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Old 06-25-10, 10:51 AM   #1
Dougtron
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Help with 6-Bolt Chainring

I have a Crescent bike and recently the chainring got bent and I'm having a hard time find a replacement. It's a 45t but I'm having trouble measuring it because it's a 6 bolt chainring and I haven't really been able to find much information about them online. I measured from from the center of one hole to the center of the other and it was about 79 or 80 mm. Sorry I don't have a lot of info for you guys to go on but any help would be greatly appreciated.
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Old 06-25-10, 10:54 AM   #2
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6 bolts? interesting. can you tell us a bit more about the bike and cranks? about how old is the bike? do you know if the cranks are cottered style? a pic would be huge help.
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Old 06-25-10, 11:43 AM   #3
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6 bolts like this?

(mind the broken crank)
It has 6 holes on a 3 hole spider. (this crank has about 110mm BCD, just measured it)

Just measure between two opposed bolts to find the BCD.

Last edited by Asi; 06-25-10 at 11:47 AM.
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Old 06-25-10, 12:27 PM   #4
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Here's a picture of my crankset and the chainring. I bought the bike off of a friend but I believe it's from sometime in the 70's. Sorry about the really bad picture quality but the camera on my phone is all I have right now.
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File Type: jpg crank..jpg (10.2 KB, 22 views)
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Old 06-25-10, 01:14 PM   #5
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this is interesting setup. finding a replacement ring for that might be impossible. however if that is a regular Ashtabula type crank you should be able to remove the 'spider' and put a regular BNX style ring on there

http://www.sheldonbrown.com/opc.html

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Old 06-25-10, 02:02 PM   #6
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Thanks a lot! Now I'm having trouble removing the crank. It seems to be the standard type of crank you mentioned but there doesn't seem to be anything for me to unscrew to get it off. I've included a picture of the other side to show you what I mean. Thanks for all the help!
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Old 06-25-10, 05:38 PM   #7
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Here's a picture of my crankset and the chainring. I bought the bike off of a friend but I believe it's from sometime in the 70's. Sorry about the really bad picture quality but the camera on my phone is all I have right now.
Looks like the old Simplex bolt pattern (also used by Magistroni and others):


Alas, these are not very common anymore. You may find it easier to replace the entire crank/bottom bracket assembly. There are conversion kits that allow a standard bottom bracket to be installed in a frame designed for one-piece Ashtabula cranks; perhaps one of those would fit your Crescent?
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Old 06-25-10, 05:40 PM   #8
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Thanks a lot! Now I'm having trouble removing the crank. It seems to be the standard type of crank you mentioned but there doesn't seem to be anything for me to unscrew to get it off. I've included a picture of the other side to show you what I mean. Thanks for all the help!
Have you tried a pin spanner in those notches?
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Old 06-25-10, 07:18 PM   #9
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Have you tried a pin spanner in those notches?
Someone else told me that so now I just have to take it to a bike shop that has a pin spanner. Once I remove this crank what exactly would I need to do to install a modern crank set?
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Old 06-25-10, 07:22 PM   #10
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Someone else told me that so now I just have to take it to a bike shop that has a pin spanner. Once I remove this crank what exactly would I need to do to install a modern crank set?
You need a conversion kit, like the one shown half-way down the page.

http://www.sheldonbrown.com/harris/opc.html
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Old 06-25-10, 07:31 PM   #11
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Thanks for the help everyone! It seems though that they are selling single chainrings that look they would fit my crank. Before I bent my chainring I was using it as a single speed with a 45t chainring, and on the Sheldon Brown site they have 44t and 46t chainrings for a one piece crank like mine. So would you guys recommend getting a conversion kit and upgrading to a modern style crank set or would one of those chainrings work on my crank, and if so should I get the 44t or the 46t since they don't have a 45t chainring. Everyone here has been a major help to me, seeing as I'm just starting to get into working on bikes.
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Old 06-25-10, 08:56 PM   #12
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If you can find a replacement ring go for it. Bike probably isn't worth getting the conversion kit, new BB, & new cranks.

If you are still running it as a SS, the 44 will make it easier to pedal than the 45. The 46 will be harder to pedal than the 45. It is up to you.
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