Zündapp KS50. English version.

My KS50 in front of garage. Ref 1

View over speedometer. Ref 1

Engine view. Ref 1

Front wheel. Ref 1

Rear wheel. Ref 1

It is nowadays popular with mopeds, and I needed one for local use to the food store and shorter trips around Virsbo. I wanted also to participate in moped rallies.

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.

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Ad in Blocket paper. Ref 1

This was the ad I fall in love with. My knowledge about mopeds were and are still not so impressing. Many persons who has activities with MC and mopeds has had this as an interest for up 30 to 50 years, while I have only the elementary knowledge that makes an engine function. I bought a bike 1981. It was a new Kawasaki 400. This kind was not for making my own service. After this I had a Yamaha 750 and a BMW 900. I was not at least worried about making service on this Zündapp because earlier I had bought an old Puch Monza and a Zündapp is just the same to make ready.
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.

Receipt for transport car. Ref 1

Receipt for the moped. Ref 1

I went away on some test runs and made the observation that the engine became more an more out of power and demanded higher revs in order to run. Well, well it is just as always I must control most things in the engine. This was the start to dismantle the engine.

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Note. Have mercy with my English

Cylinder part. Ref 1

I had my suspicious thoughts. But from the beginning one always lift the top head and the the cylinder. This was done and the discoveries started to come up to my knowledge. The cylinder had in in the hands of some former owner seized and got long scratches. Piston rings were also destroyed. By this the engine had bad compression and because of soot even more bad compression. The piston ring was just as it was glued in its place.

The scratched piston and piston ring. Ref 1

The schratched cylinder hole. Ref 1

All compression went down in the base chamber.
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.

Part supplier. Ref 1

The first I did was to call KJ TOOL. I was informed about this moped spare seller. I asked for a new cylinder with piston and ring. Later I learned that there are different diameter pistons and that there were engines with different cylinder strokes. Long stroke from 1971. The last question KJ solved for me and about the different diameter it was no idea to explain. I got a standard piston. This piston was now mounted in the engine. But it was no good function until it lost its power again.

The old,scratched one, cylinder inlet trim. Ref 1

The new more moderate pear cylinder inlet trim. Ref 1

The new exhaust pear original pear cylinder. Ref 1

The new original pear cylinder marking. SVE. Ref 1

The cylinder marked with SVE. Ref 1

After another new mounting I found that the piston ring was "glued" in place again. I realized that the cause must be the bad cylinder. But getting a new pear cylinder was not so easy. KJ could not fix one. So I went to local internet ads where I found a new German one in original parcel for 1595:-. I paid it and my new cylinder was delivered by post. Now I could compare them. See pictures. The old one had an impressive porting. I had bought several gaskets from KJ so I had no problems with that. In order to change things on a moped are no time consuming comparing to an American Cadillac. A moped takes one hour and the Cadillac can take a week. Of course you must do things right. Well put on the new cylinder. A long time screwing on the carburator to get the engine running good. My moped was anyway annoying less of power at start and in smaller road hill climbing. My Puch Monza went much better. After some time of driving the cylinder was dismantled again and the piston ring was firm in place. Oh my Good as they say in America. What is this. Now my thoughts came to that it must be the wrong diameter. I measured the cylinder diameter carefully and called KJ and ordered three different pistons. I mounted the one that gave me 0.04 mm play. With this I drove 2 rallies. But when the last helping man in the rally drove up and asked if it was something wrong with my Zündapp I realized that my speed was to low. At straights my max speed was 30 km/h and on road hills it was 20 and I had to put in 2 gear. Extremely dull. Now I could not blame the cylinder.

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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.

Remove the gear changer and unscrew 2 screws. Ref 1

Lift off the cover and you see this. Ref 1

This is one way to screw off the flywheel nut. Ref 1

First some pictures of the parts we have to handle.
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

The rest of the ignition system. The al. part is the voltage regulator. Ref 1

Ignition system. Ref 1

Puller for the flywheel. Ref 1

ignition system and that 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

How to check ignition with a timing lamp. Ref 1

Marking the flywheel. First is ignition advance, second is TDC. Ref 1

caliper as exactly you can from the top plane of cylinder to the top of piston. Now you have found TDC. Read what the caliper shows and ad 1.7 - 2.0 mm. The ignition point is 1.8 to 2.0 before top. Turn the crankshaft backwards to this position with help of the sliding caliper. There is an arrow on balance wheel. Make a mark on the radius surface against an edge on the crankcase. Now you have 2 marks TDC and ignition point.

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.

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Bing 17 mm. Ref 1

Outlet adapter for Bing 12. Ref 1

Switching over backside adapter from old Bing. Ref 1

Needle and jet dismantled. Ref 1

This moped was equipped with a 17 mm Bing carburator with adjustable nozzle. This combination gave me several problems. One thing, I could not get the right nozzle point. Further this as I mentioned earlier that the piston ring glued together with the piston and lost its tension. I tried to mount a 9.5 mm carburator but this combination acted like a plug and the moped was even worse. I realized that a 12 mm

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.

Mounting with a cage tool. Ref 1

Bing 12 ready for start. Ref 1

Now I had everything to try out the right nozzle. I started to drill 0.40 and found out that 0.65 was best.
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.

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Kent, the examination man, gives himself an overview of the moped. sig en överblick av mopeden. Here it is a Chappy. Ref 1

...filling up the paper. Ref 1

You can get an veteran insurance for a moped 20 years old or more Through the Swedish MHRF insurance. This means a much lower cost than normal. You must be a member of course. In my case I am a member of MCHK Mälardalen. You must deliver at least 5 good photos. Fill in a form which you can fetch from MCHK on internet.

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.

