If you have to strip the motor, because of seized rings, as 1460 says, steep the crowns in solvent/diesel. If still stuck, put meths in the crowns, and ignite. Usually frees them off. When free, remove rings carefully (one piston at a time, to save mixing up), soak some string in petrol and using the ‘Diablo’ method, clean the ring lands out. Refit if serviceable.