So i have an old cottered crank peugeot and the chain moves in an up and down motion throughout each rotation. I have one of those old chainguards on there and i had to take it off because of all the grinding. i adjusted the tension and still can see the motion through each rotation.

Theres also a grinding sound throughout each rotation coming from what sounds like the bb....Theres no play in the crank arms at all and the guy at the shop said if a bb is bad theres always some sort of play involved in the crank motion.

Im just guessing its slightly bent.. someone probably was banging the hell out of it trying to get one of the cotter pins out in the past.. who knows

anyone else have this problem?