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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 03-01-08, 05:14 PM   #1
sdge
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Sizings on old Motobecane.

Okay, so I am trying to turn an old motobecane frame into a nice fixed-gear bike (actually I'm not really working on it, my friend is who is very bike aware and works at a shop). The problem my friend is running into building the thing is that the head-tube(?) seems to be 1" threaded but he can't get it on quite.

He says he thinks it might be some very odd size that he's not sure about. I believe he was saying he thinks he can force it on, but he doesn't really want to try. Does anyone know if this old French bike has a weird measurement there?

Also, he says the tube that takes the seat post doesn't quite want to accept the seat post (I'm not sure of the sizings here) and thinks he can force it in, but doesn't want to until he is more certain that the reason the seat post isn't going is because of some kind of warping or something in the old frame. Is it possible there is some irregular sizing here as well?

The bike is a Motobecane grand jubile (early 80's?).

Any and all help is appreciated. Thanks.
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Old 03-01-08, 06:11 PM   #2
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http://sheldonbrown.com/velos.html
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Old 03-01-08, 08:22 PM   #3
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Your friend may not know about the other differences as stated in the above link if he hasn't worked on vintage French frames...

However, if he is not aware that seat posts come in a variety of sizes, I would be concerned about going to that shop...
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Old 03-01-08, 08:43 PM   #4
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I'm dumb, sheldon brown has the answer to every bike question ever.
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Old 03-02-08, 04:34 PM   #5
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Originally Posted by sdge View Post
The problem my friend is running into building the thing is that the head-tube(?) seems to be 1" threaded but he can't get it on quite.

He says he thinks it might be some very odd size that he's not sure about. I believe he was saying he thinks he can force it on, but he doesn't really want to try. Does anyone know if this old French bike has a weird measurement there?
Your friend might be very good with modern bikes, but sorry, he doesn't know about old French ones. Sounds like the fork is French threaded. (Sheldon's link will explain this.)

If that's the case the BB might be as well, although from this vintage it might also be Swiss. Either way, your friend isn't likely to know about that either.

Sorry if this comes off as flip, but it sounds like you're coming a bit close to ruining a perfectly nice old French frame. I have a soft spot for those, being a Moto rider myself.
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Old 03-02-08, 04:53 PM   #6
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You need a vintage friend.

Where do you live? Their might be a C&Ver nearby.
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Old 03-02-08, 07:01 PM   #7
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French threaded steer tubes have a flat instead of a keyway for the no-turn washer. If you need a French headset, heres the best deal you'll find on one of the lightest and best French headsets ever made:

http://www.xxcycle.com/a9,,en.php

They're in France, but they ship fast and don't overcharge for shipping. I can get stuff faster from them than I can from Harris Cyclery.

If your bottom bracket needs to be replaced and is Swiss, it's a much bigger problem that if it's French. French is hard to find. Swiss is nearly impossible.
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Old 03-02-08, 11:10 PM   #8
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The bottom bracket is English. I've taken the frame to several shops and people have looked at it and seem to think that the headset is 1" threaded and my friend actually got the english bottom bracket in.

The 2 shops I brought it to said it was also an english bottom bracket as well.
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Old 03-03-08, 10:57 AM   #9
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The bottom bracket is English. I've taken the frame to several shops and people have looked at it and seem to think that the headset is 1" threaded and my friend actually got the english bottom bracket in.

The 2 shops I brought it to said it was also an english bottom bracket as well.

Good news about the BB. It would seem odd that the fork would be threaded French on a bike with a British BB, but perhaps it's not the original fork, or maybe it's not French and there's a problem with the threads on the HS you're using. But just to be clear, the steerer on a French threaded fork is 1"; it's just that the thread pattern is different. The other difference is that the inside diameter is slightly smaller, so you need a French stem, or you need to spend some time with sandpaper on a standard quill.

Here's something you might try - if you have a standard 1" quill stem (one that you know not to be French) try inserting it in the steerer. If it fits, you don't have a French fork.
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Old 03-03-08, 01:45 PM   #10
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I've used standard 1" quill stems with French forks and headsets before. The quill fits into the steerer tube, but the problem that I personally ran into was that the quill stem would not remain seated solidly inside the tube.
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Old 03-03-08, 02:06 PM   #11
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I've used standard 1" quill stems with French forks and headsets before. The quill fits into the steerer tube, but the problem that I personally ran into was that the quill stem would not remain seated solidly inside the tube.
Well, I can't dispute your experience, but the standard 1" threaded quill size is 22.2mm and French is 22.0. Your description sounds more like what would happen when inserting a French stem in a standard steerer.
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Old 03-03-08, 05:53 PM   #12
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The stem was an SR one and the bicycle was a Peugeot PK10N with a Stronglight headset. I'm relatively sure that it was French-threaded, but perhaps not.

Either way, it sounds like the original poster needs someone who appreciates a good French bike!
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