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When to replace chain rings?

Old 07-25-16, 05:48 PM
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dmanthree
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When to replace chain rings?

I've been trying to find a creaking noise that seems to be coming from the bottom bracket area, and I was wondering if there's some rule of thumb when it comes to replacing chain rings. My front shifts aren't as quick and positive as they used to be, and the large chain ring teeth seems to be slightly resembling hooks. Could this be the cause of the creaking It happens on both chain rings and only when I'm standing on the pedals.

I'll look at the BB, as well. I'm curious; how can I tell if I have a threaded or press-fit BB? It's a 2012 Madone 5.2.
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Old 07-25-16, 09:54 PM
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Threaded BB, on a bike as new as yours will have external cups with indentations like these (the indentations are for the tool you use to install or remove). They'll be very similar in appearance no matter what brand of crank you have:



Older threaded BBs don't look like that but your 2012 Trek will.

Press fit BBs don't have external cups that can take the tool like that.

Hope that makes sense.

As for the chain wheel question, I'll let others answer that.
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Old 07-25-16, 10:08 PM
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I would have thought Trek was using BB90 by 2012.
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Old 07-26-16, 06:00 AM
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YMMV but my general rule is replace two chains, on 3d chain the cassette will be worn and not mesh, so replace. On 4 th chain a CW
replacement is likely because of CW/chain not meshing. Creaks in the BB can be elusive. The cartridge BB (pictured by Camilo)
are cheap and easy to replace. Pressed in bearings require a little more finesse to R&R. And replacing the BB may not solve the
creak. Also look at pedal to crank and crank to axle threadings. Sometimes an apparent BB creak is actually the seat post/saddle
area.
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Old 07-26-16, 06:20 PM
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Originally Posted by 2lo8 View Post
I would have thought Trek was using BB90 by 2012.
The spec sheet says BB90, so is that pressed fit?
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Old 07-26-16, 09:33 PM
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Park tool on BB90 (press fit BB): Bottom Bracket Service: BB90, BB86, BB92, GXP Press Fit | Park Tool
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Old 07-26-16, 09:44 PM
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This one creaked on my bike.

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Old 07-28-16, 02:27 PM
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Originally Posted by dmanthree View Post
I was wondering if there's some rule of thumb when it comes to replacing chain rings.
Chain on big ring...at 3 o'clock pull the chain away from the ring. If you can see daylight between the tip of the tooth and the chain then the chain ring is whipped.
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Old 07-29-16, 09:30 AM
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How often do you replace your chain?

The more the chain is stretched and used in that state, the quicker the teeth will wear. I once bought a used bike that needed a new chain. I replaced the chain and found the cassette was pooched. So then I replaced the cassette and once that was grabbing hold well the chain rings couldn't handle it and I nearly ended up on the top tube the first ride out. In the end I had a new drivetrain.
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Old 07-29-16, 09:58 AM
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Chain rings need to be repaced when they become shark-teethed - no longer round along the top.
If you regularly replace your chain, which is usually cheaper, you can get 15 years from your alloy chainrings.
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Old 07-31-16, 06:37 PM
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The teeth on the big ring are a little shark-toothed. I replace the chain annually, and I've got about 23,000 miles on the chain rings. I spend about 70% of my time on the big ring. I think I'll replace it. Cheap enough.
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Old 08-01-16, 08:07 PM
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Originally Posted by dmanthree View Post
The teeth on the big ring are a little shark-toothed. I replace the chain annually, and I've got about 23,000 miles on the chain rings. I spend about 70% of my time on the big ring. I think I'll replace it. Cheap enough.
Get out your camera and post a pic already.
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