My Dart Swinger Project!

Ok gotta quick question. I got it torn down everything except one side i cannot get the pistons out. Im assuming the rings are catching on the groove at the top of the cylinder walls. Whats the best method to get them out? I tapped on them with a hammer and a wooden rod you can hear it when it bottoms outs. I took one out the bottom side and was just gonna take the rings off and push it back thru but then I noticed the middle ones i can't do that with them. So im stuck for now.

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