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Old 01-11-10, 08:22 PM   #1
DavidG
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Problems with my Chainring Shimano Biopace SG.

Hello,
I have an old Giant Terrago and few weeks ago I started to have problems with the middle chainring.Some of the chainring teeth are very worn out and the chain skips.
The chainring that I have is a Shimano Biopace SG 48B/38/28 and unfortunately we don't have any bicycle repair shops in the Turks & Caicos Islands and I don't know what to do.
I know they don't make the Shimano Biopace SG anymore but what will be the best option for replacing this one?
Thanks for all your help
David
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Old 01-11-10, 08:41 PM   #2
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It depends on the bolt circle diameter of your crank. You can substitute any round chainring for the worn Biopace ring as long as the BCD is the same. You might find NOS Biopace rings on E-bay but round rings are far more common.
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Old 01-11-10, 08:48 PM   #3
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Hi HillRider,
Thanks for your reply.
Do you think it will be easier to replace the the three chainrings with a newer model instead of trying to find and old version of the Shimano Biopace SG?
Thanks
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Old 01-11-10, 08:58 PM   #4
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Hi HillRider,
Thanks for your reply.
Do you think it will be easier to replace the the three chainrings with a newer model instead of trying to find and old version of the Shimano Biopace SG?
Thanks
Wtf?
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Old 01-11-10, 09:01 PM   #5
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It would most likely be easiest to either call shimano or look up what kind spline your bottom bracket is. Either square or diamond would be my guess. From there grab a replacement crank set. As for which one, just match how many teeth your crank currently has as close as possible so that it will be a close replacement in gearing and fit your front derailleur. From there you should also replace your chain and rear cassette/freewheel. All the parts of a drivetrain stretch together and if it is stretched enough that it is slipping on your crank, most likely the rest is pretty bad. It is good practice to replace the chain and cassette/freewheel together and the crank when needed. Finally, if you do decide to use my suggestion you will need a crank puller to get the cranks off. A simple little tool that makes your life ten times better!
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Old 01-11-10, 09:08 PM   #6
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Thanks for your advice Zoodude.
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Old 01-11-10, 09:10 PM   #7
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It would most likely be easiest to either call shimano or look up what kind spline your bottom bracket is. Either square or diamond would be my guess. From there grab a replacement crank set. As for which one, just match how many teeth your crank currently has as close as possible so that it will be a close replacement in gearing and fit your front derailleur. From there you should also replace your chain and rear cassette/freewheel. All the parts of a drivetrain stretch together and if it is stretched enough that it is slipping on your crank, most likely the rest is pretty bad. It is good practice to replace the chain and cassette/freewheel together and the crank when needed. Finally, if you do decide to use my suggestion you will need a crank puller to get the cranks off. A simple little tool that makes your life ten times better!
Diamond? They made a diamond-shaped bottom bracket? Why wasn't I told?

He wants to replace the rings, not the crank.
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Old 01-11-10, 09:40 PM   #8
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I had the same issue a couple weeks ago -- the worn teeth on the middle BioPace were really getting to be a problem.
Though I usually pinch pennies until they turn into copper wire, I actually sprung for a whole new crankset. It was time for an overhaul of the bottom bracket so I just had whole thing done at once -- new crankset, chain, and rear cogset.
OMG, it's like riding a whole new bike, and the whole project was less than $150.
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Old 01-12-10, 12:38 AM   #9
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Find a replacement triple MTB crank and install it. That will probably be easier than finding just a middle chainring. Biopace just means the chainrings are slightly elliptical, but if you replace the whole crankset from another MTB, you won't have to worry about that. Triple cranksets are on pretty much every MTB made, so this shouldn't be TOO tricky to find, although you may need to pull the bottom bracket as well, to make sure everything lines up.

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unfortunately we don't have any bicycle repair shops in the Turks & Caicos Islands and I don't know what to do.
Do you think the Turks and Caicos could support a bike shop? Owning a combination beach bar / bike shop in the islands sounds like it might be the greatest thing in the world.
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Old 01-12-10, 12:59 AM   #10
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If you don't have ready access to a good used bike shop, or better yet, a bicycle co-op where you can root through a box of parts to take what you want, it's often cheaper and easier to simply replace the whole crankset in one go.

If you happen upon a middle chainring, don't worry about it being biopace. Round and Biopace chainrings can play together just fine. I have a Biopace inner ring with two outer round ones, and no trouble at all. As long as the BCD matches, and the tooth count is close you are good to go.
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