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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 10-04-10, 12:27 PM   #1
illdthedj
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3 bolt chainring questions....

i posted this in the vintage forum, but i thought i would give it a shot here:

I am in the middle of rebuilding an old 79 Raleigh Mixte frame for my girlfriend.
It has a cottered crankset, with 3-bolt type spider and chainring. The BCD i believe is 106....basically 101mm from bolt to bolt.

Now, The two chainrings it came with are a 40 tooth and 49 tooth (or was it 50? anyway)
I am converting the back hub to a simple coaster brake (ease of use for her, she is used to it and likes it)....

ANYWAY, to my questions:
i really would like to find a 3 bolt chainring with anywhere between 42 to 44 teeth, most preferential is 43. I have found some on ebay, mostly from one seller, but they arn't super cheap and the seller has basically ignored the 3 emails ive asked about the BCD of the chainrings. I dont feel like buying and hoping they will fit.

ok, questions:
1) does anyone know about typical BCDs for 3 bolt cranksets? IE....were there a ton of varying BCDs, or just a few common ones....on ebay i saw an 85mm BCD chainring, and i think mine is 106 (or at least going by sheldon brown's calculation, 101mm x 1.1155)

i ask because this one chainring this non-communicative seller has LOOKS like the correct size, but if i hear from someone here "oh yah theres basically only 2 main 3 bolt chainring BCDs" then i might pull the trigger....

2) does anyone know of some online store or something that i just cant find thru google searching that would have a selection of 3 bolt chainrings?


ANY help is GREATLY APPRECIATED!!!
thanks!
dan
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Old 10-04-10, 01:14 PM   #2
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I'd replace the entire bottom bracket and crank set. I had cottered cranks and they are a serious pain in the ass. Not to mention 3 bolt chainrings are terrible (at least in my past experiences.)
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Old 10-04-10, 01:39 PM   #3
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Hey Dan. Your formula is incorrect, and for a 3 pin crank it should be BCD = 1.15 x BHC, so if your BHC (bolt hole center to hole center) is 101mm, then you have a 116mm bcd crank. A 106 BCD crank will have a 92mm BHC. What is the brand of your crank? Most European cottered cranks like Nervar, Solida, Simplex, Gnutti etc are 116 BCD, whereas Japanese like Sakae, Takagi and Sugino are 106 BCD. Hope this helps.

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Old 10-04-10, 02:36 PM   #4
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eek, you are correct, i do have a 116 bcd NOT a 106 bcd....
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Old 10-04-10, 02:58 PM   #5
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thanks tejano!

and well, i might as well ask while im here:
i see a 3 bolt chainring from a seller on ebay, and although they dont list the BCD, they say "10 cm hole to hole".....im ASSUMING they are talking about a 116 BCD, which is 10.1 CM.......is that a safe assumption? they dont make 115 BCDs do they? and if they did, would a 1 mm bolt to bolt really make a difference? im assuming they just quickly measured it and it looked like a square 10 cm to them....
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Old 10-04-10, 03:01 PM   #6
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Originally Posted by YaBoiHeSoFresh View Post
I'd replace the entire bottom bracket and crank set. I had cottered cranks and they are a serious pain in the ass. Not to mention 3 bolt chainrings are terrible (at least in my past experiences.)
i WOULD replace the entire bottom bracket and crankset, BUT this is for a somewhat low-budget beat-around-town coaster brake bike for my GF.
i attempted to remove the cottered cranks, and tried hammering the cottered pins out, but even with some lubricant and some solid hits with a hammer, they wont budge. Also, i dont feel like paying money for an appropriate drill or paying the LBS to remove, on top of replacing the bottom bracket and cranket (more $$$) especially when the bottom bracket seems to spin decently and the crankarms/spider seem fine.
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Old 10-04-10, 04:32 PM   #7
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Originally Posted by illdthedj View Post
i see a 3 bolt chainring from a seller on ebay, and although they dont list the BCD, they say "10 cm hole to hole".....im ASSUMING they are talking about a 116 BCD, which is 10.1 CM.......is that a safe assumption? they dont make 115 BCDs do they? and if they did, would a 1 mm bolt to bolt really make a difference? im assuming they just quickly measured it and it looked like a square 10 cm to them....
Yes, it's almost certainly meant for a 116mm bcd 3-pin crank spider, and no there is no such thing as 115 bcd. Am I to assume you are looking at one of these listings?

http://cgi.ebay.com/NOS-VINTAGE-STEE...item20aabaeff7

The seller is located in France, so you may have a long wait to get it. Actually, I was thinking of getting one of these for my conversion, but really don't want to spend the money, since it's a pretty cheap low end bike and I'd rather spend it on other better projects.
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Old 10-04-10, 05:42 PM   #8
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Yes, it's almost certainly meant for a 116mm bcd 3-pin crank spider, and no there is no such thing as 115 bcd. Am I to assume you are looking at one of these listings?

