The Simson Story and the Simson AWO 425

Written by Keith Philpot



1856. Moses Simson buys the Heinrich Hammer works in Suhl. Together with brother Loew produces weapons and handguns as Suehler Eisenwerk

1896. The second Simson generation add coaches and bicycles.

1911. Car production begins

1914. Production returns to weapons manufacture which continues at the end of World War 1 for police and military purposes.

1924. Car production resumes.

1933. Hitler decrees production must switch to “ higher goals “. To this end Waffa GmbH is established.

Adolph Hitler had one of these.
Adolph Hitler had one of these.

1933. Waffa GmbH taken over by Nazi “ Treuhaendler “ , trustees. Company renamed Berlin Suehler Waffen und Fahrzeugwerke Simson & Co GmbH. The Simson brand is back.

1935. On racist grounds on 28 November 1935 the Jewish management, which had been reduced to non executive status , was fined 1.75 million Reichmarks on the Nazi grounds of “ Illegally gained profits “ under their ban on Jewish business ownership.

1936. The Simson family flee to the USA. Meanwhile , under the brand name BSW, some 3000 units of motorised bicycles are produced up to 1939.

1939. Production is switched to weapons but another 1500 motorised bicycles are produced up to 1940. The company changes name again to GSW, Gustlow Werke Waffenwerk Suhl.

1 July 1945. American occupation forces withdraw back West behind the Werra river leaving control of Suhl to the Russians. The production facility was dismantled and transported to Russia. However, a repair facility was left standing to produce spare parts for hunting weapons, bicycles and prams for Russian consumption.

5 March 1947. The Simson name returns. This time within a Soviet company name SAG, Sowjetische Aktiengesellschaft Werk Simson or AWTOVELO as the Russians named motorcycle production.

December 1948. Out of the blue the Soviets decreed that Simson produce a 250cc 14PS single cylinder four stroke motorcycle with a unit construction 4 speed gearbox, shaft drive and enclosed telescopic suspension front and rear. It was no coincidence that at nearby Eisenach, now also under Russian control and part of the AWTOVELO group, was a pre war BMW works which had marketed their models as EMW. Coincidentally, over in the West in Munich, BMW was developing its own R25 4 stroke single and the pre war Munich / Eisenach connection was still live.

Nonetheless Simson engineers Helmut Pilz and Ewald Daehn went their own way with the design of the Simson engine as they sought punchy performance.

1 December 1950. The first 1000 units of the AWO 425 ( AWTOWELO 4 stroke 250 ) were produced and promptly despatched by rail to Russia.


1951. AWO 425 released for sale in the DDR ( Deutsche Demokratik Republik ) East Germany as it was known in the West.

1951 – 1955. The AWO 425 became the AWO 425 T , for touring , with the launch of the greatly revised AWO 425 S , for sport , in 1955. This machine was not intended as a machine for the masses with its sale price of 3200 Ostmarks at a time when average wages were some 500 Ostmarks per month. It was targeted at middle ranking party officials and for ceremonial use. Accordingly it was intended to showcase the finest motorcycle engineering in the DDR.


1955 – 1961. Production was abruptly brought to a sudden end , after production of some 124,000 units of AWO 425 T and 84,600 units of AWO 425 S, by the astonishing Soviet decree that henceforth all DDR car and motorcycle engine production had to be 2 stroke only.

Schild Fabrik

 About the Simson 425 S


Messrs Pilz and Daehn went about the design of the 425 S with predictable German thoroughness. Every detail from front to back is by design. The 3.25 x 18 diameter wheels front and back are equipped with full width single leading shoe brakes in 180mm alloy ribbed hubs. Detail here is in the awareness of the need to reduce unsprung weight. But get this. The brake linings are glued to the alloy shoes on the basis that this gives both a greater surface contact area for linings due to the lack of rivet holes plus longer wear as no allowance has to be made for rivet heads buried inside said holes.

Both wheels have quick release spindle mechanisms. The front mudguard has a fender extender as standard. The handlebars come with alloy pullbacks as standard and the throttle cable runs inside the bars.

A friction steering damper is fitted as standard as are parking light plus neutral and ignition warning lights on the headlamp shell. Alloy, non ball ended, handlebar levers are fitted.

