symptoms of worn chain rings

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hamishm
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symptoms of worn chain rings

Postby hamishm » Wed Aug 09, 2017 10:17 pm

I've had some trouble with the chain not landing on the small ring when changing from the big, when in the middle of the cluster (or smaller). It sorts of lands in between and slips along while the cranks are rotated. Switching to a bigger cog helps.

It got much worse with a new chain, so it must be worn chainrings, right? I just swapped those and on the workstand it looks fine now. Every time I've worn out chainrings before the symptom has been slipping under load, so this one is new to me.

I've actually had this problem for quite a while, but the chain would drop in eventually. Until the other day I'd never noticed it was the chain, always thought it was the freewheel on my cheap rear hub being slow to engage. Oops.

Specs are: Shimano 6770 FD, 6750 chain rings.

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Duck!
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Re: symptoms of worn chain rings

Postby Duck! » Thu Aug 10, 2017 7:51 pm

Poor shifting and chain drop are typical symptoms of worn rings.
I had a thought, but it got run over as it crossed my mind.

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Nate
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Re: symptoms of worn chain rings

Postby Nate » Fri Aug 18, 2017 6:01 pm

i have the same issue...
Newer shimano by any chance?
They actually increased the space between the rings to allow more cross chaining! (?!??!)

I also did the dodge & run a 39/50 setup - put a 50 ring on a non-compact.
I ended up gluing some bits of aluminium strip to make sure it doesnt slip between the cogs - worked a treat.

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hamishm
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Re: symptoms of worn chain rings

Postby hamishm » Fri Aug 18, 2017 6:52 pm

No more trouble with the chain dropping between rings after changing them. Just plain old Shimano 6750 here, no ghetto setups :-)

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hamishm
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Re: symptoms of worn chain rings

Postby hamishm » Thu Dec 07, 2017 10:20 am

Followup question about another bike:

My trainer bike won't shift from the small to the big ring under any load (it's ok on the workstand). The chain just slips around the big ring and never grabs on the teeth. This would be the big ring that's worn I assume? Can't find an affordable new crankset quickly so I'm hoping one of my old big rings might be an improvement at least.

Last time I changed rings (a different bike), it was the large to small shift that was terrible, would that be a worn small ring?

headasunder
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Re: symptoms of worn chain rings

Postby headasunder » Thu Dec 07, 2017 3:51 pm

hamishm wrote:Followup question about another bike:

My trainer bike won't shift from the small to the big ring under any load (it's ok on the workstand). The chain just slips around the big ring and never grabs on the teeth. This would be the big ring that's worn I assume? Can't find an affordable new crankset quickly so I'm hoping one of my old big rings might be an improvement at least.

Last time I changed rings (a different bike), it was the large to small shift that was terrible, would that be a worn small ring?


Before you change the big ring out put half a turn on the barrel adjuster and maybe allow a bit more leeway with your limit screw, I've had dropped chains and slippage caused by worn rings but shifting to the big ring has never been a problem so it may just be an adjustment issue

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antigee
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Re: symptoms of worn chain rings

Postby antigee » Thu Dec 07, 2017 3:56 pm

hamishm wrote:Followup question about another bike:

My trainer bike won't shift from the small to the big ring under any load (it's ok on the workstand). The chain just slips around the big ring and never grabs on the teeth. This would be the big ring that's worn I assume? Can't find an affordable new crankset quickly so I'm hoping one of my old big rings might be an improvement at least.

Last time I changed rings (a different bike), it was the large to small shift that was terrible, would that be a worn small ring?


cut down on the training a bit should even it out and save money? :)

sure someone that really knows more will be along shortly but for worn chainrings i usually look for hooking on the teeth and gouged ramps
small to big I'd check chain stretch if not already done and ring looks ok

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hamishm
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Re: symptoms of worn chain rings

Postby hamishm » Thu Dec 07, 2017 7:43 pm

Right well putting a different (but also not new) chainring on didn't help. I only thought this might be relevant because the problem seem to start when I changed to a brand new chain recently.

Anyway, changed the cables and sprayed a healthy amount of oil (and WD40) around the FD springs and cleaned up the BB cable guide.. all seems a lot better now.

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Duck!
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Re: symptoms of worn chain rings

Postby Duck! » Thu Dec 07, 2017 8:12 pm

While you're poking around the FD area, check the cage for bending or cracking. Some Shimano models have a long history of breaking the little bridge across the front of the FD cage.
I had a thought, but it got run over as it crossed my mind.

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CKinnard
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Re: symptoms of worn chain rings

Postby CKinnard » Thu Dec 07, 2017 8:37 pm

I said recently elsewhere that if you can set your gear changes up nicely in the stand, but they don't change smoothly when you sit on the bike, then one answer is a cracked frame. Or if you are very heavy, you may be flexing the frame excessively.

BTW, I've never worn out chainrings. I put 40,000km on my last bike, and the ultegra compact 6750 groupset still worked perfectly.

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Duck!
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Re: symptoms of worn chain rings

Postby Duck! » Thu Dec 07, 2017 9:21 pm

Chainrings do wear out, but they're the longest-lived drivetrain bits by a big margin. When in good nick, chainring teeth will typically have a rounded profile, but that will vary a bit depending on manufacturer; SRAM are typically more pointed than Shimano. Big rings can be difficult to assess to the untrained eye, because they have some very complex tooth contouring, and different tooth heights at shifting points, and can look "worn" even when new. Look around the ring, you'll see repeated patterns of tooth differences at several points.

Clues to look for to determine a worn ring are flattening of the troughs between the teeth; as the teeth wear the pitch length will effectively get longer. The teeth will wear on the leading edge, which is what causes the flattening of the troughs, and as the chain wears it will tend to sit up on the tops of the teeth, which will cause a characteristic "shark fin" profile.
I had a thought, but it got run over as it crossed my mind.

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Re: symptoms of worn chain rings

Postby Comedian » Fri Dec 08, 2017 7:38 am

hamishm wrote:Right well putting a different (but also not new) chainring on didn't help. I only thought this might be relevant because the problem seem to start when I changed to a brand new chain recently.

Anyway, changed the cables and sprayed a healthy amount of oil (and WD40) around the FD springs and cleaned up the BB cable guide.. all seems a lot better now.


I wonder whether it wasn't just releasing everything and checking tensions/limits etc. All sorts of things wearing, stretching, and even changing with temperature can cause things to not be perfect.

I guess that's why people like electronic because once set up it shouldn't change. I kind of like having the odd tinker with my bikes so as to keep them running 100% perfect.

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