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Old 05-12-11, 10:25 PM   #1
thook
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Granny gear for Stronglight cottered crank: Where to find/what to use?

Hey all,

I've got this SL cottered crank and a beat up Nervar cottered crank. The Nervar chainrings are bent to hell, but the outer 52t ring has the bolt holes in the middle for a granny. If I cut the section out of the Nervar ring with those bolt holes, I could straighten it out (or try to ) and fit it to the SL between the outer and inner ring in place of the spacers. Of course, I'd need to add an extra, thin washer for each bolt to get the spacing correct. But, if I can get this work out, I'd need to source a granny gear to fit. I don't even know the BCD for it, yet. I'm guessing in the 50mm/something range by eye ball. Anyway, modern rings.....if I could even find one with the same BCD.... have too large of bolts holes. So, I figure that's out of the question. I considered butchering a junk, one piece crank for it's "granny" by drilling out the rivets and then drilling holes to suit the triplizer, but that would be kinda ugly and not even sure if I could get spacing correct with it being offset towards the inside by design.( I hope you all understand what I mean by "offset") I'd rather just find a ring that would actually fit, though......and look good.

If anyone's got suggestions, that'd be great.

Oh, also.......this SL crank is going on my mid 70's Dawes galaxy. It's the original crank and the chrome is still in great shape.....amazingly. The original derailleurs are the Prestige variety and....well....toast. I tried to salvage one out of a couple I had, but the plastic broke. So, on the rear, I want to use a Huret Duopar and the front I'm considering using an Allvit I already have. Not the prettiest thing, but it's steel and won't break...haha! BUT!! Will it handle a triple, is the question???? If not, maybe if I modify the adjustment/limit stops...ie, grind them down a bit???? Or, would it be rather an issue of the "arms" being able to reach in length??

Thanks!
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Old 05-13-11, 09:03 AM   #2
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bttt............
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Old 05-13-11, 12:56 PM   #3
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A picture is worth a couple of hundred words as is an accurate BCD measurement.

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Old 05-15-11, 09:27 AM   #4
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I'll have to see if I can find a pic on the web, then. And, bcd....well, I'll see about getting that, too. I was just hoping someone in the C&V world might be familiar enough with these old, French cottered cranks I could get away with just describing.

Okay......thanks!
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Old 05-15-11, 10:44 AM   #5
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Sheldon has a way to measure BCD on 3 bolt cranks.
I took the big sprocket off of a dead freewheel for mine. I've since picked up a shiny cassette sprocket with 6 arms to replace it with. I haven't had time to do the drilling yet so you'll have to imagine how cool this will look.
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Old 05-15-11, 12:01 PM   #6
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thook, did you see this thread of mine? Not exactly the same problem... but called for a somewhat similar solution.

I didn't want to use a steel ring for this, because it'll rust. Stainless might be nice, but isn't available. I don't suppose you can find an aluminum chain ring the right size? A TA ring, with six spokes, might be perfect for this purpose.

But as others have said, a picture would be worth something or other. I can't quite picture what you're trying to do.

There was a thread about 3-pin steel cottered cranks a few weeks ago; and someone posted a very useful table of BCD's. You might want to find that....
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Old 05-15-11, 03:08 PM   #7
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Sheldon has a way to measure BCD on 3 bolt cranks.
I took the big sprocket off of a dead freewheel for mine. I've since picked up a shiny cassette sprocket with 6 arms to replace it with. I haven't had time to do the drilling yet so you'll have to imagine how cool this will look.
http://i291.photobucket.com/albums/l...qoLJNmw_35.jpg[/IMG]
Yep......that's what I'm lookin' to do. Maybe I can find a cassette cog cheap enough on ebay. Otherwise, they're like $35, right?
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Old 05-15-11, 04:40 PM   #8
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I got this one for about $15. Don't know what they'd cost new. I tried the LBS to see if they had any orphans but no luck.
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Old 05-15-11, 08:55 PM   #9
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thook, did you see this thread of mine? Not exactly the same problem... but called for a somewhat similar solution.

