Merkblätter zur Restaurierung der überschweren Kräder BMW R75 und Zündapp KS 750.


Herausgeber:  ERSATZTEIL    DIENST       Hans-Peter HOMMES       41748 Viersen Tiefenstraße 10

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Complaints in the Zündapp factory
connecting rod and bolts


H - P Hommes


© 2020 h-p hommes


Complaints in the Zündapp factory

The connecting rod bolts and connecting rods also caused some problems for the Zündapp works.

Complaint report from August 15th, 1942

There is a complaint here that in the customer service workshops alone, 15 of the first 1,000 KS 750s with engine damage had to be repaired.
Of these 15 pieces, 9 had suffered damage from the connecting rod bolt breaking off.
It is pointed out that only these 15 engines made it to the customer workshops.
However, a much larger number had to be repaired at the front or were scrapped directly.

Bergner's screws would tear off.
The Schaurte screws will not be affected until then.

Here, too, it was found that the cause can be found during assembly at the Zündapp factory.

The fitters of the engines tighten the connecting rod bolts as prescribed and secure them.
If the connecting rod cannot be turned easily on the crankshaft as required, the connecting rod screw is loosened by 1/6 and the fuse is loose.
This means that the connecting rod has air on the crankshaft from the outset and can hammer, which leads to the bolts breaking off.

Approx. 3,000 motors with 9 mm Bergner screws left the factory.
A high failure rate can therefore be expected.


Needle bearings that was yesterday

 The connecting rods today article 1007-1 are much more stable in construction, better in material and have high quality connecting rod bolts.

Then the connecting rod bolts were enlarged to 10 mm in the shaft.
However, this had the consequence that the connecting rod was weakened and there was now an increasing number of connecting rod breakages.
This also made the connecting rod so thin-walled at the countersink of the connecting rod bolts that during hardening it happens that the material is hardened through and thus tends to break even more quickly.

By this time, the Wehrmacht at the front had sent more than 50 reports of engine damage caused by a broken connecting rod.

Delivery of the Zündapp KS 750 to the Finnish Army in 1944
Here, too, several connecting rod bolts tore off in the Finnsh Army in 1944. 
The workshops were instructed to replace the connecting rod bolts on all engines.
Zündapp didn't really get the problem under control during the war.

In my workshop I keep seeing destroyed engine housings with severe internal damage caused by torn off connecting rods.
Most of the time, the tappet cup guides are struck, the center webs on the cylinder connection are knocked away and the oil pipes are bent or smashed at the bottom.
If the housing is not so badly damaged, such a housing can be used.




Technical information pages



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