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

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

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Valve Gap

The valve gap is always set on a cold engine during the compression stroke.   The engine is turned on top dead centre.   The cylinder, which is adjusted, has both valves closed.   at the other cylinder the rocker arms are set on overlapping.   The valve gap is measured between the rocker arm half ball and the valve end.   The valve gap must be at least 0,25 mm (0,01 inch).   When driving in hot climates the Wehrmacht required a valve gap of 0,30 mm.

To adjust the valves too tight, which means that the feeler gauge goes only through with difficulties, may reduce the valve noises but can also lead to the burning of the valves.
 

Remember, when the engine is really hot all materials will expand also the push rods.
When these expand more than the cylinders and everything else which belongs to it, the valve gap reduces itself.
 

This can go so far that no valve gap is left at all.
Does the rod then expand a bit more, the valve remains open and the hot exhaust gases press themselves through the small gap during the explosion stroke. 
Then the whole thing is really overheated and within no time at all the valve is burnt.

The valve gap on an engine with high operating temperature is only 0,05 -0,10 mm.

This can even happen when you have installed push rods from the wrong material.
This applies for the Zündapp KS 750 as well as the BMW R75.

Measured on a cold engine the valve gap always shows the set 0,25 mm an.

But when a high operating temperature is reached the valves remain open and burn up.

Now you are looking where the problem is, and everything is renewed that has been damaged.

But naturally the push rods are not replaced.

You have just bought them reasonably priced, they really look like new and were not at all damaged.
 

Lucky you.

Or not!

Because may be they are the cause of your engine problems.

Good push rods of the right material you can get from us.

For Zündapp KS 750  order no. 1022

For BMW R75 order no. 2027

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

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Ersatzteile + Instandsetzungen
repairing + restoring

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