I couldn't remove just the impellar part on my 94 rm 125 either, even though it had an allen screw on the end of it. I hade to take off the case half (kick starter clutch basket ect.) and remove the "C" clip from the back side where the water pump gear is, then i was able to slide it out. The new one came with the impellar already on the shaft (they might have a type of loc-tite on them or somehting). Either way I never could get it off but I didn't try to hard either. hope this helps- bjawes