I had a bit to do with kx85 owned 3 of them in the past , when you get the clearance checked and if all is well you need a hr meter to keep track of engine rebuilds , the harder it get ridden more often you need to do a top end , as well as keeping air cleaner maintain and good 2 stroke oil will help engine life , better to replace top end before it blows , i cant remember how many hrs i use to do the 85 top end but i know on our kx125 08 i change the single ring at 9 hrs and the piston at 18 hrs thats with a pro rider on it , lucky the parts are fairly cheap, hope this helps.