Technical Information Pages for the Restoration of the Zündapp KS 750 and BMW R75
Monthly available on our website.
© 2012 h-p hommes
The valve gap is always set on a cold engine during the compression stroke.
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.
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
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