i have a 70s peugeot i converted to fixed recently, and i have an almost straight chainline. its not bad that my chain falls off a lot, just maybe like once every other week so its not terrible, but its less than ideal. do i have to get a new bottom bracket with a smaller spindle? and since my bike is so old i need to get a french BB. or is there anything else i can do that may help? and if i do need to get a new BB, i have only found french ones in spindle lengths of 107 and 113 by velo orange. any idea which i would need? thanks

To get a general idea of where your chainline _should_ be, run a piece of string from the cog to the bottom bracket shell. Then measure the distance between the chainring and that piece of string. Next, measure the space between the inside of the crank arm and the bottom bracket cups. If the first measurement is less than the second measurement, you should be able to replace the bottom bracket without having to swap the crank as well.

After you've done your initial measurements, remove the crank arms and the bottom bracket. You can determine whether your BB is French by noting the direction the fixed (drive side) cup is turned to remove. Once the bottom bracket is removed, determine the bottom bracket spindle length. Sometimes the length is stamped on the spindle itself, if not then measure.

Subtract your "ideal" chainline measurement from the spindle length measurement, and that gives you the new spindle length required to correct the chainline.

Another alternative is to dish and space the wheel. Give your LBS 20 bucks, and they'll center the rim relative to the center of the hub.

Chainring on the inside usually provides a usable chainline on the Peugeots.

You could swap out the spindle for a shorter size. Keep the BB, though, and save some dough. It would be a primo time to clean everything up and put in new bearings and grease.

Depending on the cranks on there, if your LBS is on point, they'll have a puller for stronglight/TA threads.

Thanks a lot. I tried moving the chainring inside and now my chainline is almost completely straight. and now to get the cranks off and clean up my BB. i'm gonna try these, https://www.jacobschuck.com/product_details.asp?pid=29,
cuz even if my lbs has a french crank puller, they would charge me just for getting the cranks off and maybe try and get me to buy some other stuff from them cuz thats how they are.

A 70s Peugeot is almost certainly French thread. If you get the cranks off, you can open the bottom bracket and inspect the cups. If they're in good shape you can simply replace the spindle to get a better chainline.

Depending on the crank, you may be able to sell them on e.g. eBay for enough $$$ to buy a modern crank to mount on a new spindle using your original cups.

Any pictures of the cranks?

these are my cranks, they are old Stronglight TSs, but mine have a nice chainguard on it.

but now that i moved my chainring to the back i have a straight chainline. and i would like to keep these if possible cuz i really like the way they look. and also i have been checking out these sealed cartridge BBs. https://www.amazon.com/Orange-Grand-C.../dp/B004JKGQXW
they come in 113 and 107 spindle lengths. you think it would be worth it?