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Old 08-09-06, 07:02 AM   #1
wroomwroomoops
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How to tell if chainrings need replacing?

I have this old MTB in heavy need of fixing in various places. Now, to save a bit of money,k I was thinking that I might keep the chainrings, expecially since I can't seem to find 5-bolt MTB chainrings anywhere, so I would have to replace the crankset, too. But looking at the chainrings, I can't make up my mind if the chainrings are worn or not. They are, a bit, I guess, but are they functionally affected? Will they cause chainsuck once I replace the chain? (if it helps, I could post a piccy of the chainrings).

I have to mention that my eyes are not excellent, so my visual inspection may not be very effective. Still, whatever practical tip you have, I would be thankful.
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Old 08-09-06, 07:23 AM   #2
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first of all, 5 bolt chainrings might not be sitting around in you local performance bike shop, but good shops should have them in stock, as they are still made, in a decent variety. shimano even makes some. however there are two different bolt circle diameters for 5 bolt rings, so make sure you have shop check it out and indentify which size you need. a good way to tell if your rings are totally trashed: shift into the biggest chainring, and pull up on the chain with your fingers, trying to expose a chainring tooth. if you can, your chain is so trashed that is has definately trashed your rings to the extent that they all need replacing. if you cant expose a tooth, maybe just replace the granny gear, always a good idea. if you have an older crank, and friction shifting, i would recommend a SRAM pc 48 chain (16 bucks) and sugino rings, if you have a 110 BCD. a shop will know what that is. if you have the infinately more worthless (not your fault) 94 bcd, you should just get some LX rings, or deore if they are still made. same chain. its a good chain. now, once you have all that stuff, lube it all with prolink regularly, and you'll get maybe 10000 miles out of the drive train. sram makes good cheap cassettes too, 8 or seven speed.
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Old 08-09-06, 07:43 AM   #3
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If the teeth look like sharks fins (concave on one side) and if a new chain makes a rattling noise noise at the chainrings, then they are bad.

They can take lots of abuse so try a new chain first.
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Old 08-09-06, 07:55 AM   #4
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thanks, guys, for the advices!


Quote:
Originally Posted by San Rensho
If the teeth look like sharks fins (concave on one side) and if a new chain makes a rattling noise noise at the chainrings, then they are bad.

They can take lots of abuse so try a new chain first.
I'll do what you say, in about an hour, and let's see...

Quote:
Originally Posted by ridelugs
first of all, 5 bolt chainrings might not be sitting around in you local performance bike shop, but good shops should have them in stock, as they are still made, in a decent variety. shimano even makes some. however there are two different bolt circle diameters for 5 bolt rings, so make sure you have shop check it out and indentify which size you need. a good way to tell if your rings are totally trashed: shift into the biggest chainring, and pull up on the chain with your fingers, trying to expose a chainring tooth. if you can, your chain is so trashed that is has definately trashed your rings to the extent that they all need replacing. if you cant expose a tooth, maybe just replace the granny gear, always a good idea. if you have an older crank, and friction shifting, i would recommend a SRAM pc 48 chain (16 bucks) and sugino rings, if you have a 110 BCD. a shop will know what that is. if you have the infinately more worthless (not your fault) 94 bcd, you should just get some LX rings, or deore if they are still made. same chain. its a good chain. now, once you have all that stuff, lube it all with prolink regularly, and you'll get maybe 10000 miles out of the drive train. sram makes good cheap cassettes too, 8 or seven speed.
Are you sure about the availability of chainrings? This is a MTB, not a roadie - for road bikes, I know you can find plenty of 5 bolt chainrings, but not so for MTB. I have been looking around, and a new crankset with chainrings seems to not cost too much - as long as I am happy with a Deore set. Which I am.

I do have, by chance, an SRAM PC 48, ordered it 2 weeks ago, and it was in the mail yesterday. I also have a Suntour megarange 7sp cassette that I will install. the bike is indexed shifting.


Really, what is a 94 bcd, and a 100 bcd?
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Old 08-09-06, 08:04 AM   #5
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BCD is the bolt circle diameter. It's measured in milimeters.
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Old 08-09-06, 08:16 AM   #6
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Quote:
Originally Posted by wroomwroomoops
Are you sure about the availability of chainrings? This is a MTB, not a roadie - for road bikes, I know you can find plenty of 5 bolt chainrings, but not so for MTB. I have been looking around, and a new crankset with chainrings seems to not cost too much - as long as I am happy with a Deore set. Which I am.

I do have, by chance, an SRAM PC 48, ordered it 2 weeks ago, and it was in the mail yesterday. I also have a Suntour megarange 7sp cassette that I will install. the bike is indexed shifting.


Really, what is a 94 bcd, and a 100 bcd?
Yes, chainrings for a 5-bolt pattern, both sizes, are easy to come by. All my old school MTBs have a 110 BCD crankset on them. My 93 Giant just got a new outer ring for its Altus A10 crank. I used a Surly ring which isn't ramped or pinned, but still works. Cost=$38. Not to shabby. In the catalog at my LBS ther were plenty of others to choose from. Most mail-order companies have only the latest model parts for sale ie 4-bolt cranksets. A good shop can get older style parts easily from one of their numerous suppliers


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Old 08-09-06, 10:52 AM   #7
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what would the difference be between a road chain ring and a mountain chainring? if the bcd and bolt pattern is the same who cares about the moutain or road designation? Or is there some other difference?
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Old 08-09-06, 12:09 PM   #8
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The BCD is generally different.

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Old 08-09-06, 12:46 PM   #9
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Discussion on BCD here: http://www.sheldonbrown.com/gloss_bo-z.html#bcd

Good teeth:



Bad teeth:

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Old 08-09-06, 03:15 PM   #10
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Those are some great pictures. Thanks a bunch!

OK, well, my chainrings are somewhere inbetween those - maybe a bit closer to the "good" picture, except that some of the teeth are shorter, here and there. The granny ring is in very good condition.

Oh well - no new chainrings for a while. I am not anymore even sure I want to replace the cassette.
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