I don't think they need to be cleaned all that often but I will wipe the inside of the barrel down with a light coat of worm oil once in a great while. If you're noticing some chatter or sticking when you're injecting maybe take a second to pop the nozzle and just give a quick wipe inside that way to see if it helps any. If things persist it won't hurt any to pull the screws and clean things up. As far as a schedule for cleaning, days, months, hours, etc, there really isn't one.