So I have a 2013 Tao Tao 50cc, it runs and great when it starts. my problem is I can't keep the new variator on the shaft. The variator assembly is held on by one nut at the end of the shaft, after about a week of my daughter riding it, the nut will back off just enough that the starter wont engage. I have fixed it 4 times, then I took it to a shop, they couldn't find anything else wrong with it, other than the issue I just described. Just wondering, if anyone has ever had this issue. Thanks, and I will watch for responses.

 

Can't say I have had this problem, but I assume the pulley is splined? I have had lots of problems with rear hubs as, if the splines on either shaft or hub are a bit worn, the thrust change from drive to overrun and back makes them move behind the nut and slacken it, even pinned nuts come slightly loose. You could try thread locker on the nut, but if you have a worn spline, not much will stop it loosening the nut.