Thanks Rocky, Rene and Doug for your replies.
The clearance of the 2nd gear cone against the 1st gear snychro was also way too small (approx. 0.2 mm). Hence, wear must have mainly occured on the cone, not the synchron ring.
I have my gearbox at a racing gearbox manufacturer. They also service gearboxes for historic race cars:
We also discussed to use undersize synchron rings to compensate for the worn cone clutches. I liked this solution for its simplicity. However, Christoph, the mechanic in charge convinced me that ZF did use sinter steel synchron rings for good reason and they would last much longer.
Meanwhile, I separated 2nd and 3rd gear from their cones:
Cone and gear were not only secured by means of a press fit.
The external toothing of the gear wheel was deformed in such a way that a form closure was achieved between the cone and the gear wheel, thus preventing axial displacement of both components.
To separate gear and cone the deformed section of the gears external toothing needs to be sheared off. For both 2nd and 3rd gear a force of approx 50 kN was necessary:
Now the the gears can be fitted with new cones (available at ZF).
We still have to decide whether to secure the cones with loctite only or laser welding.
