A bit late response , But I finally had the time to take my gun apart.
It seems there's a teeth missing on of the gears
Also the piston head doesn't have alot of compression on the cilinder, I can move it back and fort without alot of compression.
Wich piston head and gears set should I buy ?
EDIT
Now I got it !
I didn't know it was just a V2 mechbox with long nozzle
I'm gettining some sytema helical gears ...