sincos Your frame could be any year from a 1979 to a 1981. Motobecane didn't use Shimano very often but Grand Record bikes during those 3 years came with 600 EX components.
Here's the Grand Record spec sheet from the 1979 Motobecane Catalog. The 1980 & 1981 catalogs lists a Shimano 600 EX headset instead of Motobecane.
The colors listed for 1979 are: New Blue and Gun Metal Gray but Oyster Shell (Pearlescent White) was used on Grand Records from 1978 to 1981.
1978 catalog cover page - before they switched to Shimano 600 ex components.
Your Shimano sealed bearing cartridge BB is stamped BC 1.37 68 which has standard British threads. That design was used successfully for decades on millions of bikes around the globe. You can still get quality Shimano replacement cartridges for ~$20 USD on line. Most Japanese double cranks should fit without a problem.
The headset is most likely British thread too which should take a 22.2mm inch size stem but check it out first. Is it wrong? Or just French!
Double Butted is an abused BS term used by marketoids. Only the Top Tubes and Down Tubes are Double Butted. With the exception of Asian frames made with some types of Japanese tubing, Seat Tubes are Single Butted. Steerer Tubes are usually Single Butted. So are some fork blades. All the rest of the tubes are Straight Gauge - no taper in the wall thickness.
Vitus 172 had the same strength and wall thickness as the Reynolds 531 tubing that was used on most Continental European production bikes: 1.0mm on the butted ends, 0.7mm in the thinner sections.
Your Grand Record should take a 26.2mm or 26.4mm seat post. The spec sheet says 25.2mm but that's a typo.
The rear dropouts are 126mm wide to fit a 6 speed hub.
Numbers stamped into Motobecanes and most other French production frames mean
NOTHING!!!
We're talking about bikes that were made up to 50+ years ago (~40 years ago in your case). The companies that made them have been out of business for 20-45 years - there is no longer any traceability for most of those bikes.
The Shimano 600 EX top lock and adjustable headset nuts take special wrenches that are rare. You can use something like Channel Lock pliers with GREAT CARE to avoid munging the nuts (wrap them in cloth???)
Lastly, the original head tube badge looked like this:
Hope this helps a little.
verktyg
