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Campy Gran Sport 3-arm crankset demystification

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Campy Gran Sport 3-arm crankset demystification

Old 06-05-17, 01:30 PM
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Campy Gran Sport 3-arm crankset demystification

I've never held one of these Tullioesque marvels in my hand--only seen pictures of them--so I found myself floundering a bit when someone asked me about them the other day. I'm hoping that someone with first-hand experience with them will be able to clear up some questions for me:

1. As far as I can see, the outer chainring is 116 BCD. On a double, the inner ring would ordinarily use the same BCD, and be held on by the same chainring bolts--with the outer ring on the outside of the crankarm spider, and the inner ring on the inside of the spider. But here, the inner ring evidently isn't bolted to the spider at all--it's bolted to a separate set of holes in the outer ring (presumably with 3 or 4mm spacers between the inner and outer rings). My guess, from looking at the photos, is that the inner ring is a 144 BCD ring. Therefore, the outer ring must be drilled with two sets of holes--one at 116, and the other at 144. Is that correct?

2. What's the point of all that? Why not just use 116 for both rings? Maybe the idea is that bolting the inner and out rings together with spacers stiffens the whole assemble, and reduces flex, given that the 116 bolt circle places the bolts pretty far from the teeth of the big ring? Or is it just gratuitous Campagnolan complexity?

3. What's up with the chainring bolts? They don't look like the standard chainring bolts with the 8mm allen-head bolt and 10mm slotted nut. Or could one use those standard bolts in place of the hex-headed ones in the photos?
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Old 06-05-17, 03:14 PM
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You'll probably have to find a medium to raise the spirit of Tullio in a seance to answer any of those questions...authoritatively...Jon.
Good luck.
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Old 06-05-17, 03:35 PM
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Unique. And as rootboy suggested, a seance is in order.
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Old 06-05-17, 03:57 PM
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At launch, model 3320/A had riveted c/w's with a dentition offering limited to 42/49, 42/50, 42/51, 42/52 & 42/53 (same as for Sport chainset Nr. 3320). Only the 170mm length was offered. Supplied with 9/16" pedal thread as standard and metric available as special order. Illustrated on page 59 of catalogue Nr. 17 (1974).

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Old 06-05-17, 06:43 PM
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I don't know but will speculate.

Gran Sport was a lower priced line, while (Nuovo) Record was the full price set. So while it behooves the manufacturer to offer a lower priced set, it would not be good if the cheap stuff were actually preferred.
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Old 06-05-17, 07:46 PM
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It follows the same practice as 3-bolt steel cranks, with only the outer ring (or the Simplex 3-to-6 adapter set) attaching to the spider, which is probably too thick for mounting one ring to the outside, the other to the inside.
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Old 06-05-17, 08:21 PM
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Originally Posted by John E
It follows the same practice as 3-bolt steel cranks, with only the outer ring (or the Simplex 3-to-6 adapter set) attaching to the spider, which is probably too thick for mounting one ring to the outside, the other to the inside.
That seems to be the issue--if you were to attach a 116 bcd ring in the inner position, the inner and outer rings would be so far apart (given the thickness of the "ring-contact zone" at the ends of the spider arms) that the chain would fall down between them if you tried to shift.

Bt if one were to mill the inner faces of the bolt-hole areas on the spider down to a thickness of 4mm or so, it would be possible to use rings as small as 35 or 36 teeth in the inner position. Wouldn't it? Or am I missing something?

Of course, that would go against my long-standing rule against permanently modifying old components. But I'd be tempted to make an exception in this case, since the modified version would be an objective improvement on the original design.
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Old 06-05-17, 08:36 PM
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Originally Posted by jonwvara
That seems to be the issue--if you were to attach a 116 bcd ring in the inner position, the inner and outer rings would be so far apart (given the thickness of the "ring-contact zone" at the ends of the spider arms) that the chain would fall down between them if you tried to shift.

Bt if one were to mill the inner faces of the bolt-hole areas on the spider down to a thickness of 4mm or so, it would be possible to use rings as small as 35 or 36 teeth in the inner position. Wouldn't it? Or am I missing something? ...
That should work, assuming sufficient strength in the milled-down spider ends. Another option is to use the common Simplex 3-to-6 bolt adapter triplet, but you can't go below 45 teeth with that.
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Old 06-06-17, 05:20 AM
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This 38T 116BCD Gran Sport chainring was outed in the thread on three-arm chainrings on CR:

https://www.ebay.com/itm/311827018216

With such a low tooth count, it has to be an inner (what ya gonna drill those 144 holes?), so while the setup Jon identified is probably the norm, the two-rings-same-BCD setup must have been possible. I can't imagine Campy would make rings for the competition's cranks.

