The expander may be the problem, but only if the ring set was very badly designed, made, or installed (some expanders, particularly those made for cars, can be "crossed over" at the ends when you put them in the ring groove, and this causes the ring not to sit right down in the groove). I've made my opinion of the design of Victa 2 strokes known several times, and won't go into it further. If the excessive friction problem is solved by removing the expander, then you should remove it because using it may ruin your engine, but you should bear in mind that the bottom piston ring may not function properly without it.