The frame is a twin loop steel construction. The reason for this is to create a mounting point across the rear of the gearbox to mount the grease nipple equipped swinging arm. Twin pre load adjustable enclosed rear shocks with 100mm travel replaced the plunger suspension of the touring version. Front forks are sprung for 150mm travel with oil damping. The footrests are height adjustable as is the rear brake pedal for the rod operated rear brake. The

frame is equipped with sidecar mounting points plus sprung side and centre stands. Lockable boxes are integrated on both sides beneath the saddle to contain the electrics on the brake side and the comprehensive toolkit on the clutch side.

The motor is a so called Querlaufer – Cross Runner – sound familiar Honda ?

In order to simplify the take off for the rubber cush mounted shaft drive the crankshaft runs across the frame rather than in line with the wheels. Accordingly the cylinder head is turned through 90 degrees to give a conventional front to back exhaust / carburettor layout.

The engine is of an all alloy crankcase, gearbox, cylinder and head construction. All bearings are either steel ball or needle races. The engine is designed to rev, helped by its square 68mm x 68mm bore / stroke dimensions and to produce 14 PS at 6300 rpm. Key to performance is the cylinder head design. The 2 valve head has 2 different valve types, both of 8mm diameter with 36 mm stems.

The exhaust valve is conventional in side profile but made of a more heat resistant steel to the cooler running inlet valve. This has a so called tulip profile, the shoulders of the head are longer and fatter. Both valves are angled at 45 degrees and run in phosphor bronze guides with different lengths for exhaust and inlet. The valves are sprung by 2 piece hairpin springs rather than coil springs. The rationale is that hairpin springs do not get coil bound in high revving engines.

Cylinder Head exposed but minus bolts to crankcase
Cylinder Head exposed but minus bolts to crankcase

The valves protrude a long way into the combustion chamber as the 7.2:1 compression ration high domed piston has deep cutaways each side to allow clearance for the valve heads.

Fuel mixture is fed to the high cam alloy push rod overhead valve engine via a 26mm diameter remote float, flat slide downdraught carburettor which draws air through a long inlet trumpet sealed into the still airbox under the seat at a design rate of 28000 litres air intake at 80 kph .

Told you that everything was engineered. The result is a motor that does not go Thump, Thump, Thump but rather Bang, Bang, Bang as it exhausts through the 3 part silencer with internal back pressure design. This earned the bike the nickname of Dampfhammer – Steam Hammer – in its native DDR.

Transmission is via a 4 speed gearbox driving through a single plate dry clutch.

4 speed positive stop gear box internals
4 speed positive stop gear box internals
Final drive from shaft to rear wheel
Final drive from shaft to rear wheel








Final bevel drive
Final bevel drive
Camshaft and followers to alloy pushrods
Camshaft and followers to alloy pushrods

A quant touch is that the left side one down three up foot change is positive stop whereas the hand change lever, a left over from the original 1923 engine / transmission layout, is not. This lever describes a long arc dependent upon which gear the gearbox is in. It is nonetheless handy at a standstill to select neutral as shown by the green neutral light on the headlamp shell.

On this machine the original 6 volt electrics have been replaced by a 12 volt power dynamo conversion which dispenses with the original contact breakers and mechanical auto timing device. The machine has ignition light, parking light, brake light in addition to the headlight and horn.

The ignition key is a slotted rod which inserts into the headlamp shell to be rotated to the required position. For rainy days there is a neat Bakelite sliding cover to stop water getting into the ignition hole when the key is removed. However the original electrics are dependent upon a tiny glass 20mm 25amp car interior light fuse held between 2 flat spring connectors to transmit power from the battery.

The original owner’s handbook, which I have, shows just how patrician the Party state was as it unselfconsciously lectures the proud new owner as if of right. How many times, it thunders, have you seen fine machines in workshops because of poor maintenence ? This is why we have provided all the tools you need.

Also, it rants on, how often have you seen spark plug threads stripped ? This is why we have equipped this machine with steel thread inserts for the spark plug.

All this aside another little quirk is that on the clutch side of the cylinder head is a cut out of the finning designed, so the book says, to aid cooling air to transit across the cylinder head.

