The Historical and Technical Development of the Zündapp KS 750

H-P Hommes

The Zündapp KS 750 is a bike with sidecar which was developed for military use. Only military demands were considered on how to build it. The economical aspect of the production was less considered.

It was necessary to build the best bike, suitable for all situations, with a high loading capacity and a maximum of reliability.

Only this way a technically perfect bike with sidecar drive could be built where the costs were only second rate. Later on two VW-Kübelwagen could be produced for the same amount of material and work.

In the thirties many bikes were delivered from Zündapp to the Reichswehr.

All these bikes, especially the K 500, KS 600 and K 800 had a decisive disadvantage. They were only slightly changed civil versions, that did not meet the military demands.

Already at the end of 1937 the Army Arm Department in Berlin demanded the development of a bike with the following criteria:

The bike should have a payload of 500 kg , which corresponds to three soldiers with arms, ammunition and full equipment .

The bike should have fully loaded, a permanent speed of 80 Km/h on the Autobahn and 95 Km/h maximum speed. The minimum speed had to be 4 Km/h to accompany the marching troops.

For tyres 4,5 x 16 `` cross country tyres should be used.

The minimum ground clearance had to be 150 mm and clearance under the mudguards had to provide for the possibility to put on snow chains.

First of all Zündapp thought to modify the Zündapp KS 600 in such a way to meet the demands.

But the constructors recognised very quickly that the KS 600 was not suitable for further development. Chassis, engine, transmission, front fork and many other parts would have to be reinforced. Zündapp recognised that a only a new construction of the whole bike would lead to the desired aim.

Therefore they started to develop a new homogeneous bike and had two prototypes at their disposal in 1939, which the OKH used for test drives.

In both bikes the cubic capacity was increased to 700 ccm and the cylinders were lifted at each side by 5° to obtain more ground clearance. Though the cubic capacity was later further increased to 751 ccm.

BMW also received the order to develop a similar bike. After long test drives with the BMW and Zündapp prototypes the Arms Checking Department was convinced that the Zündapp KS 750 was far superior to the BMW R 75. BMW was asked to built the Zündapp KS 750 under licence.

Zündapp agreed happily as it appeared their competitor BMW was not able to build a bike to of the same standard. Understandably, BMW refused to construct the Zündapp KS 750 under licence. However, the OKH asked BMW to take over the superior characteristics of the Zündapp KS 750 such as rear wheel drive, hydraulic brake system and wheels.

BMW and Zündapp also agreed, as demanded from the OKH, a standardisation of many building parts to make the spare parts deliveries easier.

Until 1940 the development continued. Then seven bikes were used for longer test drives. At its end in April 1940 the OKH confirmed full Army acceptance of the Zündapp KS 750.

In spring 1941 the production of the Zündapp KS 750 started.

Production quantity 1939 2 units (pre-series) Chassis -Number

1940 7 units 600 000 - 600 006

1941 288 units 600 007 - 600 295

1942 7.228 units 600 296 - 607 523

1943 7.131 units 607 524 - 614 654

1944 3.515 units 614 655 - 618 169

1945 115 units 618 170 - 618 284

1946 205 units 620 001 -

1947 76 units

1948 68 units 620 349

In eight years 18.695 Zündapp KS 750 were built in Nuremberg.

The_Zündapp_KS_750_received_in_its_final_version a closed oval tube chassis that was so rigid that it withstood all strains. The sidecar was fixed to the rear wheel drive with a central connection. The rear wheel drive gives 70% of its energy on the rear wheel and only 30 % on the sidecar wheel.

This gives the bike a good straight driving condition. With a lock lever the rear wheel drive can be locked. But this should only be done when the wheel is on loose ground and spins. Anyone who tries to drive with the lock will immediately recognise that the steering function is reduced.

For the first time a bike was equipped with a hydraulic brake system as standard. During the construction the asymmetric energies of the bike were considered. The rear wheel got a 22 mm wheel brake cylinder, the side car only a 19 mm wheel brake cylinder. This achieves good balanced braking.

The_transmission is not a chain transmission as the one for the Zündapp KS 600, but consists of straight cut cogs. This causes the Zündapp-typical roaring. When a bike comes towards you that sounds like a streetcar, it can only be a Zündapp KS 750.

The transmission has four gears, four cross country gears and four reverse gears as well.

