You can do this, especially if you have an intelligent question, or interesting insight. I have emailed top people in various fields with specific questions and gotten answers. They usually won't want to do a private tutorial to someone with no knowledge of the field, but if there is some ambiguity or possible error in a paper of theirs they pretty much always will respond. I have also on a number of occasions made cold calls on luminaries in fields when I am in their city, and when going to conferences the opportunity to meet and greet are one of the main purposes.
I also receive cold calls, visits and emails from people interested in the couple of fields where I am known, and I always respond positively to them. My email responses get more spaced out if there's too much tutorial, but brief yes and no questions, or interesting comments are pretty much always well received. I don't really like getting phone calls, but I have had some pretty interesting conversations with people who managed to find my phone number, most of these are from people overseas.