I have recently had the sprag clutch on My TTR replaced as there was a noise when you switched the bike off.
The mechanic that did the job said there was significant wear on the sprag you could rotate it both ways before it would lock up. The Boss gear he said had a little bit of wear but he didn't think it was anything to worry about.
Went to pick the bike up today and there still is a noise on switch of similar to before. Its entirely possible that I am being paranoid but I'm worried we should have replaced the gear. Does anyone have an image of a worn boss gear that needs replacing so we can compare? Also does anyone have a video of a healthy bike being switched off?Steve said he would send me a you tube video of his but I thought i would ask while i was here it might save Steve a job. Unfortunately I don't know anyone else with a TTR to compare it too.
It is really difficult to give advice without actually hearing your sprag when you shut down.
Even with a new sprag, there will be times when there will be kickback, usually on a stall when the engine is cold. If yours shuts down with a click most times then I would suggest you don't have a problem.
The surface of the boss needs to be darn near perfect and, if you could feel a wear ridge with your fingernail or see damage, then it definitely needs swapping out. Sorry - I don't have a picture of a damaged/worn Gear 3 boss.
Loads of information here - https://ttr250.activeboard.com/t49867440/sprag-clutch-questions-and-answers-thread/