Hi everyone,
I'm new here, so bear with me please...

I'm trying to fix up this bike a bit so it rides smooth and well. I'm in NYC, and it's going to live outside on the street. I've gotten the anti theft pinheads for the Mavic wheels I put on it, and use a good Kryptonite to lock it up.

My question is about chain wheel and cranks. I'm having trouble with chain suck on the chain ring between the smaller and the larger chainwheel. I'd like to replace the chain, the cranks and both chainwheels (this time without having a chain gaurd!) without changing the bottom bracket.

. CHAINWHEEL SIZE I can't workout the size of the chainwheel - the larger one seems to be 210 mm, which I think means it's 52T, and the smaller one seems to be 40T though I'm not sure. Can anyone enlighten me?

. CHAIN SIZE Is the chain size 3/32", and what's a good quality chain to use on there to replace the one I have? I figure I might as well do this too, while I'm changing everything else.

. CRANK SIZE & TYPE The cranks are 190mm, but I'd be fine with 180mm or 185mm. Don't know if anyone as amateur as me would even notice. I'm only 6' tall anyway.

Can I replace them with a cotterless crank and chainwheel set? I like the look of the Stronglight 49D for example but have no idea if that would fit onto my bike - I assume I'd need a new barrel? help!

. TOOLS What tool do I need to unscrew the bolts on the chain wheels? Is there a tool or do I just use an adjustable wrench to get everything off including the cotter pins?


Thanks for any and all help!

1. Count the number of teeth on the chainrings. A combination of 52-42 or 52-40 is fairly typical.

2. I would use the cheap KMC 5-6 speed chain. The last time I bought one it was about $8 at a local bike shop, although it was not in a high cost region of the Country.

3. A crank length of 190 mm is really long. More typically you'll find 165-175 mm. You'll probably want to be towards the upper end there.

4. If you're going with a cotterless crank, you'll need a new bottom bracket. Luckily, Velo-Orange now supplies a modern style cartridge in the French threading standard.

I'm not that familiar with the cottered crank aspect of your inquiry, so I'll leave that for others to sort out.


edit: Are you planning on putting the rear brake back on? I recommend that you do.

- what's it mean that "it's going to live outside ..."? meaning, overnight on the street in the rain? not a good idea for any bike.

- i like the sram pc830 chain. i put it on all new builds. it goes for less than $15 shipped on ebay.

- definitely install a rear brake unless your bike is a fixed gear. you need a backup. this actually saved me recently when a front cable i had worked on the night before slipped through its anchor. it only needs to fail once for this kind of thing to leave a lasting impression.

- count the chainring teeth to determine diameter. there's a formula for estimating bcd -- see sheldon brown on that. 144bcd is a popular size for the vintage, but your small ring will be limited to 42t, no smaller (for all practical purposes).

- if replacing the cottered with a cotterless, i'd let your lbs remove or loosen the cotter pin and crank, and you can do the rest probably with the cheap $15 park spanner wrench and an adjustable wrench.

- happy riding. i bet it's a lot of fun riding in nyc...

Thanks guys!

I might take your good advice on rear brake but not for the moment I think. I'll post photos if that goes badly... that said riding in NYC is the best. It's so much faster and more pleasant that subway or cabs and a lot of fun.

Seems my chain rings are 52T/40T

I ordered a new SRAM 850P, which people seem to like and it seems pretty tough and easy to use/clean.

I'm trying to measure the BCD but I'm having trouble - I got a measurement for 100mm between the two visible bolts, but another for 55mm between one nut and the other bolt - I can't work out if my chainring is a 3 bolt or a six bolt... can you guys help? *I think it's a 110mm six bolt, but is that wrong?*

Thanks again for all of your help!


I'm looking into the BB, and I read that they're often Swiss thread in the Motobecane from this period - is that right? How would I tell?

french threads have a different width between the threads than british/standard. so, your bb and steerer tube (and maybe even pedals) have french threads. if the fixed cup of the bb on the drive side tightens when turning to the left (like most other bb fixed cups and left side pedal axles), we call that swiss threading. on the other hand, if the french threaded fixed cup is 'righty tighty,' we just call that french, 'cause that's just weird.

If you're going to replace the crank, then the BCD of the crank that's on it doesn't matter.

Any idea from the photos if my Chain Ring/Spider is a six or a three bolt?

It kind of looks to be a gray area. The spider is 3, the rings are 6.

But again, it doesn't matter since you'll be removing all of that and replacing it with other stuff.

I wouldn't leave any bike outside in NYC.

I would try to make due with the new chain. Replacing the crank and BB on a low end bike doesn't make financial sense. For the money you'll spend, you could buy a better bike. Are you sure everything is adjusted properly? Poor adjustment/bad chainline may be causing your chainsuck problem.

Those are steel chainrings and they should last practically forever.

Those cranks look to be 170. Are you sure you are measuring properly? (Center to center)

I just opened the BB and actually forgot to measure it... Oops. I cleaned it all out in there etc. I'll look at adjustments of the shifter and see its that's off-I feel like its not parallel with the chain which might be an issue. I couldn't undo the drive side cup, which is what makes this BB potentially different. Hmm.

Also, my new SRAM chain is about 8 links shorter than my old one. It seems to work, but needs adjustment. Does that sound right?

^ on chain length, i always follow the sram instructions which come with the chain, which says to place the chain around the largest ring and largest rear cog, pull tight, and add two links to this minimum measurement (even though you would never run the chain in this large ring-large cog config).

BB seems to be 35mm x 68mm, but I couldn't get the drive side cup off no matter what I did. I cleaned everything, and replaced the bearings for now. See photos below, in case anyone needs reference materiel.

My next problem is trying to get my front derailleur working. Everytime I try to shift it up, it goes over the chain ring and falls off. Sometimes when I shift down it drops between the two chain raings and gets jammed. I've taken the chain guard off to stop it getting jammed in there.

I've worked on the two tension screws to some success, but shifting up is still a problem. Either it falls off the edge (too far) or it takes 30-45 seconds after shifting up to latch onto the larger chain ring. There's no efficiency in it. I'm wondering if the mount is off - it looks as though it's not parellel with the chain, and off on a slight angle.

I know Sheldon Brown says maybe bending the inside edge of the cage out a little toward the frame can help, but I don't think that's going to help me here.

Any help please?

dude, what a filthy mess! start by taking the derailleur off and cleaning it up. i'd just drop it into a coffee can full of solvent like mineral spirits. or you can clean it by hand with a toothbrush and wd-40. take all the screws and bits off, clean rust with naval jelly if you have to and reassemble with a lubricant like parks lube. when it's all put back together, use a spray oil like tri-flo on the moving pieces and spring. while you have it off the frame, clean up the bb shell area and seat tube. reassemble on the bike using a lube between the frame and clamp. polish out any road rash with auto quality sandpaper. visit sheldon on replacement of the derailleur. it should be only a couple millimeters above the big chainring. the crank arm should clear through its revolution, and the chain should not interfere. if it's not bent, don't bend it, but use clamp placement to adjust. it's ofen a trial and error approach. hope you bought new cable as well...

Brilliant answer..! Will do, thanks!

And as Shedlon says, don't reuse the toothbrush for dental hygene purposes.

I think you should look up your local bike coop and have them help you get everything working properly.

Thanks for everything people. I'll keep tinkering-I'd very much like to learn how to do this myself. Kind of the goal here. You've all been enormously helpful!

Thanks man. I was measuring badly, they're 170... And my chain wheels seem fine, I think the problem is in my derailleur.