hi, its that stupid Chinese gearbox.
i have the same problem with the 2nd and 3rd gear.
at first it happened to only the 3rd
after a month the 2nd one screwed up.
u have to change gear box completely.
am going to change engine completely as i dont trust Chinese engine.
Actually ,the bike has a problem in its gear box. while i was in H.K.
i was at the distributors warehouse. saw a couple of mad ass with broken gear box.
In Singapore also i saw 3-4 mad ass with broken gear box at Mah.pte
and Mah motors near SC video game