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?

Normally BB spindles are heat treated to a point where there's very little ductility and they'll break before bending. However, I have seen a few bent BB spindles in my lifetime. It's till more likely that your problem is in the crank or chainring spider.

Here's the definitive test. Figure a way to hold a pencil or other pointer steady at the height of the spindle. For example you could remove the pedal use a figure eight rubber band to hold a pencil on a pump which you hold vertical on the floor. Now turn the crank and watch for spindle movement vs. your reference. If the spindle is true, then the problem is in the crank.

In the future, don't pound away on an unsupported crank arm to remove a cotter. Support the crank arm with a block of wood or a short length of pipe, braced on the ground, so the hammer's energy stays in the cotter, and isn't used to beat up the spindle or bearing.

Sadly, the art of properly and safely removing cotters has gone the way of Damascus Steel, and folks are blaming the bike for the issues resulting from their own ignorance.

thanks ill give that a try

As FBinNY noted, hardened BB spindles are very unlikely to bend. I might also note that a bent spindle would not present as an "up and down motion" but rather a side-to-side wobble. The up and down motion you describe is more likely a result of the teeth on the chainring not being cut perfectly concentric with the bottom bracket axis. This is not unusual, particularly with less expensive road chainrings, and is not a functional issue. To eliminate the grinding on the chain guard, reposition the guard slightly higher so it clears the chain throughout the pedal stroke.

Well, Damascus steel has made a major come back in the cutlery industry over the past few years with makers and sellers making absurd claims for its magical properties, just like cottered crank users.

Yes, I see all kinds of claims about Damascus Steel, many of which involve what would be more properly called Mock Damascus Steel, or DS Look.

In any case, I don't think anyone makes any great claims for cottered cranks. It's just that they get such a bad rap from people who never learned how to service them. Like so many things, cottered cranks are easy to service---- if you know how.