Front axle GPX 600 R, BJ.94

Hello, I have a question. My name is Ralf and I have a problem with the front axle of my new ( old ) purchased Kawa. I have the following problem and wanted to ask if you can help me further. I added a GPX 600 R, year 94 last month and wanted to mount new tyres for the TÜV. I have a problem with the front tire now. When solving the mother of the axle I noticed that this mother was only wearing a warm hand !!! I have removed the front wheel, which The distance socket and the screw for the tacho are correctly installed. But if I try to tighten the axle with the counterscrew (after I tightened the axle with the counterscrew ) now to tighten the axle nut of the axle, I can no longer turn the front wheel. It is then bombs fixed. But if I only put on the nut with approx. 20 NM, the wheel can be turned clean again. Something jams there and I don’t know what. Do you happen to have an ide e ? It can’t be that the axe nut is only dressed so easily. It would have to have normally around 90 NM. Thank you in advance Greeting Ralf