Kawasaki would of release there first kx450 in 05 if it was not for frame failure so they soughted the bugs out first ,06 was pretty good ,but i have seen a 250f ,i think broken in half ,loose engine bolts ,loose steering stem does not help either ,i saw a kx250 04 2 banger crack at the top spars ,tank and seat juntion witch i put down as loose bolts ,i saw a pro frame 97 i think had a small crack at top shock mount but that had a zillion miles and jumps on it.Now yamaha s have had many frames crack all alloy ones to ,late models as well,yz 450 comes to mind ,front downtube ,this was in mxa mag ,it was a manufacture fault ,plus the 2 stroke model i saw had a massive crack where top tube meets the side tube ,another place is down neer the footpegs.If the factorys have trouble ,imagine the poor guy trying to do these mods are having ?Extra gussit guys and correct technique and materials is needed .I remember the 1980 kxs had frame breakage in a big way ,and you could get a gassit kit to solve the promblem as well as a another frame with a different part number most likely the same frame with the gassit all ready installed maybe?The 81 kx seem to be ok.