I don't have any answer besides...When they are worn. Subjective at best since there are no wear indicators on the sprockets. Seems like I can feel when they start wearing the drive links funny on my chains when in the hand.
But really. I’ve cut approximately 60 cord with my MS362 and only changed the rim sprocket maybe once. Also the spur drum on my ms251.
When the chain stops-a-turning, I replace the sprocket. Well, maybe not THAT long, but I go a long time.
