Thank you, Weld.
Regarding the welding, I must confess I got lazy. I should have posted, "I coaxed my good friend Andy to weld some extensions onto the center stand."
I will go back and correct my post.
I did a little stick welding back in the 90's, but I need to get that Eastwood welder you recommend.
The board adapter works very well. It provides a nice, wide and stable platform for lowering, and raising the engine into place. I used it to remove the stock engine, and install a Yamaha XT225 engine in my Zongshen Sierra. The adapter worked equally well with the NC250 engine in my RX3.
I have not confirmed any other valves which fit the NC250 engine. Of course, the problem might also reside with the valve seats.
So far, the valve clearances are holding.
I hope the new valves and cylinder head have solved the problem.
Incidentally, I also installed four, new valve springs during this engine work. The cam chain was in very good condition, and did not exhibit any elongation, as the timing marks aligned perfectly.
__________________
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