No, I have not heard of this problem occurring with any other NC250 engine in other motorcycle.
I'm pleased to hear that many RX3 owners have reported their valve clearances have stabilized.
However, if you ride many miles and the valve clearances
won't stabilize,
something is wrong.
__________________
Spud
"Never argue with an idiot. He will drag you down to his level, and beat you with experience."
Mark Twain
2015 Zongshen ZS250GY-3 (RX3)
2006 Zongshen ZS200GY-2 (Sierra 200)
2005 Honda XR650L
2004 Honda CRF250X
1998 Kawasaki KDX220
Mods made to my Zongshen ZS200GY-2:
http://www.chinariders.net/showthread.php?t=6894