http://cgi.ebay.com/NOS-VINTAGE-STEE...item20aabaeff7

The seller is located in France, so you may have a long wait to get it. Actually, I was thinking of getting one of these for my conversion, but really don't want to spend the money, since it's a pretty cheap low end bike and I'd rather spend it on other better projects.
ha, you are exactly right sir in your assumption. i only bought one because in another listing they specifically say "10 cm from bolt to bolt".....and yes expensive, but i had a bunch of ebay dollars saved up (about 20 something) so it wasn't nearly as expensive.
i DIDN"T want to buy from them, because i did notice they were located in France, also because i emailed them a number of times asking about BCDs on other chainrings without any sort of answer for days.

BUT after searching a bunch on ebay and elsewhere, it seemed to be my only option for a 3 bolt 116 BCD chainring.

basically i want my girlfriend's bike to have an optimal gear ratio. the double chainring that came on the crankset was 40 teeth and 50, and with a 16 t and 18 t coaster brake cog none of the gear ratios seemed appropriate....40t /16t would still be a little low, plus the skid patches (its a coaster brake bike and im sure she is going to be skidding here and there) are only 2 on that ratio. 50t/18t has 9 skid patches but seemed a little high. 46t/18t is i think a good ratio for her, so the 46t chainring i think will work out well. i guess i was previously looking for 42t-44t chainrings, but in retrospect i think that might be too low. i dont want it to be tough for her, but i also want her to be able to keep up with me.....
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Old 10-04-10, 06:46 PM   #9
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Quote:
Originally Posted by illdthedj View Post
does anyone know about typical BCDs for 3 bolt cranksets? IE....were there a ton of varying BCDs, or just a few common ones....on ebay i saw an 85mm BCD chainring, and i think mine is 106 (or at least going by sheldon brown's calculation, 101mm x 1.1155)

i ask because this one chainring this non-communicative seller has LOOKS like the correct size, but if i hear from someone here "oh yah theres basically only 2 main 3 bolt chainring BCDs" then i might pull the trigger...
Not millions, but at least 8 fairly popular BCDs:
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Old 10-04-10, 06:56 PM   #10
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^^^ ref. Southerland's Handbook for Bicycle Mechanics, Third Edition, page 2-5.
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Old 10-04-10, 07:02 PM   #11
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i WOULD replace the entire bottom bracket and crankset, BUT this is for a somewhat low-budget beat-around-town coaster brake bike for my GF.
i attempted to remove the cottered cranks, and tried hammering the cottered pins out, but even with some lubricant and some solid hits with a hammer, they wont budge. Also, i dont feel like paying money for an appropriate drill or paying the LBS to remove, on top of replacing the bottom bracket and cranket (more $$$) especially when the bottom bracket seems to spin decently and the crankarms/spider seem fine.
Same problem here. Finally had to drill the ENTIRE cotter pin out. I was pretty unlucky, my crank arm and chainring were moving independently, and were completely shot.
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Old 10-04-10, 09:58 PM   #12
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Same problem here. Finally had to drill the ENTIRE cotter pin out. I was pretty unlucky, my crank arm and chainring were moving independently, and were completely shot.
yah i REALLY debated doing exactly that. because i was in the middle of a stripping of the parts to rattlecan the frame. but i thought "well, do i buy a decent drill, drill out the pins, then buy a new bottom bracket and crankset, or do i just leave it be since it seems to spin alright (for now) and just plastic bag the crankarms before spraypainting"

and i did the later. was a ***** to spraypaint around the crankarms, but overall i think buying a random hard to find chainring for 30 bucks and taking time to wrap and tape crankarms took less time and money than the aforementioned.

basically down the line, if the GF is getting more and more into biking with me (which is the plan and which she seems to be into) and the bottom bracket or crankset seems to give her functional bike riding problems then its time to drill those damn cottered pins out and upgrade to a nice square taper BB.
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Old 10-04-10, 10:01 PM   #13
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oh and this is bike in question, in case anyone cares lol


yah right now you see the 40 t ring on there. i assume a low gear would be nice for her to start with but 40t/16t is kind of ridiculously low.
so once i get that 46t 3 bolt ring in, it will be 46t/18t. still low, but not roadrunner-legs fast-spinning low
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Old 10-04-10, 10:03 PM   #14
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Not millions, but at least 8 fairly popular BCDs:
this is exactly what i was looking for earler, thanks!
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Old 10-05-10, 08:19 AM   #15
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the double chainring that came on the crankset was 40 teeth and 50, and with a 16 t and 18 t coaster brake cog none of the gear ratios seemed appropriate....40t /16t would still be a little low, plus the skid patches (its a coaster brake bike and im sure she is going to be skidding here and there) are only 2 on that ratio. 50t/18t has 9 skid patches but seemed a little high. 46t/18t is i think a good ratio for her, so the 46t chainring i think will work out well.
With a 28mm tire, 40-16 is 66.9 GI. 46-18 is 68.4 GI. I doubt she could even tell the difference of 1.5 GI.

