Monday, May 20, 2019

Nearly There: Motobecane 650B Conversion

Well, the Motobecane Grand Jubile 650B conversion is nearly there. I still have a few odds and ends to complete - install toe clips and straps, wrap the bars, get some fenders, etc. - but it's definitely rideable at this point.

I've taken the bike for a short spin around the neighborhood to sort things out. It seems to handle nicely, and felt pretty good over the old brick-paved streets near my home (they're like the Akron version of cobblestones -- Akron pavé, if you will).

The red/black/gold color scheme is a favorite of mine. The paint looks pretty good from a few feet back, but up close there are lots of chips, scratches, and touchups to be seen. Never mind that for now. I'm not sure what the angles are on this frame, but the head angle looks fairly steep, and there's not a lot of fork rake. I could be wrong, but it seems to me that earlier versions of this model had a slacker head angle and more rake. Funny thing, though - the '77 catalog lists the Grand Jubile as a touring model. It's probably closer to that now than it was when new. I ordered some fenders from Velo-Orange, which I think will cap this project off nicely. 
I did end up cutting about ¾ inch off the ends of the bars, which seems to work well with the bar-end shifters, and makes them look a little more "normal" to my eye. I used Dia Compe 750 center pull brakes on the front and rear, with Velo-Orange pads. The pads are not quite at the bottom of the slots in front - but are pretty much there in back. I still need to wrap the bars (I'll use Tressostar black cotton tape with a coat of shellac) but I won't do that until I'm sure about the reach to the bars and the brake lever placement, etc.
Lots of space in the back. Fitting fenders shouldn't be a problem. For the cable hanger in back, I found a new-old-stock Shimano hanger with a built-in quick release. There's a similar quick release hanger on the front, but marked Dia Compe. Yes - my brake levers have quick releases built in, too. Used together, the brakes open up as wide as possible to let a wheel and a fat tire out easily. To run the brake cable housing along the top tube I needed to use cable clamps. Fun fact: French bikes use a 26mm top tube and most cable clamps are made for 25.4. I had some nice old Shimano ones that appear to be stainless steel instead of chromed, but they wouldn't quite work - the clamps themselves are flexible and seemed like they'd fit, but the supplied screws weren't long enough. I searched though my spare parts and found longer screws that happened to be the right thread and diameter. Yay!
This view tells me I need to remove a little excess cable housing - the "loops" look a bit big to me.
I did it again. Another SunTour Vx - this time it's the medium-cage "S" model. The bike would have originally come with a Cyclone derailleur set - but the Vx is reasonably light, looks pretty cool, and is darn near indestructible. Notice that the frame was built with SunTour dropouts. Older versions of the Grand Jubile used Huret Jubilee derailleurs, and I assume the Huret dropouts as well - and the derailleur hangers on those are not compatible with most of today's derailleurs (at least not without some modifications). SunTour and Shimano both settled on the Campagnolo-style derailleur hanger some time back in the '60s or early '70s, which pretty much made that the de-facto standard for the industry.
Up front, I have the SunTour ARX, a nice-shifting but under-appreciated front derailleur. I used the same Vx/ARX combination on one of the bikes I built for my daughters. I got the VO crank slightly used for a fraction of the price of new (the version with drilled rings would have been a nice touch, but that's how it goes). MKS Sylvan pedals have the right vintage appeal.

Always Brooks saddles.
I know I included the catalog and specs in an earlier post, but it's worth seeing again.

Being my first 650B conversion project, I tried to keep the investment low. I got the frame pretty cheap, raided my parts bins or bought lightly used parts wherever possible, and went with budget-friendly new parts where needed. I'll have to get a sense of how much I like the bike, and make sure the fit (and everything else) works for me. For one thing, I did go with a 25" frame (I normally ride 24") based on some recommendations from people who've done similar conversions. Going down a wheel size lowers everything enough that I can still straddle the top tube just fine - but I do wonder about the length/reach. We'll see how that works.

If I decide I really like it and want to stick with it, I do have some thoughts about things I might do with it later - like maybe sending the frame out for new paint and having some braze-ons added, such as brake pivots (either for direct-mounting the center pulls, or possibly cantilevers), and cable guides/stops, etc. But I'll want to ride it as-is for a while before I make any decisions like that.

Here are the full specs:

Frame: 1977 Motobecane Grand Jubile, Vitus 172 chrome-moly tubing throughout, 25".
Wheels: SunTour Vx hubs, Grand Bois rims, 36 Sapim double-butted spokes.
Tires: Pacenti Pari-Moto 38mm
Rear Derailleur: SunTour Vx-S
Front Derailleur: SunTour ARX
Shift Levers: SunTour BarCon ratcheting bar-end levers
Freewheel: SunTour Pro Compe, 5-speed, 14-28
Crank: Velo-Orange, 48/34
Pedals: MKS Sylvan
Bottom Bracket: IRD QB-55 with Swiss-threaded cups.
Headset: Velo-Orange (French threaded)
Stem: Nitto Technomic, 9cm
Handlebars: Velo-Orange "Course," Maes-bend
Brake Levers: Dia Compe 204Q (with quick release)
Brakes: Dia Compe DC750, with Velo-Orange pads.
Seatpost: Kalloy Uno, 26.4mm
Saddle: Brooks B-17

I'll get more pictures posted and a ride report when the last bits are finished.