So here it is. A living relic of a manufacturer, country and ideology all of which have long gone. With the mentality of the time in the DDR it came as a complete surprise in Suhl that Simson production would drop from full operation to zero within 3 months of the fall of the Berlin Wall in November 1989. A few far sighted people at Simson hosted a delegation from Honda in the hope that they would produce their vehicles in Suhl much as they were doing in Italy. The delegation took one look at the long row of ancient, decaying buildings of the still standing original plant and shook their heads. Only one building, Simson’s newest and finest purpose built only 3 years before, aroused interest. Once inside this too was rejected. Simson could not have known, thanks to the way the regime had operated, that in Japan factories were built on the basis of huge open sheds. Simson’s newest building was on 3 floors. That ended all hopes with Honda.

The factory site is preserved as an historic site today. Along one side runs a river. Along another side runs the railroad and beyond that the road to Suhl. All the basic utilities and transport facilities needed for manufacture were there.

What was astonishing was that Simson managed to produce the volume of machines that they did whilst under the limitations that resulted from the puppet Soviet regime that Erich Honecker imposed upon the country for decades. The currency, the Ostmark, was absolutely valueless anywhere outside the country. Trade outside the DDR was restricted by the outside world to the COMECON, Eastern bloc states, plus mavericks like Cuba and some African states. To trade with Eastern bloc neighbours in the desperate quest for basic raw materials Simson had to deal in Export Roubles, a false Soviet currency only accepted within that bloc. But this meant exchange rate losses. So barter was the name of the game. A rail car full of motorcycles would be swapped around several times from one commodity to another until Simson finally wound up with something they could trade for hard currency, the Dollar. Even then the raw materials available to Simson were low grade and of poor quality.

But, back to Simson. The isolation of the DDR gave Simson no choice but to do it all themselves. So they did. At one end of the row of buildings was the casting shop, then the engine shop, the gearbox and so on. The separate buildings are standing now and can be seen linked by sloping bridges through which components would travel onwards. Frames, for example, were slung on hooks on moving lines.


A look back at the patrician attitude all prevalent in the DDR is provided in this direct translation from the original 1958 Simson Sport handbook. It states :
„The workers and engineers of the people’s own industry have by their combined work produced the Simson Sport.
This product of the vehicle industry of the German Democratic Republic is constructed to the latest technical standards. It is intended to help the owner in his professional work and to provide pleasure in leisure time. The longevity and reliability of a vehicle is dependent in the first place upon correct servicing and care. Instructions on how this is to done are given in the instructions for use.

Not a word of welcome, gratitude or congratulation on your purchase. Nothing at all from the point of view of the consumer. Why should there be. After all such considerations were exactly what the Soviet ideology detested most. And what a staggeringly deluded concept of state of the art motorcycle technology. Over in West Germany  NSU at Neckarsulm were racing the jewel like twin overhead cam twin cylinder motors that were within 1 year of becoming cloned by Honda when they photographed every tiny detail at the 1959 TT. In Italy Ducati were racing with desmodromic valvegear. And then there were the MV and Gilera fours not to forget to mention the Moto Guzzi V8.

What the general public in the DDR would probably have known little of was that Simson had developed its own double overhead camshaft 350cc twin cylinder racer with chain final drive.

350cc DOHC chain drive twin
350cc DOHC chain drive twin
250cc Chain drive single cylinder
250cc Chain drive single cylinder
AWO Enduro 350 cc
AWO Enduro 350 cc
The original Enduro team truck, a Barkas B 1000
The original Enduro team truck, a Barkas B 1000















Failed projects: 80cc single cylinder 2 stroke disc valve racer completed just in time for the 80cc class to be scrapped. Plans were afoot to turn it into a 125cc but then The Wall came down and it was never finished.

80cc 2 stroke disc valve racer
80cc 2 stroke disc valve racer
2 stroke with 4 stroke exhaust valve gear
2 stroke with 4 stroke exhaust valve gear








Some technical details of the Simson 425 Sport.