I'm the guy who's been pestering Jon about these cranks, btw...
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Old 06-06-17, 05:53 AM
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I've often wondered if the 36 & 38T Gran Sport chainrings were used to create a triple. It looks like it could be done using the bolt kit for Campagnolo's standard triple conversion.
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Old 06-06-17, 12:10 PM
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Catalogue parts illustration for launch iteration of model 3320/A:
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Old 06-06-17, 12:26 PM
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^Looks like the chainrings came as a unit and weren't mean to be separated?
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Old 06-06-17, 01:04 PM
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Originally Posted by Reynolds
^Looks like the chainrings came as a unit and weren't mean to be separated?
Yes, in launch iteration. A carryover from the Sport model Nr. 3320. Not later.



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Old 06-06-17, 02:39 PM
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Originally Posted by smontanaro
This 38T 116BCD Gran Sport chainring was outed in the thread on three-arm chainrings on CR:

Campagnolo Gran Sport Chainring 3 Hole 38T Vintage Road Racing Bicycle NOS

With such a low tooth count, it has to be an inner (what ya gonna drill those 144 holes?), so while the setup Jon identified is probably the norm, the two-rings-same-BCD setup must have been possible. I can't imagine Campy would make rings for the competition's cranks.

I'm the guy who's been pestering Jon about these cranks, btw...

Yeah, Skip, this whole thread is your fault!

I still have no idea why Campagnolo made 36- and 38-tooth rings. Of course, you could use them as outer rings, but in the days before the singlespeed fad, who wanted a 36- or 38-tooth outer ring?

Possibly later versions of the crank were configured in the usual way, so the inner and outer ring sandwiched the ends of the crank spider, as in most cranks? As I speculated in post #7, you could presumably modify one of the 116/144 cranks to work like that. Maybe the design eventually got rationalized in just that way. That's a question for someone with free time and a complete set of 1970s Campagnolo catalogs.

If that wasn't the case, why the 36s and 38s? Inquiring minds want to know.


Originally Posted by T-Mar
I've often wondered if the 36 & 38T Gran Sport chainrings were used to create a triple. It looks like it could be done using the bolt kit for Campagnolo's standard triple conversion.
T-Mar, do you mean converting the standard double to a triple by way of a Bob-Freeman-style aftermarket drilling of the spider arms? It's hard to imagine that even Campagnolo would provide rings for that use without also offering factory-drilled cranks. (Maybe they did produce such a crank, but I've never heard of it.) In any case, a 36 or 38 seems pretty big for the granny ring of a triple.
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Old 06-06-17, 02:52 PM
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Originally Posted by jonwvara
T-Mar, do you mean converting the standard double to a triple by way of a Bob-Freeman-style aftermarket drilling of the spider arms? It's hard to imagine that even Campagnolo would provide rings for that use without also offering factory-drilled cranks. (Maybe they did produce such a crank, but I've never heard of it.) In any case, a 36 or 38 seems pretty big for the granny ring of a triple.
There would be no need to drill the spider arms. Since the BCD of this crankset is 116mm all you would need to create a triple is a 116mm BCD, three hole chainring of an appropriate tooth count (like 36T or 38T) and longer mounting hardware with an appropriate width spacer. It would be quite easy to make a 36/42/5xT combination.

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Old 06-06-17, 03:16 PM
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Originally Posted by T-Mar
There would be no need to drill the spider arms. Since the BCD of this crankset is 116mm all you would need to create a triple is a 116mm BCD, three hole chainring of an appropriate tooth count (like 36T or 38T) and longer mounting hardware with an appropriate width spacer. It would be quite easy to make a 36/42/5xT combination.
Ohhh....I get it now! (When we had moments like that in 9th grade math class, back in Massachusetts, our teacher, Mr. Daven--an Irish guy from the North Shore somewhere--used to say "Aha! Dawn breaks over Marblehead!")

So you'd have a 116 outer, a 144 middle, then back to a 116 for the inner! Right, it would just be a matter of coming up with the right spacers.

What my brain was hanging up on was that the notion that the middle ring would have to be 116, because...well, because who would go to a different BCD for the middle ring of a triple? I am evidently an inside-the-box thinker.

