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Old 03-27-16, 12:29 PM   #1
hannathing
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Damage to chainring

I was cleaning my bike yesterday, as I had been riding in the wet and had kicked up loads of sand. As I was cleaning, I noticed a number of the teeth of the largest chainring were broken/worn down. There were a significant number of teeth that were rounded off. This is pretty surprising to me, as my bike is roughly 2 months old. Though, I have put roughly 350 miles on it already. I have an appointment scheduled with the LBS I bought it from, as they give a free check-up and tune-up for all new bikes.

Is there something I'm doing wrong? What could be causing it? How can I prevent it?
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Old 03-27-16, 12:42 PM   #2
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It doesn't make much sense to me. I know some mtb riders grind over logs and sometimes the big ring might bite into them, but even that shouldn't do too much damage as I understand it.
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Old 03-27-16, 12:42 PM   #3
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You may be mistaking engineered changes to speed the shifting from 1 chainring to another ..

The designed ones come at a point where the pedals are at Bottom center on each side , so 180 apart on the chainring.

then again do you have to drag your bike up Concrete stairways ?

Bash guard rings are made for intentional thrashing.
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Old 03-27-16, 01:35 PM   #4
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Over the last decade or so there has been an introduction of engineered sprocket teeth to help aid with shifting, and perhaps also prevent chain suck.

So, a NEW sprocket will have a few short teeth (almost appearing broken), and the back side of the teeth may be rounded while the pulling side is square.

Post some photos of your sprockets, but it is possible they are NORMAL.

Beware of stretched chains, but 350 miles is short for that too.
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Old 03-27-16, 01:46 PM   #5
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Maybe I'm being dramatic. There looks to be some wear and tear, but I'm not sure how extensive it really is.



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Old 03-27-16, 01:53 PM   #6
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I don't see anything particularly concerning about the tooth profiles.
The short tooth in the middle of the 2nd photo is right next to a shifting ramp, and was there from the factory.

As you pedal, the chain pulls to the right end of the channel, or the left side of the tooth (from the view of the photos). Any rounding to the back side of the teeth (right side of the tooth, left of channel) would be by design and not affect your riding.
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Old 03-27-16, 05:54 PM   #7
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There's no way the chainrings could wear out in two months. Your chainrings look normal. Some of the teeth are shorter than the others to aid in shifting.
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Old 03-27-16, 06:36 PM   #8
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I agree with the above, although some of the finish has worn off, the tooth profile looks like a design feature rather than wear-and-tear. Is the chain slipping or anything?
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Old 03-27-16, 07:29 PM   #9
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Dirty, slightly worn, not damaged.
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Old 03-28-16, 05:49 PM   #10
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I've been having some shifting issues, but not between the front gears. I'm taking the baby in this week for the free check-up and cleaning. The roads here are over salted and then covered in sand in the winters, so my ride to and from work is pretty grimy. I need to do a better job on keeping the gears/chain clean.

Thanks for the help! It's good to know I was freaking out over nothing
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Old 03-28-16, 10:06 PM   #11
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You're far from the first person to look at those nubby gear teeth and get worried.
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Old 03-28-16, 10:17 PM   #12
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Thanks for the help! It's good to know I was freaking out over nothing
Hint.

As long as you can clearly tell the difference between the "normal" and "sculpted teeth on the ring, it's fine. It's when all the teeth look pretty similar that you need to worry.
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Old 03-29-16, 08:13 AM   #13
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Quote:
Originally Posted by hannathing View Post
I've been having some shifting issues, but not between the front gears. I'm taking the baby in this week for the free check-up and cleaning. The roads here are over salted and then covered in sand in the winters, so my ride to and from work is pretty grimy. I need to do a better job on keeping the gears/chain clean.

Thanks for the help! It's good to know I was freaking out over nothing
I had those worries when I first started riding. I mean, you put down some good money you want your bike to work well! Your shifting issues are probably just rear derailleur cable stretch (also something I was concerned about at about 250-300 miles)...a few quarter turns with the barrel adjuster will have you sorted right out. Definitely nothing to worry about there.
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Old 03-29-16, 08:44 AM   #14
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If you look at your bike's cassette in the rear, you'll see a similar thing. You will also see ramps cut into the side of the cogs or rings. If you put the bike up into a stand and turn the pedals very slowly while shifting the gears, you will notice the chain only shifts at these ramped portions. Not only that, the chain can physically engage both the cog or chainring it is shifting off of, and the cog or chainring it is shifting onto. These features are why drivetrains shift so quietly. It also allows for less finessing; you don't have to "soft pedal" nearly as much when changing gears compared to pre-CAD drivetrains.
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Old 03-29-16, 02:23 PM   #15
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@bmthom.gis quarter turn which direction?

I am asking for a friend
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Old 03-29-16, 03:04 PM   #16
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@bmthom.gis quarter turn which direction?

I am asking for a friend
Tell your friend that it's in the direction that works. Follow the logic below, and pass it along so your friend understands the concept.

>>>>Turning the barrel in the direction that screws it outward, (counter-clockwise, looking from the top) lengthens the housing, which has the same effect as shortening the wire, and moves the derailleur inward.

>>>>Turning it so it screws inward, does the opposite and moves the RD outward.

Adjust the RD trim in the direction that solves your problem, ie. inward for crisper shifting to larger sprockets, outward for crisper upshifting to smaller ones, looking for the most neutral balance between the two.

Assuming all was correct, and you suspect cable "stretch" that would have moved the trim outward (the same way as shortening the housing) so bring the adjuster out to correct.

If your friend simply remembers that the adjuster changes the housing length, which is exactly opposite to changing wire length he'll never go wrong.
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