ehcoplex 

Picked up this rough '79 Comp GS in January. I've been going back and forth about what to do with it, finally decided to build it up as a 650b conversion with some parts from the bin & some parts 'borrowed' from other bikes.
Before-



Today on it's shake-down ride-



I'd like to figure out how to make the Campy GS stuff work (I love the aesthetics of the 3-arm crankset....), though I'm not sure it'll be possible. And if there's a better friction-shifting experience than Retrofriction levers moving Suntour Cyclone mechs, I've never had it! I wasn't really sure what to expect- the test ride in the rain when I bought it, with old, flabby tires, hardened grease, rusty chain, etc. didn't tell me much. But wow- it's quite nice. Quick, responsive, but also stable and comfortable. This drivetrain will have to go back to the bike it was borrowed from, so I'll have to figure out what to do here.

Kabuki12

I just sold mine . I only sold it because it was a bit small. My 1977 was all original and in very good condition with the original GS mech. I changed the rear derailleur after the cage came apart. I was able to repair it but the Nuovo Record worked well and I left that on the bike. It looks like your Cyclone will allow for better gearing choices , I would leave it or find an equivalent.These are very responsive and light bicycles. I had many happy miles over about 8 years . I’m not sure , other than the 650 conversion , how you got those wider tires on . I was running 700 x 23 but probably could’ve fit 25’s easily. Joe

gugie 

That's a nice build!

Looks like you're running Gran Bois Hetres - kudos for mounting them with the label aligned with the valve stem. The Competition GS chainstays were typically a bit shorter than the Competition model. I see you've got the wheels all the way back in the dropouts. How much clearance do you have?

ehcoplex 

Well, as I said, as-bought it was pretty rough, and I discovered that the rear triangle was a bit 'out of whack', and I managed to convince myself the forks were ever so slightly bent backwards. So I decided it wasn't precious, and after muscling the rear end back into alignment I figured what the hell, and I dimpled the chain stays for more clearance- originally thinking if I could get 700x32 or maybe 35mm that would work for me. But I had the 650bx42 wheels on another bike, so put them on to see if they'd fit (my rebuild of the original wheels has proved to be problematic- getting them radially true with anything near consistent tension is beyond me- I suspect they may have had a close relationship to some serious potholes in the past...). It's pretty dang tight with the 42's- maybe 2.5mm clearance per side. I think I could do a little more dimpling for better clearance, or I may just go with 38s once I build up another set of 650b wheels with some Soma rims I've got on hand and call it a day. I'm pretty sure the bent forks notion was just in my head- the bike rides really nicely, tracks straight- might be the easiest to ride no-hands out of all I've got. Could partly just be a bit of woo-hoo, a 'new' bike to ride, but I think I really like it. It's also the biggest-framed bike I've ever had and I'm feeling like I've been riding too-small bikes all along..

nlerner

Nicely done! My very first 650b conversion was a Competition GS. I ran it with Col de la vie 38mm tires (this is before Hetres appeared, iirc) and a Campy NR rear mech shifting a 32t large rear cog! I had to remove the dropout adjusters and pull the wheel as far back as it could go. I’ll dig up some pics.

ehcoplex 

Did you have to use a hanger extender to get the NR to clear the 32t cog?

This drivetrain (temporarily borrowed from my Holdsworth), 46/42 x 13-32, I can just get away with in my steep and hilly terrain, though there are a couple particularly tough climbs I avoid. I've got a 49D compact double I might try, once I figure out (and find..) the right BB spindle for it, but then I lose the 1/2-step gearing I really love. I've also been oogling the Stronglight Tevano triple- a nice looking Campy knock-off that seems easier to find in a triple than an actual Campy triple... If the right rings existed for the Gran Sport three-arm crank, I'd consider drilling & tapping to make it a triple (yeah, potentially risky, I know).

52telecaster

Nice build man! Been riding my Triumph Gran Course 650b conversion lately. (Raleigh Professional sort of). Anyway, quick geometry and 650b is a hoot. Who knew 67 year old kids could have this much fun!

nlerner

Nope, no extender:



And the whole bike:



How about a half-step plus granny with that Stronglight 49D crankset? Of course, you'll still need to track down the right spindle (or use a cartridge BB).

ehcoplex 

Very likely what will happen. I’m kinda playing musical chairs, component-wise, with a couple in-process builds..