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


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

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 © 2013 h-p hommes




There are still people who pay a lot of money for original pistons. I do not.
The piston technology of the 30s is generations back and that in all respects.
Neither type of construction nor material is comparable to today's piston.

Today's pistons are made of a special material and are not simply cast from light metal. They have a deaxially arranged piston pin, cast-in steel rings and special oil scraper rings and compression rings. The lower ring - as normal at the BMW R75 - has long disappeared as unnecessary.
It is therefore somewhat surprising that some one always comes up with the idea to recreate piston in a primitive way.


It is amazing what people come up with. We were offered such a replica. At first glance it looks like the original piston of a BMW R75.
We looked at it closer and  realized that it was cast in a topflight light metal.
Without a deaxial piston pin, without steel rings inside and with extremely wide piston rings.
There is a lot of friction with wide piston rings.
For this, the bars between the rings are kept pretty narrow.
A great design, but I do not want to install it.


Our pistons were especially produced for our company  in a large piston company that produces pistons for cars and motorcycles and also the piston rings are a quality product (Made in Germany) and not made of cast steel.

A special treat gave me a discussion about pistons at a meeting in Brisighella.

Zündapp driver:
Your Zündapp is really doing well going up the mountain. I could not tag along. Do you also have the 30 hp Tatra pistons?

----Me: No what kind of pistons do your mean?

Zündapp driver:
They have 30 HP. I got them mounted from somebody (forgot the name though).

Do they have different dimensions, higher compression or something?

Zündapp driver:
No no ist is all like original. But they perform 30 HP!

And the earth is a disk, you believe it when you have been told only long enough

Oh, what should we talk until we are blue in the face. Everyone wants to make his own experience and life experience costs sometimes. One also has the advantage that one gets to know one's bike better and better by frequently changing parts. Whether one likes it therefore also more, I can not say.


The pistons manufactured by us today are the same as the ones used in car engines today, eccentric pistons

Here is a short scheme to mount them properly.

Memory hook: Rechts ist die Schrift lesbar =  Richtig ( to the right the writing is readable = correct)

If you would fold up the pistons, as in an in-line-engine, then the writing of both pistons shows to the same side (right)

verything clear?


Zündapp KS 750 We have the good pistons! in the dimensions 75,0 mm, 75,5 mm and 76,0 mm (für sleeve bearing connecting rods)

BMW R75          In the dimensions 77,0 mm 77,5mm 78,0 mm 78,5 mm 79,0 mm ( Our new cylinders start with 77,0 mm)


We offer:

spare parts + accessories + repair for engine, transmission, etc. of the
Zündapp KS 750 and 600

We offer:

spare parts + accessories + repair for the

BMW R75 and Zündapp


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

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