i heard a water pump should not be able to move.is that correct? It is a 1995 RM250. there is no clogging in the pipes coming from the radiators with 2 fingers require force to move them but with the 1 finger it requires no force to move a couple Centimeters.
The water pump is turned by the primary gear on the crankshaft. When you were turning the water pump - the crankshaft was moving the piston up down in the cylinder. The couple of centimeters of movement is just the play between the gears - that's normal.