what could be the cause of the bearings being stiff in my inner c.v joint?

HI. I HAVE HAD TO STRIP MY INNER C.V JOINT ON MY VAUXHALL CORSA BECAUSE IT NEEDED MODIFYING TO FIT MY NEW GEAR BOX.When i have put the bearings back in the c.v they are very stiff and have not got free movement. they are ment to be able to move around freely and smoth but they dont. i have been told that the cv could not have been bent out of shape because it is made from hard metal. what else could be the cause of it?