1958 Simson 425 Sport
1958 Simson 425 Sport as purchased

Capacity 247 cc
OHV 4 stroke
Single cylinder air cooled
2 valves , inlet tulip head 8 mm stem 36 mm head , exhaust conventional shape same dimensions
Valve springs 2 piece hair spring type
Valve guides phosphor bronze , inlet shorter than exhaust

Piston 3 rings with valve cut outs on crown
Bore and Stroke 68mm x 68mm
Compression ratio 7.2 : 1
Carburettor 26 mm diameter 15 degrees down draught flat slide
Air box sealed under seat delivering 28000 Litres at 80 kph
Output 14 PS at 6300 rpm
Top speed 110 kph
Weight 156 kg without fuel, tank capacity 16 litres
Fuel consumption 3.7 litres per 100 km
Tank range 350 – 400 km
Final drive shaft with rubber Cush drive
Gearbox 4 speed foot and hand change
Clutch single dry plate

Frame twin down tube with rear swinging arm
Front forks hydraulic single rate springs 150 mm travel
Rear suspension twin hydraulic shocks with pre load adjustment 100 mm travel
Footrests fully adjustable
Gear lever adjustable
Rear brake pedal adjustable
Wheels 3.25 x 18
Brakes full width alloy hubs 180 mm single leading shoe with ventilation ribs
Turning circle 3.5 metres
Ground clearance 145 mm
Electrics 6 volt 45/60 Watts via dynamo and contact breaker
Thankfully this machine has a 12 volt contact less power dynamo conversion
Illumination , park, dipped and main beam, rear brake light, headlamp shell mounted neutral and ignition lights

First look with seat and tank off
First look with seat and tank off
Inside tool box
Inside tool box








So what did the refurbishment of this machine entail ? Starting from the front the replacements have been :

Headlamp reflector
Spare ignition key
Long Bowden cable inner for clutch. The bike came with a slipping clutch. No wonder. The inner cable was too short thus the actuating arm fouled the bell housing at the rear of the crankcase so it could neither fully engage or release.

Pitted rusty headlamp reflector
Pitted rusty headlamp reflector
A clue was that the lever only came back this far to the bars!!!
A clue was that the lever only came back this far to the bars!!!








Actuating lever fouling the gearbox housing
Actuating lever fouling the gearbox housing
Bowden inner cable kit and nipples from e bay
Bowden inner cable kit and nipples from e bay








Fuel tap. This was a by product of the carburettor saga. More on this in a moment. A complete , refurbished ,original tap  has replaced the other original tap due to a horizontal fuel outlet which can accommodate the replacement carb.

Replacement refurbished original fuel tap with horizontal outlet
Replacement refurbished original fuel tap with horizontal outlet

Having wondered upon draining the tank why a cigarette sized filter sieve fell out a replacement was purchased. This had a brass sleeve which the loose one did not and would not fit through the tank entry hole. The original sleeve was still in the hole so was gently removed using a tap. The new filter then fitted in snugly and the new fuel tap went straight on.





Another issue when the machine was purchased was rich running, very sooty plug. Suspects were worn carburettor and or valve guides. Removal of the original flat slide carb revealed scored and worn slide so an after market 26mm replacement was bought.

Original BvF – Berliner Vergaser Fabrik carburettor – this attempt failed due to fuel not being able to defy gravity + fuel siphoning out of tickler breathing hole.

Original Berliner Vergaser Fabrik carburettor
Original Berliner Vergaser Fabrik carburettor
And the float bowl contained this!!
And the float bowl contained this!!








Replacement aftermarket carburettor – 1st one with breather hole in float bowl top – later replaced with 2nd.










The flange holes were too close together to fit on the cylinder head spigots. Cured with an 11 mm drill and round file. Tests with fuel on led to fuel pouring out of a tiny bleed hole on the float chamber cover joint. Tests of same thing with original carb did the same thing. The carb supplier sent over a complete new aftermarket carb this time with hole blanked off. No more leaks plus I now had 2 identical new carbs plus the old one. Bike still ran rich though.

Cylinder head. Very sooty exhaust valve area but clean on inlet side. Loose valve guides. Head sent complete to Norton Inter specialist Stu Rogers. New valves, springs and guides purchased. somehow ended up with mismatched valve and guides diameters. Stu turned new guides to match valves. Removal of existing valve gear revealed broken inlet valve spring, incorrect valves – both were tulip whereas only inlet should be –
plus both guides were of exhaust length whereas inlet is shorter. All this was corrected.

