Please forgive me, I know this is a question I've placed in the wrong forum, if You need to remove. I understand. I've never had the clutch (right) side off my DT-250, but my RD 400 is having issues, so im getting familiar with it. Figuring most Yamaha 2 strokes are similar Just needing to know if there is a way to install a replacement kick axle gear assembly w/o removing clutch/basket ? Kinda goofy, the old one goes in...? I watched a YouTube where the guy does install without clutch removed. Made it look way easy....mine not so much..thank You folks.

I've been there but was a lifetime ago. If you mean the gear on the kick shaft then yes that shaft should come out without clutch off. If you mean the intermediate gear then clutch needs to come off. Be unusual for a kick gear to fail without other issues being involved?. When refitting the shaft assembly be sure to engage the friction clip in its guiding slot as tensions the gear which causes it to engage when ever kicked down. Cheers from NZ.

Thanks RT, I am needing to install a replacement one, if it was currently possible, I would post a pic of the issue. The inner most gear end of the shaft has some missing /damaged teeth. The piece that serves as the stopper on the end of the shaft when up against the boss of inner case comes off the damaged shaft.. The replacement one I have doesn't. Oddly, I don't see any damage to it. I expected there to be considering the condition of the end of that shaft. There is a vid on youTube of a guy placing the shaft in and out, BOOM ! with clutch untouched. Makes it look so easy. I really hate the idea of having to yank the clutch, but if so, no choice. Thanks again to You !

Broken stop is unheard of on an RD400 twin in my experience.
But the first thing that comes to mind is that the motor has started & run backwards which is possible with pretty-much any points ignition twostroke.
Was an almost regular event on CT2 175 trail bikes if the points closed down through fibre heal wear so timing gets too close to TDC.
When they start & actually run in reverse & if you touch the kick start it drives the lever & stop back to the case & would break the case apart at the intermediate gear if you had a few revs on.
Would be running a bit grumpy so Mr Farmer would give it a good rev & accidentally touch the kick lever then its all over.
Or brake the shaft where intermediate gear sits on.
Yamaha started adding a diode at the coil so that if it kicked back--it couldn't start in reverse.
Just look closely at the intermediate gear on yours if you can eyeball it being shrouded by the clutch.
Best of luck--if i understood your story correctly!!.

Thanks for Your advice. Will do.