purchased a used 121-3. prior owner replace drive sprockets, rubber tracks and idler wheels. I have used it over 40 hours and love it, but I have popped a track off more than once. I am working in very rocky mountain soil and small rocks are always trying to get in there. THe track tension is according to owners manual. When driving on flat ground, tracks are quiet, when on a slope, front teeth make plenty of noise.
thanks,
Dave
thanks,
Dave