You can only switch the cross country and reverse gears into the first gear. They have a lock in the gear shifting gate. The transmission is an easily comprehensible construction also easily understandable for the layman. In contrast to the BMW R 75-transmission it is more solid, gives an audible sound while shifting without being hurt, and has a long life span.

The engine was increased to 751 ccm, by changing the stroke level to 85 mm. The valve gear and the cylinder heads are identical with the Zündapp KS 600. The cylinder heads of the KS 750 have four cooling ribs below, the ones of the KS 600 only three. The KS 600-head cannot be fixed to a KS 750-engine without changes. Because the cylinders were changed to 170 ° V-engine the guide drill holes of the bumpers are in a different angle. For the KS 750 they also did without the modern battery-ignition in favour of the electricity-independent magneto ignition.

A magneto ignition from Noris and partly Bosch was fixed.

The Bosch-magneto ignition needs far less maintenance and is more solid than the delicate Noris-magneto. Both magneto ignitions were equipped with an automatic ignition control.

In front on the crankshaft sits a 6 Volt 50 Watt generator from Noris. A Solex Typ 30 BFRH Carburetor was fixed. A proven product mounted in many cars before and after the war. But the description does not tell you jet size of the carburetor. Therefore not every BFRH 30 is suitable for a Zündapp KS 750. To start the cold engine more easily the carburetor is equipped with a cold start system which is turned on with a lever on the engine cover.

Until mid of 1942 the bikes were delivered to the army in the colour Dark grey RAL 7021 .

The Luftwaffe received their Zündapp KS 750 in the colour Black grey RAL 7019.

For the Deutsch Afrika Korp the bikes were delivered in 1941 -42 in Africa-Beige RAL 8000 .

From 1943 all army vehicles were painted in a Dark yellow - without RAL No.

In the first two years when the Zündapp KS 750 got into production the Army asked Zündapp for some more alterations_and improvements.

Zündapp reacted promptly and improved the first version in several points. Only the most important changes are mentioned hereafter.

First of all the steering damper was changed and replaced by one that could be regulated with a hand wheel.

The fork girders were prolonged 10 mm to have more space in the mudguards.

The tank received a better fixing and the tool box cover was positioned on the other side.

The knee protector rubbers were omitted.

But a real problem was the carburetor freezing and the insufficient effect of the wet air filter. Zündapp remedied the matter by fixing a Neumann-centrifugal_air_cleaner_with_preheating. In a letter to the Army repairing workshop, Zündapp asked them to exchange the existing wet air clean filter and offered cost free replacement.

Because of the necessity to save of material 1943 a number of building parts were produced in less expensive materials.

The cylinder head covers were no longer produced in light metal but in sheet metal.

Also the housing parts of the rear wheel and sidecar wheel drive, the hand lever and the brake shoes were produced in less expensive materials.

The Zündapp KS 750 had the sidecar in two versions.

On the one hand the Zündapp-own sidecar type 40 - or in short the BW_40 - , a very modern sidecar chassis produced from Zündapp. The sidecar wheel is equipped with an adjustable torsion bar suspension. The boat has also a torsion bar spring. This gives the sidecar chassis a smaller building width and the care-intensive oily leaf springs can be omitted. This way of construction was far more lavish than the more often used BW 43 from Steib, Nuremberg, But was fixed to the Zündapp KS 750 in lower quantities.

Zündapp produced the BW 40 themselves. From 1943 the BW 43 was produced for KS 750. It was a more simple sidecar construction. The sidecar wheel fitted with suspension over the swing housing with an inside tube spring . The boat hung on two outside leaf springs.

Zündapp BW 40 chassis with Steib boat W.Krad B2

The_boat_type_“W.Krad_B_2“ was delivered from Steib. It is a better version of the type “W.Krad B 1“ which was fixed to the Zündapp-models KS 500-600, K 800 as well as to the BMW bikes BMW R 12 and R 71.

You could especially recognise the B 2-boat, because it had above the back-rest on the right and left hand side gusset plates for reinforcement and a bigger back tunnel opening, to give space for the thicker BW 40-sidecar tube. The seats in the boat were covered with black synthetic material and the back-rest had gaps at the sides so that there was space for the holsters. The covering was made of canvas in beige or blue-grey depending on the bike painting.

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