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cottered crank chainring question

Old 07-01-22, 11:08 AM
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cottered crank chainring question


back side

i'm considering this MAGISTRONI Cottered 3 arm crankset on ebay and it is in need of an inner chainring. i'm not at all versed in what fits what for vintage cottered cranksets, so if i wanted to find myself something like a 44 or 42 tooth ring, does it need to be a 6 bolt or 3 bolt? and what brands will fit? or to make my life even easier, does anyone have a chainring they might sell me?

Last edited by cocoabeachcrab; 07-01-22 at 12:47 PM. Reason: added some pics
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Old 07-01-22, 01:00 PM
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Many of those older cranks, including Magistroni, used common bolt circle diameters. The 3-bolt chairing with a 116 mm bcd was quite popular and was made by TA, Stronglight, Williams, Chater-Lea, Simplex, and probably others as well, and I suspect your crank might be an example. The smallest ring in that size is 36t, and steel rings are not too hard to find. Will you need longer bolts? The most common 6-bolt rings had bcd's of 80 mm, 116 mm, and 152 mm. I don't know what yours is, but for a 42t inner ring you'll probably want a 3-bolt model that attaches to the crank arms.

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Old 07-01-22, 01:08 PM
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I just measured a very similar Magistroni crank, and the three pins are 116 BCD; chainrings of that format are quite common, smallest being a 36. Your outer bolts I'm not sure of the BCD but if it's the same as the TA 3-6 pin adaptor - which it looks to be - the BCD is 152 and the smallest that'll fit is a 43.

Most likely the existing arrangement has a short sleeve projecting outwards from the crank arms, the chainring holes fit the sleeves, and the bolts thread into the sleeve and crank and hold the ring on. If so fitting the 36 will require some longer bolts, spacers, and nuts. Fitting a ring to the six-bolt pattern (which will work with only three bolts, some only have three holes) might also need different bolts/spacers/nuts, though the ones shown look so loose that you may be lucky to find them long enough, at least..
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Old 07-01-22, 01:09 PM
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Originally Posted by kroozer View Post
Many of those older cranks, including Magistroni, used common bolt circle diameters. The 3-bolt chairing with a 116 mm bcd was quite popular and was made by TA, Stronglight, Williams, Chater-Lea, Simplex, and probably others as well, and I suspect your crank might be an example. The smallest ring in that size is 36t, and steel rings are not too hard to find. Will you need longer bolts? The most common 6-bolt rings had bcd's of 80 mm, 116 mm, and 152 mm. I don't know what yours is, but for a 42t inner ring you'll probably want a 3-bolt model that attaches to the crank arms.
perfect... thank you!
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Old 07-01-22, 01:23 PM
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p.s. I had a good look at that crank. It looks to me to have been re-chromed - the logo is part-polished away. The ring is a TA and it looks to have been polished as well - so much so that the teeth are rounded smooth where they should be square, tends to hide the worn profile.

Just me, but I'd be looking for something less shiny and less worn.
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Old 07-01-22, 01:28 PM
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Originally Posted by oneclick View Post
p.s. I had a good look at that crank. It looks to me to have been re-chromed - the logo is part-polished away. The ring is a TA and it looks to have been polished as well - so much so that the teeth are rounded smooth where they should be square, tends to hide the worn profile.

Just me, but I'd be looking for something less shiny and less worn.
i noticed that too. thanks
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Old 07-01-22, 01:37 PM
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I recently bought this Legnano pantographed crank, ring and bottom bracket set. The cranks are probably Magistroni and that means the rings will fit. The best way to ensure that is to measure the center to center distance between two spider holes. The picture below shows the NOS rings that I have no use for at this time...


Anyway, I did not use the original ring set, opting for Simplex instead...


That means that I have a NOS set of rings, big and small that should fit. If interested, measure the distance between holes (be precise), let me know and I will list the set of the for sale forum.
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Old 07-01-22, 01:41 PM
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cocoabeachcrab I may have something but it would need chainrings. I can check tonight if you are interested.
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Old 07-01-22, 01:44 PM
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Originally Posted by randyjawa View Post
I recently bought this Legnano pantographed crank, ring and bottom bracket set. The cranks are probably Magistroni and that means the rings will fit. The best way to ensure that is to measure the center to center distance between two spider holes. The picture below shows the NOS rings that I have no use for at this time...


Anyway, I did not use the original ring set, opting for Simplex instead...


That means that I have a NOS set of rings, big and small that should fit. If interested, measure the distance between holes (be precise), let me know and I will list the set of the for sale forum.
thanks, randy. i think i like to look of the simplex rings as well, so i think i'll be on the look out for a set.
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Old 07-01-22, 01:47 PM
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Originally Posted by RustyJames View Post
cocoabeachcrab I may have something but it would need chainrings. I can check tonight if you are interested.
yes i would! let me know what you have. i'm going to begin a search for a set of simplex chainrings.. i think they are the competition set.
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Old 07-01-22, 01:58 PM
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...there are some issues with different standards for the spindles (length and diameter) on cotter cranks, as well. I've not had many problems finding chainrings, because most of the double sets I've encountered fit the same BCD at the three arms of crank spider, itself. I have run into problems sourcing chainring bolts that will work, and the whole spindle and cotter fitting thing can be tedious.
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Old 07-01-22, 02:23 PM
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Just picked up a set that might be of interest. The chrome is not perfect but the spider and rings are Magistroni. They will clean up pretty good but not perfect. Bolts included if this is of interest. I also have a head badge, in case the OP needs one for his build...


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Old 07-01-22, 02:41 PM
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Originally Posted by randyjawa View Post
Just picked up a set that might be of interest. The chrome is not perfect but the spider and rings are Magistroni. They will clean up pretty good but not perfect. Bolts included if this is of interest. I also have a head badge, in case the OP needs one for his build...


those head badges are really great! thanks for that offer.. i have keep that in mind!
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Old 07-01-22, 03:56 PM
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Just a note - the six-hole patterns for the double chainsets are not always/often/ever equally-spaced, but the TA pattern is equal.
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Old 07-01-22, 04:42 PM
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Originally Posted by oneclick View Post
Just a note - the six-hole patterns for the double chainsets are not always/often/ever equally-spaced, but the TA pattern is equal.
??
The 6 bolts of the 3-piece Simplex 3-to-6 adaptor are evenly spaced. Minimum chainring size = 45T. Riveted system hanging the inner ring on the outer, using the same 6-bolt BCD (1952-3 Capo Sieger)


Simplex 3-to-6:

Almost all-orig. 1960 Capo Sieger That's a whopping 58T outer ring, 45T inner ring. I found a 49 to replace the outer with something rational.
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Old 07-01-22, 06:36 PM
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Originally Posted by John E View Post
??
The 6 bolts of the 3-piece Simplex 3-to-6 adaptor are evenly spaced.
Yes, but
a) they're french, even "not always/often/ever" still does not encompass all they might do; and
b) the Magistroni's aren't.
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