machines can be found at the Audi museum in Ingolstadt. Audi also has a small museum in their showplace in Neckarsulm, home of NSU, which was absorbed by Auto Union in the 1969. There is a very nice collection of racing NSU machines in Neckarsulm; photos of that trip are here.


Anonymous said...

Hi Paul,

home again,I hope more save than the trip you had to cpme here.Nice Story about the DKW SS 350.
Sorry but its not a Twin Cylinder unblown!You have written that twe Works is supercharged,so the people mean this 350ss is a as usual " Sucker".

I will tell you that it is also a Supercharged "Ladepumpe" you can see the big Cylinder underneath the Crancase.
It´s right that it has Two Cylinders,but its the Double Piston System,so each Cylinder has two Piston,Two Cylinders have 4.
So with the Charger we have 0ne crankshaft,five conrods and 5 Pistons.
The 350 works and Produktion are very similar,some works had different Blowers,and for the 500 they
would use a Prototype with 3 Cylinder 6 Piston and a big Blower,but BMW was the unbeatable (after many Years in researching and performing this Engine during the 30ts)in the 500 Solo,also Gilera was ready before DKW could bring this Type.Well NSU was trying to bring there 350s and possible also 500cc on the road,but they where unlucky with there Chargers and maybe some other poor working Things,and so the mostly retired with these heavy wheigt Steel Monsters until the big War began.
The idea for this brand new 6 Piston DKW 500cc was the result to become the performance of this last 250 Works which had a Rotation Blower and two Cylinder 4 Piston Engine,ther where absolutely unbeateble( against the old fashion Excelsior ) because for example the Supercharged Benelli 4 wasn´t ready intime.I dont know if any part of these last 500 is still exist.You know who enter this Factory in 1945.
An earlyer 500 4 Piston(onkly bigger Pistons like this 350) wasn´t competitive enough in the Mid 30ts,so DkW reduced there Activities to win the 250 European Championships and won Internatinal races and National titles with there 350cc Wors(a reduced 500) in 1939 they built a Handfull 350SS Production,two of them you saw in the Pit at Hockenheim,another(Red/black Tank) in the Museum there.

(together with the 175cc and Sidecar 600cc won DKW 10 European Titles,most in the 250cc)

Its a little bit unusual,but this Maschine has arond 34 H.P. the Works over 40 and the Sitecar(600cc) nearly 50 H.P.
The Works have lighter Chassis Parts as Fenders with Alloy/ Magnesium etc) .
But the Sidecar Bike was fobitten by Germans Motorsport Association after the 1937 Racing Season in fact of several deathly accidents in this Class.
Remeber that also the fast BMW´s had Superchargerd Sidecars in these Years.
For more Details ask Stefan Knittel.



Anonymous said...

Hi Paul,
well done your Update,but the crancshaft of the production is one Piece.
You saw the drawing of the works ULD from 1937/1939 which has a special crankshaft for the blower Piston.They have the carburettors in Front of the engine,some work with Disc ore Rotary valve and also with " Membrane"
the SS 350 a simple version without rotary valves hold the manifold behind the Cylinder,and special ways to the bottom through the 2 way working ladepumpe.one side pump it to the left cylinder,the other side to the right.Of course its a two stroke,but power is coming after all 180 degrees what make these enguines running like a powerfull Turbine.

The Productions SS 250 and SS 350 has one crankhaft pressed and srewed into one piece. While the 250 production has only two pistons,one hub for the ladepumpe,and one for the splitted Conrods(one Big end,and a linkage for the second Conrod just on the side of the other fitted .)righ hnad the Ignition with his Flywheel ist mounted and on the left the primary Sprocket ist fitted.

When I say that the SS350 is similar to the works UL 350,500,600 and 700, I mean the version which was used from 1934 until 1938.They are realy similar without any rotaring valves.
Works Engines UL 350 has 38 HP
UL 500 has 48 HP
UL 600 for the 600cc (must much more that 50HP)sidecar Class
UL for the 700 Sidecar Class (no Idea how much HP)

Works Engines ULD 350 (two Crankshafts for ladepumpe and Working Pistons) and US 350 49 H.P. which use a rotation Compressor which where used in 1939.
Unbelievible but true,the 4 piston Works 250cc US had 40 HP in the last year of running(1939)while the earlyer ULD had only 30 and the Produktion SS250(two piston had 20 H.P.)
No idea what the Big Banger for 1940 designed 3 cylinder (6 Piston with Kompressor) should have had with 500cc.Must must more than Georg Meiers BMW,but the war made all these plans to Dust.....There was another projekt a opposit 250 s stroke(Two crankshaft) Blown to much more than 50 HP with only 250cc.it was finished after the war by a Privateer in 1949 (Kunhnke)and is now in the AUDI Museum.Fastest 250,and loudest Vintage Bike I ever saw on a track with its 4 megaphones!

Now again how the SS 350 works:
Two Hubs where for the Conrods of the Working pistons.Specials con rods where used,only one big End each Main Conrod(the rear) has a little" Knee" linkage where the second Con rod is fitted.This moves not the same way as the other.
So the Left and the right cylinder has one spark plug, two cylinders(Two main cylinderheads on each side, looks like a bathtube),one front Piston Intake,one rear piston exhaust(Work like a Fourstroke,that ist a kind of Valve to have exact Timings,so the Mashine works perfect with a Megafone(no power is getting out like in these Schürle Machines) it works only competitive when you have a Blower.
The special is that the rear Conrod ( it has the big end with needel rollers running on his Crankpin)is running 15 degrees earlyer than the intake Conrod with his piston.that means it opens earlyer the exhaust,but close it also earlyer while the intake piston let still the copressed mixture into the combustion room.

The Puch engines are not the same,there is another double piston system used by German triumph Nürnberg,whis has just one Conrod one piece with one big end and on top it ist Slittet to hold two pistons called a Fork Conrod.These simple Double piston engines where sold in 125 and 250 road Bikes,little faster that normal schnürle engines,but the need also much Fuel and the Engine rebuilt needs more money than normal One piston Systems.Triumph Germany merged later with ADLER and stopped the manufacturing of these Bikes to produce typewriter machines and other Office Stuff. It sucks the Mixture in the Ladepumpe,and it Pressed it through the Front Pistons when they open intime when its needed.The Two pistons Compressed this while exhaust close his ports earlyer (this is possible because the con rod is Splittet with an additional linkage direkt over the common Big end for both)After Spark plug fired this up,the exhaust opens ealy,and the waste goes out.While Intake Piston give way for the new mixture,which is well compressed by the big guy in the Bottom the same procedure goes on.
The right cylinder makes this 180 later,its not a twin ,needs no big Flywheel as these british 4 strokers with twin system(or even a Harley)
They are running absolutely without vibrations,and the power comes from low Revs very good over the whole range,and the power is perfect to handle,even in rain where most 4 strokes where little more slippery on there rear wheels.
DKW took a long research and millions of Reichsmark until this works perfect.Two expensive for normal road Bikes,and of course needs a lot of fuel(look at these big Original around 30 liter Fuel Tanks)

Hope you can imagine now how this works. Wolfgang.