someone has a washer or spacer put on the backside if the jackshaft in the chaincase, just remove the chaincase. you can do it the easy way:
1.) which is to loosen up the track tension.
2.) then remove bottom bolt and top nut, slip off chain and gears
3.) remove 2 bolts holding caliper on case-12mm heads, flip caliper over out of the way.
4.) remove 4 mounting bolts for chaincase to frame-14mm heads
5.) grasp the chaincase and the brake rotor and wiggle it off the shafts as 1 unit, leave parking brake intact and connected to rotor.
you will now find out whats wrong with the jackshaft being spaced wrong, the spacers in the back of the chaincase are in wrong or washers added, something is wrong on the backside.
you dont have nearly enough threads showing with your topgear on and nut, thats why its sticking out on the clutch side.
theres spacers that sit in the backside of the chaincase, should be a spacer with a 0-ring that fits inside it inside the chaincase/seal then the brake rotor, then the washer then the snap ring.