I didn't want to use a steel ring for this, because it'll rust. Stainless might be nice, but isn't available. I don't suppose you can find an aluminum chain ring the right size? A TA ring, with six spokes, might be perfect for this purpose.

But as others have said, a picture would be worth something or other. I can't quite picture what you're trying to do.

There was a thread about 3-pin steel cottered cranks a few weeks ago; and someone posted a very useful table of BCD's. You might want to find that....
Well, hopefully this'll help matters.......

Here's a pic of a Nervar very similar to the one I have that's all messed up...



Now, imagine three "spider arms" extending from the outer chainring towards the center of the actual crank spider. In the center, the "spider arms" connect to a small circle of five holes.....of unknown BCD, at this point. I'll look into that table, though.

Anyway, see where the outer chainring bolts to the crank arm spider? Well, the toothed, outer area of the outer ring is waaay bent out of shape. But, the "spider arms" coming from the outer ring are not so bent and good be straighten on a flat concrete shop floor or shop table with a flat head hammer........I figure, anyway. So, my idea is to cut the "spider arms" away from the outer toothed portion leaving the bolt holes intact. Then, with it flattened, it could bolted to the inside of the spider on this Stronlight crank in place of the original spacers that are between the spider and inner 42t ring. Spacing adjusted, of course, with enough thin washers.

Does this help?

The cassette cog looks VERY promising, though. Thanks, sailorbenjamin, for that idea. In fact, the more solid, center area of that cog in your picture looks (and I would imagine) to be an appropriate enough size to fit this Nervar triplizer ring. One question.....what brand/kind of cassette cog is that? It doesn't appear to have Hyperglide ramped teeth.

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Old 05-15-11, 09:06 PM   #10
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Sheldon has a way to measure BCD on 3 bolt cranks.
I took the big sprocket off of a dead freewheel for mine. I've since picked up a shiny cassette sprocket with 6 arms to replace it with. I haven't had time to do the drilling yet so you'll have to imagine how cool this will look.
Uh.....hold the wagon! Lemme get this straight.....and, this may make things a whole hella lot easier for me. You simply just bolted that freewheel cog to the crank spider, didn't you?? And, is that what you intend to do with that cassette cog, as well? If that's the case, I don't even have to mess with this whole Nervar triplizer thing. Hmmmm...........
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Old 05-15-11, 09:13 PM   #11
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Oh, wait........nevermind. This Stronglight has a larger, three bolt BCD than that crank in your pic. Right......that's why I need to use the triplizer....duh, duh, duh!

Here's a pic of the exact SL crank I have.......


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Old 05-15-11, 10:39 PM   #12
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Ah-ha!!!!!!!!!!!!!!!! Here's more or less what the triplizer looks like......



Except, in my case with the Nervar crank, it is part of the outer chainring........as I've said.

'Nuther question............do you any of you gents know if this Simplex ring........



.......will mate to the outer ring of a Stronglight crank as the one pictured above? You know, on those outer 6 bolt holes????
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Old 05-16-11, 06:29 AM   #13
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Ah-ha!!!!!!!!!!!!!!!! Here's more or less what the triplizer looks like......

I suppose it might be possible to use it as triplizer, but that's not what that is. That Simplex adapter is for mounting 3-pin chain rings to a 5-pin 50.4 mm BCD ring.

I think the easiest (and perhaps only) solution for you will be to find a freewheel cog like the one Ben showed a couple posts back; drill three holes in that and three holes directly in the arms of your crank; and mount it with a bunch of spacers.
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Old 05-16-11, 09:14 AM   #14
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Do you mean it's meant for adapting a 3-pin ring to a 5-pin crank spider? Like a TA crank or something??? And, why wouldn't it work as a triplizer? Do you think it'd be too flimsy to support the low end torque??

Well, regardless, I think you're idea is much easier. I'd thought of doing that originally anyway, but was reluctant to drill into the crank spider and mess up the chrome finish. But, engh.....so what...ha! It's only where the holes'll be.

