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Correct seat post bolt size 1979 Motobecane?

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Correct seat post bolt size 1979 Motobecane?

Old 09-17-20, 11:04 AM
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renrub
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Correct seat post bolt size 1979 Motobecane?

Anyone know the correct size seat post bolt for a 1979 Motobecane off the top of their heads? Tried 17mm - too big.

Thanks. - Pat.
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Old 09-17-20, 11:20 AM
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Better off asking IN Clasic & Vintage or asking mods to move this there.
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Old 09-17-20, 11:44 AM
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I tried there a few days ago, no luck, but thanks.
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Old 09-17-20, 01:12 PM
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Bolts can be cut shorter. I am assuming that the 17mm quoted was the length.
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Old 09-17-20, 08:13 PM
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No local lbs in Pittsburgh? Mine has chromoly seatpost bolts for $2.50/ea in two sizes.

I would think the '79 Le Champion uses a little different bolt than the '79 Mirage.
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Old 09-17-20, 09:55 PM
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I assume that measuring is not on the table. Andy
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Old 09-17-20, 10:43 PM
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So, what threading would the French use for a binder bolt?

Is there unique French threading on the entire bike?

That is probably a type of C&V question, as few people will know the exact size, but they may know the thread type.

I have no clue.

John
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Old 09-18-20, 05:25 AM
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Originally Posted by Andrew R Stewart
I assume that measuring is not on the table. Andy
I just picked up some digital calipers. It looks like 7 x 18.5mm, but the hole also seems a little oblong.

Trial and error it is then.
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Old 09-18-20, 08:16 AM
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6mm is what I've seen.
Buy the correct length to suit.
1/4-20 is SLIGHTLY larger dia.
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Old 09-18-20, 09:07 AM
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[QUOTE=renrub;21700198]I just picked up some digital calipers. It looks like 7 x 18.5mm, but the hole also seems a little oblong.

Trial and error it is then.[/QUOTE]
In your first post you stated that the 17mm was too big, but measuring up the area gives you 18.5mm;
are you sure that bolt was 17mm? If it was, and it is indeed too long/"big", go to it with a grinder or file, taking off equal amounts on the bolt and captive nut, and call it a day. Good luck.
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Old 09-18-20, 11:50 AM
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Originally Posted by 70sSanO
So, what threading would the French use for a binder bolt?
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Old 09-18-20, 12:48 PM
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Originally Posted by Bill Kapaun
6mm is what I've seen.
Buy the correct length to suit.
1/4-20 is SLIGHTLY larger dia.
Thanks very much!
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Old 09-18-20, 05:17 PM
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1979 Super Mirage seat post bolt size

OK, just for anyone referencing this thread in the future, I persuaded the seat post bolt that I bought on Amazon (that I couldn't get to fit initially), to work by using a large screwdriver to round the hole from oval, and a dead blow hammer to tap it in. Sounds bad, but pretty sure I didn't do any damage. The bolt is a sleeved and keyed Sugino Seatpost clamp bolt, 17mm - chrome. The diameter of the sleeve is 7.9 - 8mm. Amazon has jacked the price up by $7 since I bought it, so I would look elsewhere. But that's the size. Thank you to everyone who replied.
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