When I inserted the pulley on the motor shaft, there was some little side mouvement. It was not extremely major but I found this simple solution that could of fix this problem fast and it was free.
This sort of slack was due to me machining of the motor shaft. The “D” slot ( D-bore) was the problem.
The solution was to make a shim to go between the shaft and the belt pulley to prevent the mouvement.
The coke can makes perfect shim. It measure 0.0035″ ( 0.09mm)
Very easy to cut and make the shape you want.
Making a triangle helps to insert the shim under the belt pulley.
With this solution, I was able to remove the slack in the belt pulley and the shaft. After a couple of hours on the scooter, I saw the shim disintegrated or simply not there when I remove the pulley from the shaft. It does work for a certain amount of time. The shim took the same colours has the shaft and was extremelly hard to see.
The first time I did not see it and the second time I removed the pulley from the shaft, it was there but hard to see.