I posted this once before. Years ago, Joe Breeze helped me fix a large dent in an Eddie Soens track frame. Since the top tube was mitered and welded to the seat tube and head tube, it was sealed off. Joe drilled a small hole in the top tube and tapped and then inserted an automotive grease fitting. Then he filled the grease gun with oil and used it to fill the top tube with it. Then he kept pumping and hydraulically popped the dent out from the inside! Last, he removed the fitting, drained the oil, and I was good to go!