The problem is not the mechanics of getting there, I think those ideas have been drawn out ad naseum. The problem still remains that if you affect the past, which you undoubtedly will, you will affect the future in ways that will likely prevent you from going on your quest in the first place. If things change back in the time you came from, then the trip is unlikely to have taken place, or it took place to a different time, or it took place but you failed and died, etc. There is too much that can and WILL go wrong that it is just not plausible.