you can try to set them in mineral spirrits i have boiled them in water on the stove . or get them very warm and set them in the mineral spirrits.BE VERY CAREFUL YOU DO NOT BURN YOU SELF UP .when you let them sit for a day or two in the mineral spirits you can try a small o ring hook tool and try to hook them at the ring end gap DO NOT PRY ON THE RING LANDS . but try to work against the ring gap if the ring lands are nick up or cut up the pistons are junk the rings will not seal and do not hand sand or sand blast if you do bead blast the ring land go very lite when done the rings should turn smooth on the ring lands if not they are junk this takes some time