  1. ARX FTW! The best thing about every ARX front or rear mech I've ever used is that I don't remember anything about them after the initial install and setup. They work. Period.

  2. I'll be curious what you think of the brakes. Every long-reach 650b conversion I've tried has terrible braking in the wet, even with salmon pads. Ride through wet grass, and the bike can barely stop after.

  3. Hiya Brooks- long time reader of your blog here...
    I did a similar 650B conversion of a 77 Motobecane Grand Record, also a 25" frame. Flickr album here:
    I've noticed that a lot of my boom era frames (all 62-63cm) have steep head tube angles compared to the shorter versions. I'm not sure why that is- totally illogical- but I guess that some price/efficiency factor drove tweaking the geometry for taller sizes rather than true scaling from small to larger.
    Someday, I'll make the effort to get my head around this phenomenon, but if you beat me to it, I'd love to read about it. Maybe one of the gurus can 'splain: Grant Peterson? Jim Mertz?
    Anyway- nice 650B conversion, and looking forward to seeing it in full dress!

    1. I looked at your bike - really nice. If I decide to make a bigger investment on mine, I might use that for some ideas. I notice you had a lot of items brazed on - brake bosses, pump pegs, etc. it also looks like your fork has more rake, less trail - did you have it re-raked, or have a new one made?

    2. The original fork was re-raked, but it would have required an expensive custom fillet-brazed stem with French dimensions, so I opted for a custom fork with a wider crown and standard size steerer tube with a stock stem from Compass. Work by Norther Cycles in Portland.

  4. Hi Brooks, I'm just getting back in the game, I rode constantly, in the early seventies, through junior high and high school, went from varsity, to a low end Raleigh, and spent years upgrading it, got it down to about 22 pounds with sewups.
    I retired from the Marines two decades ago, with multiple sclerosis, but fight with it every day, I'm a machinist I own a shop and live in farm country, N.C. I found a Giant in my shed, a couple months ago, digging out a couple shop heaters for a custom car/truck builder friend with a big barn, and found the bike, forgotten, and pulled it out.
    I've cleaned it up, new cables and such, tires, chain, put a Campi record front deraileur I picked off ebay, and it rides very nice, but with a tighter neck angle than I'm accustomed, I think. I have enjoyed it for getting my mail, (quarter mile driveway) and Raven can't keep up, so she lays down, waiting for my return, no more running in front of cars, but I had to build a bike.
    I picked up a frame cheap, dent in top tube from a crash, probably, grrrd up BB threads, and have concluded it's a Tange, and by that, found your blog. It's a 56cm, seat post, under 4 pounds, has shimano rear drops, make for 700c wheels, has round loops under bb, for shift cable guidance, appears to originally be 1.368 by 1mm bottom bracket threading, had to make a tap to un-mangle the threads, it arrived in a light brown haze, a bit of chrome on the rear stays, fork doesn't belong, but fits, with Campi drops, any idea what kind of bike this frame might have been from?
    Things have changed a bit in the last forty years, while in the Corps, I used a trek mtb for cross training, an 850, enjoyed it quite well in the uncut swamps of Carolina Marine bases, but I want my own built road bike, to try out with the MS bike ride, (never enough time for work) haven't made one (ride) yet, but intend this year. I picked up a pair of wheels with campi hubs, a 9 speed 13 to 26 cassette, 32 spoke wheels, a campi record crank set, 53-39, Shimano 105 brakes, and I've got several rear deraileurs, a couple later campi, a "nuovo record of 74 vintage, and a new Shimano 105, in case I can't make one of the others satisfactory.
    My last bike before entering the Corps in 76, had a regina, six speed 13-21 cog, with campi gran sport deraileurs front and rear, on a straight tube Raleigh frame.
    The "Giant" already feels better, lighter, better brakes (short arm Shimano) the front deraileur didn't like to shift up, and found a Campi record in my parts (separate from my Harley parts) and it works very fine with a suntour crank, original. Any ideas on what kind of bike the Tange frame came from? I'm just beginning to get back in, and everything's changed for some odd reason.
    Semper Fi,

  5. Hi Brooks, beautiful bike! I'm converting a Grand Record right now. It's been a big job. I should have gone barcons but I hate them ;) So I've installed ergopower. I'm trying a Campy-Shimano mix which so far isn't cooperating.

    Biggest problem has been with, as Eric above states, braking. Even in the dry the bike brakes horribly compared to my other brakes (which admittedly all have top-shelf braking power).

    I've found a front drop bolt adapter and dtswiss pads have gotten me into a level in which braking is more or less tolerable.

    I also switched to a Tange fork (sacrilege I know). The 65mm offset gives me a much lower trail. It's all chrome so aesthetics are still great, though not as lovely as the original fork.