Piston crown after removal of soot
Piston crown after removal of soot

Off with his head – revealed this!







Cleaned up piston ready for head to go back on
Cleaned up piston ready for head to go back on

Head went back on like this







2 piece hairpin valve springs as removed from head – broken inlet spring is on the left
2 piece hairpin valve springs as removed from head – broken inlet spring is on the left









15-valves2 inlet valves, tulip shape, as removed + new guides, unfortunately wrong size as I ordered the wrong ones hence it was easier for Stu to make the correct ones.






Cylinder head with new valves and guides
Cylinder head with new valves and guides

Pushrods were mismatched. Inlet was bent alloy and exhaust steel. Both replaced with correct alloy rods.







New correct alloy pushrods
New correct alloy pushrods








Bike still ran rich.

Ignition. This machine has had a Czech made 12 volt power dynamo conversion fitted which does away with points.

18-12-Volt12 volt contactless conversion as first revealed showing Red timing dot incorrectly positioned, causing retarded ignition, it is now lined up correctly with the contact.

Timing with points fitted requires the crankshaft marker stamp of ZP Zundepunkt , ignition point, to be visible through the peep hole under a rubber bung in the  crankcase wall which is 10 degrees before top dead centre.


This peep hole reveals 2 stamped settings as flywheel is rotated. Here is ZP Zundepunkt – 10 degrees before further rotation reveals OTP Oberen Tot Punkt - TDC
This peep hole reveals 2 stamped settings as flywheel is rotated. Here is ZP Zundepunkt –
10 degrees before further rotation reveals OTP Oberen Tot Punkt – TDC

This peep hole reveals 2 stamped settings as flywheel is rotated. Here is ZP Zundepunkt – 10 degrees before further rotation reveals OTP Oberen Tot Punkt – TDC

Study of the power dynamo website revealed a vital missing page from the instruction sheets that came with the bike.

A tiny red dot on the dynamo must be set just before the static contact pick up when at ZP. The dynamo spins on the end of the crankshaft and is held in place by a left hand thread M7 35mm bolt. This came out with a nasty spongy feel. The red dot was miles out of place so the dynamo rotor needed to be removed and turned to the correct position. The special puller was purchased and rotor removed. Gentle retightening of the bolt led to that horrible sinking feeling as it turned more easily the tighter it should have become. Curses. Threads flatted on bolt and part stripped in 5mm wall of circular alloy bolt spigot. Replacement exact bolt obtained. No joy, same result. Through a chance contact an 8mm left hand 35mm Allen bolt was custom made plus loan of an 8mm left hand tap. Also purchased an 8mm helicoil kit and noticed that the drill size was not 8mm but slightly oversize to accommodate the helicoil insert. In a Damn the Torpedoes moment drilled out the thread using this drill and tapped the hole with left hand 8mm tap. Bolt went straight and tight. In a Take no Prisoners moment also purchase Loctite 270 with 44nM breakaway but decided not to use this for initial test runs in case the dot position was wrong. So rotor correctly positioned and bolted up tight. For the first time the motor did not feel like a two stroke gassing up due to too much oil in the mix. It had been gutless on inclines which led to too many revs and a broken rocker arm tip and dead bike. 2 complete rocker arms were located in Germany but with different locating holes diameters, 9mm and 11 mm. This bike needs 11mm so I now have not only 3 carbs but 3 rocker arms for one bike.

Possibly the largest collection of rocker bridges with rocker arms in the UK .........!!!
Possibly the largest collection of rocker bridges with rocker arms in the UK ………!!!

However bike still ran rich.
Fitted new HT lead, plug cap and plug. BSRR – bike still ran rich.
Removed carb bell mouth and connection to air box. BSRR.
Junked nasty original cheese grater air box cover so called filter and replaced with mesh.

Original air box cover and mesh – should have contained a filter but did not.
Original air box cover and mesh – should have contained a filter but did not.
Refurbished original air box cover and new carburettor
Refurbished original air box cover and new carburettor









A look inside the airbox
A look inside the airbox

Contacted carb supplier Adam Jahn who supplied 2 smaller diameter 0.93 and 0.82 mm needle jets. For first time ever the plug came out with no soot, still black on the outer electrode but deep brown on the centre electrode. Also the bike pulled as I had expected a 4 stroke single to do. The carb needle is at its lowest, weakest mixture notch, so a careful eye will be kept on carb colour in case it suddenly chalks up and risks the valves.