... checking the engine number. Ref 1

...and signing for approval. Ref 1

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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.

Left cover. Ref 1

Preparing to take away the flywheel. Ref 1

If in trouble you can do like this to remove chain gear nut. Ref 1

If you by some reason are going to dismantle the engine you can do it in 2 ways. Take away as much you can when it is still mounted in the frame or primary unscrew it from the frame and make everything on the working bench. The experienced mechanic of course make in the latter way. The advantage to make in the frame is that you go step by step and learn in a better way how it is screwed together. First a picture of the cover from left side or kick side. It is turned so you see it from inside. Next picture shows what it covers. The splitting of the engine must always be done on the bench.
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.

As before removing the flywheel. Ref 1

Tool for bringing the flywheel off. Ref 1

Coil plate and checking if there is any close marking. Ref 1

Rest of the ignition system. Al. part is voltage regulator. Ref 1

Next is to loose the flywheel and ignition system. Start to loose the center nut for flywheel. Look at my picture how to lock it. Then you can dismantle it with a tool like that in next picture. It is a puller you must buy. Good to have for the future. Control if there is a mark on the coil plate for the exact position of ignition. If not make it before taken away. The coils is mounted on a plate and this is locked by

Now all ignition parts are away. Ref. 1

Start here on the right side. Ref 1

Backside of the coil plate. Ref 1

screws in three oblong holes. Hang up the coil plate in a good place of the frame. Be careful with the threads for the plate. There are 2 M5 and not so long threads. Here it is a good idea to mount strengthened threads to get rid of future problems. Well away with the coil plate. On the picture you see the back side and how it look like inside. Now let's go over to the right side. First loosen the rear cover and take away the bearing part for gearbox main

Gearbox main axle bearing on right side. With this you put the gearbox axle play. Ref 1

Main cover on left side. Ref 1

The crankcase screws which are taken away. Ref 1

axle on the right side. The part that is fastened with two small screws, first picture, keeps the main gear axle in the right position against second axle. Screw it away. When remounting. First engage second gear and press in the axle to the left. Screw the special one with the 4 notches so it just reach the bottom without changing the position of the axle. Now draw this "notched screw" with the axle back to the right. Now wind it back while counting the amount of quarters to the bottom again, without changing the position of the axle. Perhaps you have counted 12 quarters. Now wind it back half this quarter amount and then lock it with the two small screws and its special washers. Now the axle in situated in the right position. The long screw in first picture is for another purpose.
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.

The clutch cover on the way to be taken away. Ref 1

Inside the clutch cover. Ref 1

Gear changer. Ref 1

Study the inside of the cover to understand how the clutch works. Take a rubber mallet and hit gently to make the cover loose. Now it pour some rest oil so have a small vessel under to bring it up. Other wise use toilet paper. If not earlier you now see that the brake pedal must be removed before this. Sorry. The second picture is what's inside. In the middle of the clutch plate you see the release pin for the clutch. Take it out. Note also the main gears from the crankshaft. Look just to the left of the clutch. There is on piece that has fallen down. Don't worry

This is the way to tighten the clutch springs. Ref 1

Dismantle the clutch house. Ref 1

Clutch disk unit. Ref 1

this is normal. The part hangs on a dowel in the cover and is a bit tricky to mount. It has to be mounted in a guide wedge on the gearbox axle. Spare that trouble for later solving. Note also the large gear reduction between crankshaft gear and clutch gear.

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

Clutch housing without disks. Ref 1

Clutch disks on the bench. Ref 1

treads. You will never need to ask how hard they nuts must be mounted. This is also good because there will be the same pressure on all springs when remounted. Now it look like this.
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

The parts of the piston. Needle cage, piston pin and locking needlesar. The needle cage is not shown. Ref 1

Dismantling of piston. Ref 1

just to save the piston to fall against any hard edge. Of course you have a suitable seeger ring tool in order to take away the stop rings. It is almost a must. Otherwise you risk to drop at least one ring inside the
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

Here I tell you how to continue dismantling engine on your workbench.
Text and pictures Björn Bellander

Cross view of engine. Ref 1

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Unscrewing of the last screws ignition side. Ref 1

Unscrewing of screw clutch side. Ref 1

Now you have to localize the left of the screws that hold the crankcase halves together. Note that I on the picture have removed the small main gear from the crank axle. It has a nice construction containing one bearing ball instead of a woodruff wedge. Note also that the clutch housing still is in place. You cannot take away it until you have split the engine halves.

On the way to split the halves. Ref 1

Left crankcase part when lifted off. Ref 1

Wooden sticks to bend the halves loose from each other. Ref 1

Now it is
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.

Getting the gearbox axle free. Ref 1

Showing the seeger ring for clutch housing snaped off. Ref 1

Showing the seeger ring for clutch housing snapped off. Ref 1

What's left of right side. Ref 1

As you can see on the picture there are several axles coming out of the halves.

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.

Clutch axle off and the seeger ring still in place. Ref 1

The last axle pulled off and showing the distance washer. Ref 1

The right part look like this. On your bench it is the lower part. Be very accurate to note all distance washers where they are placed. All are different. You are now in the position that different things can be made. My opinion is to first dismantle the main clutch wheel. It is locked by a seeger ring behind the gearbox axle. The axle close to crank shaft axle. First lift up the middle axle. The short one. Just pull it upwards. Then you can pull up the clutch axle. The one nearest crankshaft. Now you see the seeger ring which keep the main clutch wheel in place. Now pull up the last axle before you turn the clutch cover in order to lift the clutch wheel away. It is mounted with a light press fit in the ball bearing. You can now hit the remaining 2 axles ends wit a rubber mallet, clutch house end crankshaft. This can be done with a rubber mallet.

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.

GOOD LUCK!

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