Certain types of white spirit will do the trick. Here in the Netherlands, the two closest equivalents are terpentine (not the same as what in English is called turpentine!) and wasbenzine. If you add the former to enamel paint to make a wash, or use it to thin enamels for airbrushing, small parts will very likely become unglued on your model.
However, this looks like it’s too big a joint for that to work. The only options I see are to saw it through like Richard suggests, or to remove the teeth from one of the two sprocket rings and re-glue them in alignment with the other. I think I’d go for the former. Oh, and you can align the halves easily enough using the track.