Technical Information Pages for the Restoration of the BMW R75 and Zündapp KS 750.


Herausgeber:  ERSATZTEIL- DIENST   Hans-Peter HOMMES       D-41748   VIERSEN   Tiefenstraße 10       Tel. 02162 - 8100933

Monthly available on our website.  



crown wheel - pinion bevel


H - P Hommes


© 2006 h-p hommes




I would like to talk about four additional points that must be considered in the restoration of the rear wheel drive.


1. Repair of the bearing seat of the rear wheel drive housing.

2. Checking of he inner and outer satellite gear housing.

3. Incorrectly hardened crown wheel and bevel pinion sets.

4. Loosening of the crown wheel - connection bolting. Causes and their possible consequences.


1. Repair of the bearing seat.

The interior housings of BMW and Zündapp are differently manufactured.

When the big bearing seat is worn out or damaged, then the bearing seat of a BMW housing can be machined larger and a ring can be inserted



The wall thickness of the Zündapp housing is weaker. When we machine the bearing seat lager and insert a ring then it can happen that the bearing seat is destroyed under strain. ( This happened to me).

So do not insert a ring in the Zündapp housing. You can reduce the bearing seat by welding and then machine it to the correct bearing size.


2. Satelite gear housing, also called cage.

The satellite gear housing (cage) consists of two parts. Many cages were destroyed by a broken off tooth of the crown wheel - bevel pinion set or the satellite gears.
In most cases this is indicated by the outer scratches on the cage.
If they exist we must assume that the cage already has major damage. 


Broken off gears got between the satellite gears and generated forces there that deformed the cage. 

Therefore check whether the out coming shafts are in one line and do not have no radial run-out.


When there are teeth or parts of teeth between the satellite gears the cage is often pressed apart and deformed.
The out coming shafts are not in one line any longer. The cage must be adjusted. 


Should this be the case you cannot just replace the two bushes for the shafts and then machine both in one line.

The center distance between the sun wheel and the satellite wheel would not be correct anymore and the next damage can be foreseen.

First the cage has to be adjusted accurately!



3. They can still be bought!

Cheaply reproduced crown wheel bevel pinion sets.
Improperly hardened and therefore breaking and then they cause a new expensive damage.


4. When you can axially move the connections of the rear wheel drive then the bolting is loose.



a.    The nut is not tightened enough.

b.    The nut is not a flanged nut and pushes only partly on the interior gearing of the connections.

c.     The gearing of the crown wheel and of the connections is worn out. Due to the rotation during the load changes the screw

        looses itsself again an again (nut locks do not help in this case).


Consequences: The bevel pinion moves towards the center of the crown wheel.

                           The position of the teeth changes and teeth or parts of them can break off.

                           The bevel pinion moves axially at the inside until it reaches the housing, small fragments come off the housing and they can then end up in bushings and teeth......





Instructions for adjusting the crown wheel bevel pinion set are available on the following page     Einstellblatt





We offer:

Spare parts + Accessories + Repair for Engines, Transmissions, etc. of 
Zündapp KS 750 and 600

We offer:

Spare parts + Accessories + Repair
of BMW R75 and Zündapp



H-P Hommes Ersatzteil-Dienst
Ersatzteile + Instandsetzungen
repairing + restoring

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