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Old 05-16-11, 09:36 AM   #15
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Do you mean it's meant for adapting a 3-pin ring to a 5-pin crank spider? Like a TA crank or something???
Right, exactly that.
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And, why wouldn't it work as a triplizer? Do you think it'd be too flimsy to support the low end torque??
No, I'm sure it'll support the torque okay. I'm more concerned about spacing; this has an offset between the three bolts and the five, and if it's too much, I'm not sure there's anything you can do about it. It probably isn't, though, so you'll probably be okay. My main hesitation, though, is that you just don't need it. If you can drill a hole in each of the arms of your crank and three matching holes in a freewheel cog, you have all the room you need. Conventional triple crank spacers may be all you need to get the spacing right.

Is your concern that your crank is too precious to drill holes in the arms? I respect that. Still, I think I'd rather do that than buy the Simplex thing on ebay, where it'll cost as much as a whole new old cottered crank.
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Old 05-16-11, 09:40 AM   #16
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I got this one for about $15. Don't know what they'd cost new. I tried the LBS to see if they had any orphans but no luck.
So, where'd you get that one and what brand is it?? It doesn't look Shimano .....having no ramped teeth.
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Old 05-16-11, 09:48 AM   #17
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Right, exactly that. No, I'm sure it'll support the torque okay. I'm more concerned about spacing; this has an offset between the three bolts and the five, and if it's too much, I'm not sure there's anything you can do about it. It probably isn't, though, so you'll probably be okay. My main hesitation, though, is that you just don't need it. If you can drill a hole in each of the arms of your crank and three matching holes in a freewheel cog, you have all the room you need. Conventional triple crank spacers may be all you need to get the spacing right.

Is your concern that your crank is too precious to drill holes in the arms? I respect that. Still, I think I'd rather do that than buy the Simplex thing on ebay, where it'll cost as much as a whole new old cottered crank.
Oh, no way I was thinking of buying that doo-dad. I mean, I already have one..... I was just using that pic as a reference for you all.

Precious??? Yes and no. If I didn't have to drill it, I didn't want to. But, in the end, I just need a granny and the crank was free to me. So, no big thing overall. I'll just drill it and it'll be done with it.

Well, that was easy. Thanks, gentlemen.

Oh, about that Simplex 48t ring, though. Any idea if it'll mate to the Stronglight outer ring? I looked a bunch over the internet and couldn't find any info. Maybe I'm just not using the right keywords, but I'm tired of reading through non-pertinent info....haha!

So you know, I'm wondering about that Simplex 48t because it'll make a nice half step mated to the SL 52t. That with a 28t granny and I'll be quite pleased.
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Old 05-16-11, 10:02 AM   #18
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So you know, I'm wondering about that Simplex 48t because it'll make a nice half step mated to the SL 52t. That with a 28t granny and I'll be quite pleased.
Ah, hmm, I see. Yeah, it looks like it might; but I don't know and can't tell from the photos. Do you have a source for the Simplex ring? Measure --or ask someone to measure-- the distance between two holes. Compare to your Stronglight. Voila.
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Old 05-16-11, 10:11 AM   #19
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Ah, hmm, I see. Yeah, it looks like it might; but I don't know and can't tell from the photos. Do you have a source for the Simplex ring? Measure --or ask someone to measure-- the distance between two holes. Compare to your Stronglight. Voila.
Right.....of course. So, what.....just ask the seller to measure the distance between one bolt hole to the adjacent one? If it matches my Stronglight, I'm good to go, right?
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Old 05-16-11, 10:15 AM   #20
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The 48t ring has a BCD of 157mm. I guess I need to measure my SL ring. And, how to do that is on Sheldon's site, right?
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Old 05-16-11, 05:26 PM   #21
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Here's the Sheldon link;
http://sheldonbrown.com/gloss_bo-z.html#bcd
That cog isn't actually the one I ended up buying. It's just a stock picture that I stole so that I'd have something to show people when I asked for one. I ended up buying an actual hyperglide.
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Old 05-17-11, 05:23 PM   #22
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I see. I like how the one looks in your picture with the six "arms" and all. I'll look for something like that.......unless I just wind up using a cog off of an old freewheel.

Thanks for the link!!!!!!!
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