Skid spots don't matter on a coaster brake. You may get some from the pawls on the hub, but the wheel is independent of the cranks so the ratio doesn't matter.

Save your money, and use 40-16.
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Old 10-05-10, 02:27 PM   #16
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wow, we're building a very similar bike for similar situations..

i'm rebuilding a '76(?) Raleigh Grand Prix that was previously converted to single speed. It has a cottered crank and a 3 bolt ring. Running coaster brakes. AND its for my girl.

My problem started when i was riding it around town, stopped at a light and was standing on the pedals when the ****in chainring just crumples up into a taco...i think this is where the 3 bolt has its limitations. Its just not strong enough.

Every shop i have visited has simply said to change out the whole BB setup, new ring, new cranks, etc....So that's what i'm doing.

Looking for a new crankset, then i'll find the appropriate BB.

good luck man, keep us updated. and nice bike! paint it yourself?
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Old 10-05-10, 02:38 PM   #17
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My problem started when i was riding it around town, stopped at a light and was standing on the pedals when the ****in chainring just crumples up into a taco...i think this is where the 3 bolt has its limitations. Its just not strong enough.
It depends on the design of the chainring. The one on my conversion is pretty beefy, and hasn't given me any problems.
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Old 10-05-10, 03:34 PM   #18
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wow, we're building a very similar bike for similar situations..

i'm rebuilding a '76(?) Raleigh Grand Prix that was previously converted to single speed. It has a cottered crank and a 3 bolt ring. Running coaster brakes. AND its for my girl.

My problem started when i was riding it around town, stopped at a light and was standing on the pedals when the ****in chainring just crumples up into a taco...i think this is where the 3 bolt has its limitations. Its just not strong enough.

Every shop i have visited has simply said to change out the whole BB setup, new ring, new cranks, etc....So that's what i'm doing.

Looking for a new crankset, then i'll find the appropriate BB.

good luck man, keep us updated. and nice bike! paint it yourself?
wow crazy! hmmm well ill probably keep my 200+ pound ass off her bike lol, perhaps it will be OK for her since she weighs allot less. of course the second the bottom bracket or crankset gives her problems is the second i shell out the dough to replace them for more traditional (and easier to work on) components.

mind posting pics of the ride you are making for your girl? and let me know what BB works for your raleigh, i think it might be safe to say ours use the same kind (both being late 70s models).....good luck getting those cottered cranks off! those pins are a B!!!TCH to get out. i tried and just ended up mushrooming the pin (at least it wont be coming out while shes riding).....im definitely going to have to drill them out if i want to replace them.

and yup i painted it myself! rattlecan job....got some mean chemical paint stripper, sanded the rest, did about 2 cans worth/ 3 coats of everything, then 2 coats of clear finish. although there are some patchy areas.....i totally made sure to cover the frame everywhere with clearcoat, but i think the brand i got was crap and came out a little uneven....only really noticeable if are really looking closely. probably get another can of clearcoat and finish it off down the line. not too worried about it, techinically this was supposed to be a beater bike lol but its shaping up to be a little nicer than i thought.

anywho keep in touch!
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Old 10-05-10, 08:52 PM   #19
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Don't mind me, just checkin' in to see where this bike is going. Could use more tarck, but I like her.
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Old 10-06-10, 12:00 AM   #20
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Many older bikes used cottered cranks that were of very good quality with nice forgings and good quality pins but latter day models with cotter cranks tended to be lower end and entry level models and may have been fitted with lesser cranks and chain rings.

A few folks have asked me why I haven't replaced the cottered track crank on my 1955 Raleigh with something lighter and "better"...

IIRC Raleigh stopped using cottered cranks in 1978 except on three speed models and if you have cottered cranks you are probably going to have to deal with a 26 tpi bottom bracket that is also wider than normal.
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Old 10-07-10, 03:13 PM   #21
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Don't mind me, just checkin' in to see where this bike is going. Could use more tarck, but I like her.
*CROSSPOST ALERT WHOOP WHOOP WHOOP*



havn't done much, but greased up and installed headset, stem, handlebars, cut them, hairsprayed the oury's on, put the seat post on, oh and the front fender lol

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still have to install back coaster cog, back fender, seat and peddles when they come in the mail....and pink chain lol
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