I have a Fisher Grandpa that I recently set up but am having problems mounting the stove pipe properly. The stove has the heavy ring on top that I thought the 8" stove pipe was to fit in to, but it does not want to slip all the way in. Is there another piece that is supposed to be mounted on that ring or is the stove pipe just being difficult. Tried to tap the pipe into place but couldn't get any where without damaging the pipe. Any ideas? Technique? Thanks in advance.