The original rear light Perspex inserts had been bodged together in the housing with nasty orange gasket goo. They are now properly in place with super glue. The feeble rear light was due to the use of a clear bulb. Replacement with red is comforting as modern traffic does not appreciate how slow this bike is. Side stand spring zip tied unobtrusively in place to stop it twanging off.
Footrest rubbers replaced with correct type.
Seat front mount holes in cover plugged and left unbolted to give rear swing opening access to air box and inlet trumpet.

All fuel hoses replaced.

Before tidy up
Before tidy up
Battery box wiring tidied up and secured + trickle charger socket wired in
Battery box wiring tidied up and secured + trickle charger socket wired in

Wiring contents of battery box untangled and zip tied out of the way.





26-battery box door

Push fit Battery lead terminals securely mounted
Solid state box securely attached to box lid with industrial Velcro
Trickle charger socket wired in
Battery box door lock retaining tab modified, courtesy of lump hammer and hacksaw, so that it now remains closed when underway rather than springing half open.
Replaced original glass 25 Amp fuse with modern spade type. I do not want to hit a pot hole and end up stranded due to a broken glass fuse.
Fitted complete new exhaust pipe and long cigar shaped silencer for that East German look.


And the silencer contained...nothing
And the silencer contained…nothing

The original pipe was dented and the silencer did not silence plus it rattled. Upon close examination, courtesy of the angle grinder cutting it in half, it was revealed that it only contained the end piece baffle and no other internals. It was welded back up together with the loose baffle firmly in place but it was LOUD and dented so it had to go.




Jobs to look forward to.
Replace toolbox lid lock with 16mm cabinet lock that will at least match the surviving lock on the battery box – decided against and left as is
Remove wheels and see what is inside brakes – done, all good
Clean and paint undersides of mudguards – done, all good
Clean and paint inside of tool and battery boxes inside rear wheel arch plus anything else under there – done all good
Still running rich – fitted Mikuni carburettor, problem solved at last !
Personally I do not care for over restored Christmas tree bauble bikes. I was in bike dealers, Redhill Motors in Brighton and Pride & Clarke in Brixton to name a couple and shows at Olympia and Earls Court as the 50s turned into the 60s and know that bikes did not look like that. The reasons are that 2 pack paint had not been invented plus modern preparation and chroming techniques had also not arrived. New bikes looked new but did not scream bling at you.
I think the patina of age is great which is why I have only touched in paintwork with Hammerite black gloss using water colour paint brushes.

One of my favourite details on the bike is the underside of the petrol tank. This model is the home market version as evidenced by the flat grey paint on the side of the tank. Export models had the wonder that is chrome. The underside of the tank speaks volumes for the Soviet era in which it was made. The spray was just flashed over and is unfinished at the centre, after all what did it matter under there ? I love it just like this.

What is it worth ?

After the reunification of Germany in 1990 all things ethnically German became highly prized and collectable. The Simson 425 Sport is exactly that. Today in this condition in Germany currently around Euros 6500.


February 2016 update

And, finally, after a chance encounter with Stromhardt Kraft of the Rennkollektiv Simson at the Ramsey Sprint in the Isle of Man in 2015 I undertook to coordinate bringing a team of Simson AWO 4 stroke racers to parade on the Isle of Man. 9 machines will parade on Sunday 28 August 2016 at Jurby and on The Mountain Course on Monday 29 August 2016 as part of the Classic TT Parade lap. But that is another story which will unfold in 2016 at the Festival of Motorcycling over the August Bank Holiday and which will be documented in another booklet.

Such was the gratitude for my help that no sooner had I mentioned the fact that my Simson 425 Sport runs out of puff on uphill climbs than a brand new oversize piston, rings, gudgeon pin and circlips together with a complete matching maximum overbore cylinder was sent over !

All this has now been installed and has transformed the performance. At last the bike pulls as you would expect a 4 stroke single to do and having dared, just the once so far, to give it full throttle I was amazed at how eager it is to rev.