Remove the piston and
gently move the ring. It should be free in the entire groove. Pay
special attention to a locating pin which may be present on some
pistons. This is a little pin located in the ring groove.
If you have a stuck ring.
DO NOT FORCE IT. The ring must be perfectly round and flat. Heating
may help to loosen it. You can go up to 400 degrees F. Don't go
higher as it may start to change the structure of the aluminum.
I will try to add pictures
in the future.