Technical Information Pages for the Restoration of the BMW R75 and Zündapp KS 750.
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Oil Dilution -
© 2006 h-p hommes
Air Bubble Viscometer
Only few know this accessory. It is part of the winter equipment of the Wehrmacht vehicle.
With this device you can check the performed oil dilution of the engine oil.
At very high minus temperatures the oil is so viscous that you can hardly start the engine or not at all. Therefore a certain amount of gasoline was added to the engine oil.
When the vehicle should be taken out of operation the engine was stopped and it was checked with the air bubble viscometer how much gasoline was left in the engine oil after the last perfromed oil dilution. This is important to check because the lubrication of the oil decreases when the dilution is too excessive. Depending on the operation time and operating temperature an unknown amount of the added gasoline evaporates. The condition of the dilution of the engine oil is therefore checked with the air bubble viscometer.
For this purpose some oil was removed through the oil filler hole with a rubber hose. It was filled into the opening A of tube 1. The filling was only 2/3. Then the tube was closed.
|In tube 1 is the engine oil.
In tube 2 is oil with a 25% dilution.
In tube 3 is oil with a 15% dilution.
In tube 4 is the normal winter oil without dilution.
When you turn the unit by 180° the air bubbles start to rise to the top.
Example: Temperature of - 28°C.
When the air bubble of the engine oil is quicker than the one of tube 3 but slower than from tube 2 the engine oil is correctly diluted.
When the air bubble of the engine oil is quicker than the one of tube 4 but slower than from tube 3 you have to add gasline to the engine oil.
A. oil filler hole with closure B second opening with closure for better emptying.
Labeling of the device read from the top:
Orig. engine oil of the Wehrmacht undiluted
dito for prediluted to A
dito for prediluted to B
There is no labelling where the engine oil is filled in.
---transmission, rear wheel drive - sidecar drive are not diluted.---
Engine oil of the Wehrmacht (winter) corresponds to our SAE 30.
The grease of the bowden cables has to be diluted. We also experienced this during our winter trips in Norway at -30°. Those who did not have the correct lubricant on the bowden cables often went full throttle because the spring on the carburetor was too weak to withdraw the sticky cable. Better yet when installing the new bowden cables to lubricate them with a thin graphit grease.
-Winter label for the Wehrmachtsgespann-
with the data for the Zündapp KS 750. For the BMW R75 the data is the same.
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