Zündapp KS 50 1972. Ref 1
Pictures from 2007 - 08
Text and pictures Björn Bellander
© Ref. 1
For this I first bought a Punch Monza and later a Zündapp for rally use. I decided that the Zündapp had to be one in good order. For a time I followed ads in local internet site Blocket. I found one KS50 1972 in Stockholm which looked very nice.
At this time I had no car trailer, but I knew a dealer who rented transporter cars for 1000:- a day. I had rented from him earlier. With this car in February 2007 I drove away to Stockholm. I knew that this moped was in good order and could be sold quite fast.
The owner was a car mechanic. He and his fellows owned a workshop behind St. Eriks Fair just outside Stockholm. After some trouble I found the place and got to see the nicest Zündapp I ever had seen.
I got in love at once and told myself that even if there were some no good things which could not be seen it was worth to buy. The price 18000:- Skr was of course to high so I offered him 16000:- Skr. I knew also that this kind renovation level had a price above this sum. Even if the engine that I could not examine was bad the moped was good enough for me. The offered price was taken at once.
When we rolled the moped out I asked him to start the engine. He succeeded to start it but the engine stopped after 20 seconds. This was in February and winter so I didn't found this curious. The moped was rolled into the car and a complicated tie up was done. I was in a hurry because I had 170 km back home and the rented car had to be redelivered.
During driving back to Virsbo let me have time to go through all thoughts that came up. Why didn't I asked more questions. I should have done a test drive. But I wanted this moped and didn't want to find anything that should cancel me from buying it. But as the pictures show the moped was inexcellent condition so why make trouble. All negative thoughts were thrown away and I heard myself saying "Well, well even if engine is bad I can buy a new one. I could never think that this almost happened later.
After coming home and a night rest. This one must be test driving. The carburator was a 17 mm and was equipped with an adjustable nozzle. After a long time of kicking and screwing I got it running. Anyway this moped was noticeable out of power. The engine did only run on high revs.
Note. Have mercy with my English
Study the enlargements from the two pictures of cylinder and piston below. Several so called moped experts who I talked to found this not so bad.
Well, what is now left to fix? The moped is equipped with electronic
contact breaker system and 12 V electricity. Might the breaker point be wrong?
I had not worked with this kind of system before. I had to consult the
net. It showed up that there were no god explanation of how to put it
right in an understandable way. Mostly it show up that the person
who is going to explain, not quite know the way or jump over some
point. It was even so that in one forum a so called expert wrote that no one
really know how to do. The theory is easy but in practice something
fully different. Now it is my turn to make a fool of myself.
The gearbox arm on the left side must be dismantled and also the 2 screws that are holding the cover. Take away the cover. You don't need to dismantle the kick pedal. In the rear there is a rubber tightening. Probably most old moped have lost it. But if it is still left, wrap it off with a screw screw driver and lift it off from it's position. Put some oil on the driver before. Then take away the cover. Look at the next picture. Now you can see the balance wheel.
Inside it you find the ignition system. Your work is now to make marks on this wheel corresponding to the crankcase so it will be easy to fix ignition next time. Now this is not done so we must continue our work. Next task is to dismantle the balance wheel. First you have to loose the center nut. In order to do this you must keep the crankshaft locked. Use as a suggestion my way with a bent flat ion. See picture.
Take a box spanner an take away the center nut. Then you have the problem to take away the balance wheel from it's place on the conical axel. For this you must buy a tool. This tool all moped owners must keep in their tool box. See picture. It will pull the balance wheel of the crankshaft. Take care of the woodruff wedge. The top head is already dismantled. All this work to take away the balance wheel is only for to control the
fastener which hold it in place are ok. It can be hard to adjust later with the balance wheel mounted. Study the coils and note that one of them is covered with black isolation band. This one corresponds in line over the wedge, on upper side, to the piston in top position. 180°. This is only a thing you can notice. To continue mount the balance wheel. Now there are 2 ways of position the cylinder in top. With a sliding caliper or a micrometer tool mounted in spark plug hole. This one is expensive so we work with sliding caliper. Measure with help of the
Look at the picture. Now mount the cover and start the engine. While engine is running take away the cover straight out. Take a car battery mount the ignition lamp according to picture. Run the engine and control that your ignition mark show up in the right place with help of the lamp. If not , dismantle and turn the coil plate. Test again. Do this till everything is alright.
If the engine still is not running good the carburator is the next troublemaker.
carburattor could possibly be ultimate. I searched this kind at several markets but could not find any. The types that would be found was 9.5 and 17 u-boat types and all was in a miserable condition. Then I learned that Bing had only produced 9.5 and 17 u-boat types. With this problem time went on till next year when I ordered a 12 mm at Cycle and Sport in Grängesberg. Don't ever think that it was just
like to mount. It had an unmarked jet and that the fuel bowl position was depending on carburator mount position. This last thing was not a serious matter. Of course the connections didn't fit. I had to turn a fitting. See picture. Additionally I had to scrap an old 9.5 in order to use back part. This was cut off and mounted on the new carburator. See picture. It did fit perfect and was hold in place by hand pressure fit. Now I had to find the
right setting up. Now I had to find the right setting up. After testing I found that the needle should be positioned in the second mark from upside. But the engine would not rev up. This is caused by that the jet is too small. I bought in a market jets. The small part according to picture. I also bought steel drills in a special shop with diameter 0.30 to over 1 mm in steps of 0.05.
Last picture show the Bing 12 mounted including the changes I did. The moped can now do as best 40 km/h and has much better power. It is still sensible on gas position.
