I "think" V2 feathering shaft is thicker... I can't remember where I heard or saw it but
you might find it here in Finless Bob's videos that he put out about the V2 upgrade
"Trex 450 SE V2 Overview VIDEO"
http://www.helifreak.com/showthread.php?t=29182


edited for this info...
I just found this info...

http://www.rchelicoptertown.com/foru...ead.php?t=2679
"V1/V2
V1 helis have a 3 mm feathering shaft, no thrust bearing in the blade grips, and bushes on the mixer arms. V2 helis have 4mm feathering shaft, thrust bearings and bearings on the mixer arms. All AE/SE Copterx have v2 tails."