I'm in the middle of restoring a 1983 Trek 520. I bought a new seatpost to replace the old one and I'm having a lot of trouble getting it to 'fit.' I have it in the correct size but I can barely get it to fit down into the seat tube. I'm greasing it and everything but I'm fighting it just trying to get it to slide in.

The original post was very very short, and the new one is long.. which makes me think that for some reason since the old post was barely inserted into the tube is why the new longer post is so difficult to get in - like it hasn't been stretched out enough or something for it to fit very well.

Does this make sense? Anyone ever have similar issues w/ an older frame? If so, could someone give me some pointers on how to get it to fit better? It feels like I almost need to spread it out slightly..I wish that were easy..haha. Any help is much appreciated, thanks!