Here I show how an original system looks like for my Zündapp. For me there were too small holes for the exhaust. This was only in my believe because I am used to V8 cars exhaust. Mopeds with 2 stroke engines must have a certain volume and resistance to run good. Straight pipes in a 2 stroke motor is worthless.
The result of all this was that I went back to the original 17 mm Bing carburettor. Read more in "What happened later".
Another thing is that you must meet up to an examiner man which is allowed as an authority. In my case it was Kent at Lisjö Krom. A well known MC man. It is best to go there on a Saturday or Sunday in the morning. Of course you phone him first. In this case your visit will not interfere with his chroming job. These pictures show Kent controlling our mopeds and filling up the form. Then it is just to send to Stockholm and wait. Normally you will be approved.
Zündapp KS50. Ref 1
tell you how to dismantle engine still in frame.
Text and pictures Björn Bellander
Cross view of engine. Ref 1
This part is for all who want to follow a full dismantling of engine.
Normally to dismantle the engine you must unscrew it from the frame and
put it on your work bench. It has nothing to do with exchange of parts.
I did it only for the main reason to control that everything was ok. It
is better to do the control in the beginning than dealing with eventual
hidden faults later.
Start to take away the covers on left side. Next is to take away the lock nut for chain driving pinion. To do this now is good because you can lock it from turning with help of gearbox and rear wheel. If not good for you do as the picture show. Lift of the chain.
Now it is time to empty the oil from gearbox (hexagon screw), then loosen all screws in the clutch house. There are 8 screws. They are put both from left and right side. The nut you see among the 8 screws is the one that hold the clutch movement in the position. Normally you don't need to take it away.
Now start to dismantle the clutch. Are you clever do as I show in the picture by pressing the clutch springs together. This is a good way because otherwise it is easy to destroy the small nuts and threads. Now, note that these nut are screwed to the bottom of the
We have now dismantled all what I think are good except cylinder and piston. This is simple. Away with exhaust pipe and then 4 nuts which hold the cylinder head. Now you can take away
the head. Pull apart the cylinder gently. Bring a finger under the cylinder when it comes off
crankcase hollow. For security fill the crankcase hole with paper. This is 95% security. Of course you can snap away a ring on your floor and never find it until months later. Tap then the piston pin out with a rubber mallet and a drift pin. Bring 2 finger under the piston to take the needle roller bearing that may fall down. Have a wooden piece as a holding on between connecting rood and stud bolts.
Now we are ready so far. Next work is to bring the remaining engine parts of the frame and lift it up on your bench. This of course if it is needed.
It may be nice for your knees to stand up and take a rest. You can also pour up some coffee and get thought about what's has been done. Remember also that it is extremely important to have good control of all pieces, nuts and screws. Then go inside your home, kiss wife/girl/friend and go to bed. You have not strength for more.
Start with work next day after a good nights sleep.
The crankcase halves including gearbox. Ref 1
tell you how to continue dismantling engine on your workbench.
Text and pictures Björn Bellander
Cross view of engine. Ref 1
getting hard to explain through text, so my pictures must show most of it.
First you can see that the halves are on the way to be split. It is good to have a hole in your bench where you put crankshaft end. Otherwise it will be unstable. Turn the engine so that the clutch side is against the bench.
Furthermore they are mounted with hand pressure fit. That's the way I use the foursticks in order to gentle get the two halves apart.
Well this was the whole engine in part. Of course you have put all nuts, washers screws and gear and axles in different plastic bags with a note on. If you have taken pictures, it is also good. You have also, of course a set of gaskets among your reserve parts. Perhaps you must do something about the engine, or only curious. Good advice are anyway to change all bearings, tightening and gaskets. Make anyway a good look at the clutch plates.
Zündapp KS50. Ref 1
happened later 1.
Text and pictures Björn Bellander
Engine equipped with "Sunfeather" cylinder. Ref 1
Life isn't easy, people will never be satisfied. Even if my moped now
acted normally, I had the feeling that it was no power in it. After
several km of driving I became more and more disappointed. Anyway I read
in a forum that this moped with original Swedish cylinder was a
very dull one.
At last I couldn't resist the temptation or in other words my soul would never be satisfied. This ghost who is placed in a good place to be able to push my thinking. At last I put myself in front of the ghost that means in front of a mirror and asked myself, the ghost mirror figure: "Do you think that I should buy a nice trim cylinder so I can get better power and speed for this bad moped?" and of course my ghost mirror answered: "Naturally, you are worth it after so much work with that nasty engine."
When I got this stuff home I almost got a chock to see the piston design and also the inlet port of the cylinder. The piston ring had the latest design and was place high up. Now I understood that this must be good.
I quickly mounted piston and cylinder, but the exhaust pipe I had some work with, because the connection of the pipe had a little thicker edge. This must be ground away. When this was done everything did fit very good with the help of a rubber hammer. Round this place I put a good bracket just a little more expensive. I must also move the return spring of the moped to the left side. Otherwise there were no more problems.
For the carburetor it became a remounting of the old honest 17 Bing. In this I put after testing first main needle 2.20 and then found that 2.12 was best. I cannot find any needle with that figure in the catalogue. Lucky enough this 2.12 followed originally with the moped when I bought it. The throttle needle was mounted in second groove. The adjustable needle was opened 3/4 of a circle. The chain pinion I chose was 13. In the rear I didn't changed.
All this became super and the moped has good power and can rev more than I dare. But I just wonder why I must drive carefully for 1000 km before allowed to press the engine. It is a long range for a moped. Next time when I lift off the cylinder, I will take photos of the inlet hole.
Now everything feels fine.
20110412 this moped was sold to a boy in Gunnarskog. Hope it was the right moped for him.
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Referece 1: © Björn Bellander bjorn.bellander(at)telia.com
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