have got my lad a ktm 65,how often do you need to change the piston and rings,is it rings then piston/rings and so on.
my lad is not fast,i want to keep on top of bike but not throw money away and change if not required
I do a ring and little end bearing at 25/30 hours and piston/ring/little end at 60 hours and carry on with that cycle,this is a kawa 125.I find the piston is 2/3rds worn on the gudgeon pin holes with them starting to go 'oval' when spec'd up,same with the pin.The engine is worked very very hard and this I have found to be my ideal timetable to work to,depending on piston wear you may get 3 ring changes to the one piston depending on how hard the use is the engine gets at the track.I find by 25 hours on the bottom end drops off and my son then tends to abuse clutch more so in the long run it saves clutch.
When my lad was on the 65 I changed his piston about once a year!!
I do think we change pistons far to regular just for the sake of it, my lad is now on the 85 the bike is a year and a half old and on its fourth piston, we ride every weekend, ktm recomend a piston every 20 hours, Ive just changed a piston - its been in since about august, I put a ring in it around chritmas time and the piston was in good condition when it came out and we did the full wilden lane series through the winter