Thanks, T-Mar. You probably can't even see the box from where you do your thinking.
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Old 06-06-17, 05:15 PM
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Originally Posted by jonwvara
....Thanks, T-Mar. You probably can't even see the box from where you do your thinking.
There are no boxes here. There are no spheres here. It's just one huge Mobius strip. One instant, I'm inside. The next, I'm outside. Never ending, never ending....
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Old 06-06-17, 05:28 PM
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Originally Posted by jonwvara
So you'd have a 116 outer, a 144 middle, then back to a 116 for the inner! Right, it would just be a matter of coming up with the right spacers.
I still don't understand. How would you connect the inner 116 ring to the middle 144 ring? Can someone draw me a picture?
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Old 06-06-17, 07:13 PM
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Originally Posted by smontanaro
I still don't understand. How would you connect the inner 116 ring to the middle 144 ring? Can someone draw me a picture?

The 116mm inner ring would be completely independent of the 144 ring. You'd run one long bolt through the 116mm holes in the outer ring and the crankarm spider, with maybe 5 or 6 mm of the bolt extending beyond the inner surface of the crank spider (I'm guessing on length here--as I said, I've never even seen one of these cranks in three dimensions.) Then you put some spacers over the protruding portion of the bolt, put a small 116mm ring (like a 36-tooth, or maybe even 35) on top of the spacers, and tighten a nut onto the bolt. If the correct thickness of spacers is used, the inner ring will end up positioned about 4mm inboard of the middle ring. This could take a little trial and error, but shouldn't be hard.

Does that make sense?

Not sure what you'd use for nuts/bolts, since I don't know the dimensions of the bolt holes in the outer ring or crankarm spider. Assuming that they're the standard 10mm, maybe you could use those old-style chainring bolts that are meant to extend through all three chainrings, say on an 86 BCD triple. You might have to shorten the nut a little, though that again is a guess.
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Old 06-06-17, 08:13 PM
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^ Got it. That would explain why people over on the CR thread were referring to potential shifting issues when using the three-arm GS in a double configuration with both rings attached to the spider.

I just got off my butt and grabbed a pair of Campy drive-side arms from my parts bin, a NR and a GS three-arm. Where the chainrings bolt to the spider, the NR is 3.6mm thick with shelves inside and out. The GS is 4.6mm thick with a shelf on the outside, but not the inside. You could, in theory, mill 1mm off the inside bringing the dimensions into the same range as the NR, and creating a small inside shelf.


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Old 06-06-17, 08:36 PM
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One other question. If Campy intended for the outer ring to be a 116BCD bolted to the arm, with a 144BCD ring used as an inner, bolted to the outer chainring, what's the point of 116BCD? You won't be able to run an inner smaller than 41T.
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Old 06-07-17, 05:11 AM
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Originally Posted by smontanaro
One other question. If Campy intended for the outer ring to be a 116BCD bolted to the arm, with a 144BCD ring used as an inner, bolted to the outer chainring, what's the point of 116BCD? You won't be able to run an inner smaller than 41T.
I don't think we'll ever know that without, as someone mentioned earlier, conjuring up Tullio's ghost. The whole system seems kind of crazy to me. Although the crank does look kind of cool, in an odd way.

I was in touch with Bob Freeman the other day, and he thinks he could do a triple conversion by drilling the arms, similar to what he does with 144 BCD Record and NR cranks. The only issue is whether spreading the load over three drill holes rather than five would sacrifice too much strength. He expected to use a Compass chainring (from one of their three-arm Herse cranks) as a granny. They're available down to 24 teeth and have a 70mm BCD (if I remember that right), so the drill holes in the spider would be relatively near the base of the spider arms, where they're wider and presumably stronger.

I'm ordinarily one of those guys who will go to almost any length to avoid permanently modifying old components, but this crank is such a quirky bastard that I think I'd make an exception to that rule
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Old 06-08-17, 09:00 AM
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It's also possible that something like a 36T or 38T ring could have been used on a ladies' model. We've seen a few higher end, Italian female frames with SL tubing. They could have tried something like a 49/38T pairing using longer bolts and spacers. Or it could have been used as 38T single on a 5 speed ladies' city bicycle.

I also wouldn't rule out the possibility that these smaller chainrings were used on some youth category bicycles, where gearing was restricted.

If the chainrings were manufactured at the request of a specific customer or even samller volume, they would not necessarily have been catalogued. Or they could simply have been manufactured during years that fell between Camapgnolo's catalogues.
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Old 06-08-17, 10:49 AM
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Had a steel one, ala 13th post, sold it off, finally, last year..

3 arm 116 bolt circle crank arms, in Sutherlands, has a long list of companies in that type..

there was a 36, 52 pair..

Peugeots came with some, riveted together , steel.




....

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Old 01-20-24, 12:51 PM
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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?
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