Pretty much whenever I go biking my chain will get jammed or will fall off, usually when I shift gears, but sometimes just randomly it seems. Its been like this for two years and when we took it to the bike repair shop they said there was nothing wrong, but when I rode it again the chain kept on doing the same as described above. I have a couple of bikes laying around which have bent frames in addition to my bike, do you think there is any kind of home repairs I could try? Any input is appreciated, thanks