a few tips on engine modding, NEVER ever try to mess with the port timing with hand tools you need very accurate computer controlled stuff to do that without stuffing it up, you can polish just about every surface inside the engine safely but the inside of the piston sleeve, and rounding off the bottom of the piston and piston sleeve with a hand file and very find grit sand paper, then polish, just make sure you dont touch the inside of the sleeve..

last thing, never do it on an engine you cant afford to loose, because you could still stuff up and accidentally scrape the file down the inside of the sleeve, if you do that, lean it out as much as you can and give the poor thing hell for the rest of it's short life.