Re: [CR]Motobecane Grand Touring crank and chainring hell

(Example: Framebuilders:Bernard Carré)

In-Reply-To: <BAY106-F349AE5C35A8DF5D0A7A013DA190@phx.gbl>
References:
Date: Sat, 30 Sep 2006 11:57:04 -0400
To: "II LONG" <r4959l@msn.com>, classicrendezvous@bikelist.org
From: "Sheldon Brown" <CaptBike@sheldonbrown.com>
Subject: Re: [CR]Motobecane Grand Touring crank and chainring hell


Richard Long wrote:
> So, I have this bike that I've spent a
>longggg time restoring and it has French BB
>threads (right hand, 35mm x 1mm) and I can deal
>with that. The cups are in good shape and so is
>the spindle. The crank is in good shape as well
>and polished out very nicely.
> Then I examined the chain ring which I knew
>would have to be replaced, and it suddenly
>dawned on me. . . What the heck is wrong with
>this chain ring, it doesn't have any
>spiders/arms on it! The sucker measures 110mm,
>C-C on the large ring

Multiplying that by 1.7, indicates a 187 mm BCD. I have never heard of a crank/spider with such a large BCD.
>and 70mm, C-C on the small ring.

SR did use a 118 mm BCD, divide by 1.7 and you get 69.4. Those chainrings are extinct.
>Did I mention that it's a Japanese SR, and the
>spindle measures 142mm end-to-end.

When measuring BB spindles of the nut or "maxy" type, where there's a male thread sticking past the end of the square taper, you do NOT measure "end to end", you measure only from the end of the tapered square part.
>What a Japanese/French/Frankenstein!

Actually, that's one of the nice things about Motobécanes, they were the first French company to abandon chauvinism and spec superior Japanese parts on their bikes.
> But I love the frame, which was just
>painted a beautiful red, with bright yellow
>decals and stunning yellow pinstripes not yet
>finished (damned artists), and I don't know what
>to do about this stinking crank and it's
>freakishly shaped chainrings. Sheldon Brown,
>are you out there? Are you listening? Can you
>see the pained expression on my obsessed with
>old bikes face?

If the chainwheels are toasted, my advice is to upgrade to a newer, better crank.

Sheldon "French Frames, Japanese Parts" Brown +-----------------------------------------------------+ | If you want fancy, complicated moving graphics, | | get a television set! | | Beer and car advertisements on TV are way | | beyond anything on the web, and load instantly. | +-----------------------------------------------------+ -- Harris Cyclery, West Newton, Massachusetts É-U
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