I'm rebuilding an engine that has been sitting in the back of my shop for about 20 years some pistons are rusted tight to their cylinders. I've been soaking the cylinders in brake fluid and liquid wrench for a couple months off and on and even taking a piece of wood and hitting it with a hammer to break it loose to no avail. I've heard of using coca-cola but I just don't think so. Any ideas or thoughts?