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Campy Gran Sport 3-arm crankset demystification

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Campy Gran Sport 3-arm crankset demystification

Old 01-20-24, 01:23 PM
  #26  
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Originally Posted by ehcoplex
Zombie revival! There's a pretty nice looking Raleigh Competition GS for sale not too far from me. My size, looks like it's in good shape, etc etc etc. Considering it has got me diving into the ins and outs of the Campy GS group. I wondered if anyone ever actually did try drilling the arms of a GS 3-arm crank to 'triplize' it with a small RH 3-bolt ring, as suggested above? Seemed like a kind of cool/interesting idea. I really like the way these 3-arm cranks look, but 42/52 doesn't really work for me where I live. I do have a Cyclotourist compact double laying around, but why do the easy thing?
Here's one I did in about 1979, using a 27t TA ring as the granny.


I managed to break one of the spider arms, but it didn't have anything to do with the conversion, it broke nowhere near where I drilled it for the granny ring bolt. And I was abusing it horribly at the time. I converted my 1933 Excelsior to a Marin County-style klunker with derailers, drum brakes etc, and used it for Observed Trials. Worst Trials bike ever, but I had fun, riding over giant fallen trees, picnic tables etc. until I made my custom trials bike in '81. I smashed it into a rock or something, I forget the details, bent the outer chainring something terrible and cracked the one spider arm that's pointing down in the pic. The break is near the base of the spider where it joins the crank It was a "displaced fracture", but I bent it back to where it looks like a little crack, but I wouldn't trust it for riding.

The Raleigh you're looking at has the alloy version of the crank, correct? Aluminum is weaker, but IIRC there's more of it, so my guess is it'll be strong enough for road riding. Just don't hop over picnic tables on it.

As you can see, I counterbored the holes so the heads of the "nuts" sit flush. This isn't necessary and I removed more steel from the spider arm that way, so it would have been stronger if I hadn't. Since your alloy crank doesn't have "windows" there, you can probably forego the nuts altogether, and just tap threads in the spider, for screws (M6 or larger) that come in from the back.

Campy's granny adaptor bolts use an M6 thread but there are 5 of 'em, so you might want to up that to M7 or M8 for a three-arm. I have no way to calculate what strength is needed, I'd just have to try it and see. Err on the side of larger bolts if you're risk-averse.
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Old 01-20-24, 01:31 PM
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You could also make a triple adaptor, like this one from jackbombay :



From this thread here. I vaguely recall he put it on an early-'70s Super Course.

Last edited by bulgie; 01-20-24 at 01:36 PM.
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Old 01-20-24, 01:44 PM
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Boy, do I love this forum! Thanks bulgie !

Yeah, it's a '78 or '79 Comp GS, alloy crank. Certainly putting the cart before the horse here, as I don't have the bike, and I'm not 100% sure I'll end up with it. I don't need it, but, well, y'know... But if..., it would be dang cool to have a triplized GS crank on it!
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Old 01-20-24, 06:31 PM
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Haven't considered it, but I have one and separated the 42 and 52 rings. I need to think about the granny option. Andrew Horsfall (sooner will know him from CR) is trying to convince me to ride Eroica in October. I would need lower gearing to get up some of the hills. Such a conversation might work. 🤔
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Old 01-20-24, 07:53 PM
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I have this crankset on two of my bikes. One came on my Raleigh Competition GS and I removed the chain guard . Then a couple years later a nice set became available on the bay for a super deal and I bought it for another bike . It came with an extra 53 teeth chain ring . They are both dated 1977 and 1978 . I really like that they are different from my other bikes with NR 5 pin. I am pretty sure you could get a smaller low ring on the crank but then there may be an issue with the chain wrap on the rear derailleur. I took the RD off my GS and replaced it with a NR unit after the cage came loose on the original . I was able to repair the derailleur but I never put it back on the bike after riding it with a NR . The Competition GS is a fun bike , I have had it for about 8 years now.
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Old 01-20-24, 08:13 PM
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Also keep in mind these are 116 BCD so you can use any old Simplex, TA, Stronglight, Magistroni, etc rings for a great sympathetic, place holder, upgrade, etc.

I used some Magistroni rings till I found a proper Stronglight Competition on the 58 Paramount.


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Old 01-21-24, 04:24 AM
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Old 01-21-24, 04:58 AM
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Originally Posted by Kabuki12
I am pretty sure you could get a smaller low ring on the crank but then there may be an issue with the chain wrap on the rear derailleur. I took the RD off my GS and replaced it with a NR unit after the cage came loose on the original. I was able to repair the derailleur but I never put it back on the bike after riding it with a NR . The Competition GS is a fun bike. I have had it for about 8 years now.
As I recall from my days using Nuovo and Super Record rear derailleurs, when the chain was long enough to accommodate the large-large combination safely, there'd be some significant amount of slack in the small-small combination, but that slack, though unsightly, never caused any problems.
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Old 01-22-24, 06:20 AM
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Originally Posted by Trakhak
As I recall from my days using Nuovo and Super Record rear derailleurs, when the chain was long enough to accommodate the large-large combination safely, there'd be some significant amount of slack in the small-small combination, but that slack, though unsightly, never caused any problems.
Take care of the big-big, and the small-small will take care of itself. Usually.
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Old 01-23-24, 06:31 PM
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I picked up this crankarm with a bunch of other Campy bits, unfortunately no NDS arm. It has an interesting chain guard.

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Old 01-24-24, 08:05 AM
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Originally Posted by VtwinVince
I picked up this crankarm with a bunch of other Campy bits, unfortunately no NDS arm. It has an interesting chain guard.
I have that same guard, in chrome-plated aluminium (or perhaps some zinc-Al alloy).
The plating is all peeling off.
Has yours also and then been painted?
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Old 01-24-24, 11:10 AM
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Looks like mine has the original finish, no evidence of respraying..
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