cottered crank chainring question
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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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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.
Last edited by kroozer; 07-01-22 at 01:05 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..
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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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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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.
Just me, but I'd be looking for something less shiny and less worn.
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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.
Just me, but I'd be looking for something less shiny and less worn.
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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.
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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cocoabeachcrab I may have something but it would need chainrings. I can check tonight if you are interested.
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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.
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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cocoabeachcrab I may have something but it would need chainrings. I can check tonight if you are interested.
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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.
...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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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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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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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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Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
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"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069
Last edited by John E; 07-01-22 at 04:45 PM.