Technical Information Pages for the Restoration of the BMW R75 and Zündapp KS 750.
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H - P Hommes
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Engine - transmission suspension of the Zündapp KS 750
The engine of the KS 750 is kept in rubber bushings in the front engine cover.
The second bearing point of the engine - transmission - unit is at the bottom of the transmission.
There is a rubber plate between transmission and frame and another rubber plate between frame and the fixing plate which may only be preloaded to a predetermined extent with long nuts.
Thereby the engine vibrations are not directly transmitted to the frame.
A common mistake is to connect the transmission without rubber plates and without long nuts - only using normal nuts - with the frame.
Due to the transmitted vibrations vibration-fractures occur in different parts.
Attachment of the Zündapp KS 750 fuel tank
The fuel tank, second version, is rigidly connected with the frame. At one point on the saddle bracket and then again in the front with two screws without any rubber parts.
If you need to put a metal flap here, then only with a washer underneath.
When you put a rubber underneath the front attchament of the tank, the tank can vibrate creating a crack on the bottom flap which is attached beneath the under the saddle bracket.
This becomes noticeable by the tank loosing fuel.
The Cyclone Air cleaner KS 750
Here again some of our amateurs have the idea that the cyclone air cleaner is so heavy and should be strutted towards the frame.
The result is that the carburetor flange gets a vibration crack and breaks off.
The filter must be able to move freely. An attachment prevents this and leads to the breaking of the carburetor.
May be - before making a supposed improvement - be aware of the fact that at least 20 engineers in the Zündapp factory with years of experience have designed this construction as it is.
It can become quite expensive to go and change something as a layman without being able to foresee the real consequences.
The Co-Driver Seat Zündapp KS 750 and BMW R75
For many the small little lever at the right side of the co-driver seat is still not explainable.
The co-driver seat has a seat spring as spring element. Without a person on the co-driver seat, the extension spring is totally unstressed so that the seat support can freely move upwards and downwards.
This may destroy the bearings after some time.
That is why, when no passenger is on the co-driver seat, the seat is pressed down and the small lever is raised until the co-driver seat is locked and therfore prestressed.
Now when driving the seat cannot be damaged.
When a person sits on the co-driver seat, the weight of that person releases the lever and the seat suspension is automatically put back into function
Fuel Loss at Petrol Cap
First thing is that most of the fuel caps are rusty and therefore the rubber seal cannot seal properly. It helps a lot when we remove the rust at the filler neck with the help of a log of wood and glass paper until the surface is even.
Now we usually have a second problem.
The paint around the filler neck dissolves. However, mostly it is not the paint but the primer.
Now we have the layers paint: the paint, the primer and the interface. The fuel dissolves the primer more easily than the paint.
Therefore it makes sense to remove 5 - 7 mm of the paint and paint over the interface with two component clear varnish.
So the fuel can get no longer into the interface of the painting and dissolve them.
Schwingachse grease every week.
From 1943 there was no label anymore. First the fender was provided with an imprint for a short time, and then a transfer in white was applied in the factory and at the end only a stamp.
The stamp was delivered as a spare part until 1945 when the font of the stamp was no longer available.
So from mid 1943 onwards all BMW and Zündapp may not have a label but only a stamp or the transfer Order no. 3600-1.
BMW R75 Front Fork.
In the bottom of the rubber end pieces is a rubber element to cushion the connecting pipe.
In most spare part list this rubber element is not at all shown. But it can clearly be seen in the sectional drawing of the repair manual.
However, when the connecting pipe hits the rubber element, this is alredy destroyed after a few hits.
So please make sure that you have to put the hardend steel plate above the rubber element,
Order No. 2084-2
Spare parts + Accessories + Repair for Engines, Transmissions, etc. of
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