I am in the process of converting my 83 mirage into a fixed/flip-flop. I have already purchased the mavix cxp 22 wheel set, but I am a bit confused on the crank situation. I think my bottom bracket uses the swiss style threading, so I don't know what is compatible. Can I use my old double crank? With either the 52 tooth or 42 tooth crank?

Thanks for any help/info to better my circumstances!

Motobecane=French for motorcycle. I think it has uh..French threading.

well, the ones in the 80's used swiss style

is it cottered or cotterless?

mine was cottered and I assumed swiss threaded. needed to work on the bottom bracket and was considering getting the threads chased to accept standard threading, but somebody stole it. made my decision easier.

It sounds like you've already verified it's Swiss, and of course it's easy to tell as the fixed cup would be left-threaded. Motobecane did both French and Swiss at various times, so you'll want to be sure.

Either way, replacing the bb will be expensive and/or difficult, so just use your existing adjustable bb. The crank that's on there is probably just fine; in a lot of cases, people "upgrade" from well made stock cranks to inferior replacements. Check the chainline using the existing double, and consider that you may be able to move one or both of the chainrings to the other side of the spider as well. If you can't get your chainline sorted out that way, you can use spacers for the chainring or try a different spindle length, though spindles are getting harder to source.

Most Motobecane's stopped using french threading in the mid 70's. My 76 Super Mirage has swiss threading.

Just use the 42 on the inner ring and you will be fine.

It has a cotterless crank. I guess if I use the 42 tooth inner ring it should be fine. But what about the outer 52 ring, do I have to leave it on? Also, would I be able to change out the pedal arms because I want something smaller than 170mm

Here is a pic of my crank for kicks:



Thanks for all your help.

Can't tell for sure in that pic, but is the outer chainring built into the crankarm? If so, obviously you can't that apart without some cutting, which is bound to look ugly. If the inner ring is removable (looks like it is), you could take that off and use the outer ring, but this would probably require a shorter spindle and it's quite possible the ring won't clear your chainstay at the proper chainline.

Just use whatever cups you already have and buy a spindle sized to get you the required chainline. BB cups almost never wear out.

Hey guys where are you buying spindles from these days, everyone laughs when I try to buy a new spindle. You know he may get lucky with the chainline being ok. But he could upgrade his cranks to like a sugino unit (about 50 for the cheap one) and then he could use spacers to get everything in alignement? That would be easier than FINDING a new spindle that is the right size (they don't make them anymore). Or am I totally living in a different century. But Keep the BB it's better than a new one anyways.

The spindles are indeed hard to find now. A couple of years back, it was a lot easier, but supply seems to have dwindled rapidly.

I don't see any point in replacing the cranks unless they're shot or they're the wrong length. The stock cranks on older bikes are often just as good as the basic Sugino/IRO/Pake/whatever.

Easiest thing to do is go with your existing crank. You can't take off the 52 ring. If you want something shorter than 170mm, you will have to get a new crank which means that you will most likely need a new spindle as the chainline won't be correct.

Do you have any LBS's near you that deal in conversions or have used parts bins?

I just realized that the other pedal arm (non crank side) is a sugino brand one. Also, what do you recommend I use for the rear cog if I use the 42 tooth ring? I won't be going up many hills, mostly flat land.

70 gear inches is a good place to start, this would mean 16t for you. YMMV

See: https://www.bikeforums.net/singlespeed-fixed-gear/468351-gearing-primer.html

If the chain line is good then leave it alone, but if he can't move the chain ring (like it's part of the crank permanently..you know), then he could easily switch out cranks and use the chain ring spacers to help him get the right chainline. But my guess is the chain line will work. Google sheldon brown AND chainline to find more info on chainline (Sheldon is my god).

I have an 83 Super Mirage, which is nearly identical - just one notch up the ladder. Your crank is probably a three-piece, so just take it apart & use smaller single-stack bolts for the inner 42t crank.

You might get a close chainline by flipping the spindle so the "short" side is on the "drive" side - this will bring the crank closer to the BB. I just did this successfully on a Schwinn Le Tour and got the chainline within 1-2mm.

This bike is full of odd threading - mine has a French-sized stem, outer seat tube diameter, and a Swiss or French BB. Unfortunately I love the paint & style so much that I keep messing with it, despite the higher weight of 2040 hi-ten. Post pics of yours when complete.

I'm actually going to have a bicycle shop in Oakland re-thread the bottom bracket for 40 bucks. I think it's a good deal, and now I'll be able to fit another crank. I'll post pics when I finish the bike (later this week). Thanks for the help!

The inner "crank" aka "chainring" is attached to the outer chainring, which is permanently affixed to the crank arm. These cranks don't have a spider like most cranks:



The outer chainring acts as the spider, and the inner chainring attaches to it.

Three piece means that the crank has two separate crank arms and a bottom bracket:

Just finished putting mostly everything together. I have yet to install the fixed cog, I only put the single speed cog on so far. Here are a couple pics from my camera phone.

your seatpost clamp is on backwards.

How much did re-threading the BB cost you? I have a 78 Mirage which is swiss threaded and I can feel things starting to wear.

It cost me $45 (half hour labor).

It is?

meant seat clamp.

how tall are you? that frame looks pretty big and your seat is pretty low. If everything is adjusted n your pics, that frame is too big for you