Knackered chainrings?

[straas]

Stuck a new chain on and doesn't seem to skip at all, but only did a lap of the block.

Better image of the chainring attached.

 

[Yellow Saddle]

OK, that photo reveals a lot more.

The area I circled in red is the powerstroke area from your right leg.
The area in green is the dead zone.

Have a look how much more the teeth are worn in the red area than green.

The shape of worn teeth represent shark fins (not shark teeth as often quoted, because shark teeth are symmetrical and chainring tooth wear is asymmetrical) with the sharp end pointing forward.

The is because the chain pulls on the teeth and wears pockets into the leading edge, eventually creating an area that's hollowed out, hence the shark fin shape that points forward.

What happens under these conditions is that the chain defaults to a position on the chainring that's not centre on the teeth but pulled back, with the centre of the chain bushing slightly behind the centre point of the tooth.

Eventually, this causes the new incoming tooth (as the ring rotates) to hit the next available bushing, instead of missing it. This creates a specific noise and a vibration. Both will be noticeable only to the mechanically sympathetic, mechanical-minded person.

It is time to replace your chainring.

 

[C R]

OK, that photo reveals a lot more.

The area I circled in red is the powerstroke area from your right leg.
The area in green is the dead zone.

Have a look how much more the teeth are worn in the red area than green.

View attachment 507989

The shape of worn teeth represent shark fins (not shark teeth as often quoted, because shark teeth are symmetrical and chainring tooth wear is asymmetrical) with the sharp end pointing forward.

The is because the chain pulls on the teeth and wears pockets into the leading edge, eventually creating an area that's hollowed out, hence the shark fin shape that points forward.

What happens under these conditions is that the chain defaults to a position on the chainring that's not centre on the teeth but pulled back, with the centre of the chain bushing slightly behind the centre point of the tooth.

Eventually, this causes the new incoming tooth (as the ring rotates) to hit the next available bushing, instead of missing it. This creates a specific noise and a vibration. Both will be noticeable only to the mechanically sympathetic, mechanical-minded person.

It is time to replace your chainring.

In a situation like this, would rotating the chainring in the spider so that the worn area sits where your green circle is make sense, or is the chainring too far gone.

 

[straas]

OK, that photo reveals a lot more.

The area I circled in red is the powerstroke area from your right leg.
The area in green is the dead zone.

Have a look how much more the teeth are worn in the red area than green.

View attachment 507989

The shape of worn teeth represent shark fins (not shark teeth as often quoted, because shark teeth are symmetrical and chainring tooth wear is asymmetrical) with the sharp end pointing forward.

The is because the chain pulls on the teeth and wears pockets into the leading edge, eventually creating an area that's hollowed out, hence the shark fin shape that points forward.

What happens under these conditions is that the chain defaults to a position on the chainring that's not centre on the teeth but pulled back, with the centre of the chain bushing slightly behind the centre point of the tooth.

Eventually, this causes the new incoming tooth (as the ring rotates) to hit the next available bushing, instead of missing it. This creates a specific noise and a vibration. Both will be noticeable only to the mechanically sympathetic, mechanical-minded person.

It is time to replace your chainring.

Thanks for a very in depth explanation! I'll get a new one on order, I think my list is:

1 X 50t chainring
1x 32t 11sp cassette
1 X 11sp chain
2 X jockey wheels

Current plan is to ride it as is until it starts to skip, then change the lot. Sound sensible?

 

[Yellow Saddle]

Thanks for a very in depth explanation! I'll get a new one on order, I think my list is:

1 X 50t chainring
1x 32t 11sp cassette
1 X 11sp chain
2 X jockey wheels

Current plan is to ride it as is until it starts to skip, then change the lot. Sound sensible?

Chainrings don't skip, unless the teeth are all completely gone. The front and back react completely differently to chain wear. As I said, the front's symptoms are a noisy, vibrating pedal action.
In the rear it won't skate (let's use skate, rather than skip because skip refers to gear indexing problems) either, until you fit a new chain, which will then be mismatched with the sprocket.

There's is plenty of good explanations on here, do a search for...perhaps "skate" and "worn sprocket" etc.

 

[Yellow Saddle]

In a situation like this, would rotating the chainring in the spider so that the worn area sits where your green circle is make sense, or is the chainring too far gone.

In theory, yes.
There is a caveat or two though. Some chainrings are now matched to crank in a 3D way, so offset is not possible and/or not aesthetic.
Secondly, there's a pin embedded in the chainring that prevents the chain from falling between the crank and the spider. Should that pin now go where it can't do it's job, a chain that came off is a ride-stopping event. A chain jams extremely tightly into that V space. You will have to carry your bike home.
Thirdly, the shifting will be slightly iffy because the ring has specially-positioned ramps and pins that make the chain shift in special places, such as when you can't power the drivetrain because the pedals are in the 12 and 6 o clock positions etc. However, this can be overcome and is no big deal.

Chainrings will missing teeth still work perfectly provided you don't shift on the missing tooth. There is plenty of "wrap" to not even notice it.

 

[PpPete]

Chainrings don't skip, unless the teeth are all completely gone. The front and back react completely differently to chain wear. As I said, the front's symptoms are a noisy, vibrating pedal action.
In the rear it won't skate (let's use skate, rather than skip because skip refers to gear indexing problems) either, until you fit a new chain, which will then be mismatched with the sprocket.

Not my experience:
I have known a chain "skate" or "skip" on a badly worn chainring - but only under load and it was perfect smooth and quiet running the rest of the time ... and the rear shifting was perfectly OK because chain and cassette had worn together.

 

[Yellow Saddle]

Not my experience:
I have known a chain "skate" or "skip" on a badly worn chainring - but only under load and it was perfect smooth and quiet running the rest of the time ... and the rear shifting was perfectly OK because chain and cassette had worn together.

The fact that it was quiet running means that it went way past the first stage of wear and you simply didn't even notice that it was running noisy and vibrating.
Here's stage one, when you should replace the chainring.

Notice the tips pointing forward. Rotation is obviously clockwise. Here the tips are hitting incoming rollers and making a noise and vibrating the chain as it hits - slips past the tooth.

Here's stage two. If you hit this, don't give up your day job as opera singer, you're useless at mechanical things and should not be let loose on a bicycle. However, it can get worse than this even, but I can't find my photo of that one right now.
Notice that all the tips which used to hit the rollers, have now worn away.

At stage three there's just a smattering of teeth left and the bike makes ZRRRRT when pedalled.

 

[Ajax Bay]

The area I circled in red is the powerstroke area from your right leg.
The area in green is the dead zone.
Have a look how much more the teeth are worn in the red area than green.

But isn't the set of teeth you've circled in green the 'powerstroke area from your left leg' and why would there be a different level of tooth wear between the peak torque from one side cf the other?

 

[Yellow Saddle]

But isn't the set of teeth you've circled in green the 'powerstroke area from your left leg' and why would there be a different level of tooth wear between the peak torque from one side cf the other?

Sharp. I attached a saved draft instead of the final one. The draft was a .png but saved a final jpg and I selected the wrong one.
Here's the right one. Red for right leg, green for dead (but overlapping with left leg I now see), and orange for left leg.

The photo isn't great, but you may notice that the right leg is stronger than the left. I often see this. The accumulated wear and the average thereof displays strength discrepancies nicely.

 

[straas]

Struggling to find an 11pd 50t chainring that looks similar to what's currently on there.

Will I encounter issues with a 10sp chainring? not sure what the differences will be? (if any)

https://www.wiggle.co.uk/shimano-105-fc5703-10-speed-triple-chanrings/

 

[straas]

For reference - if anyone stumbles across this thread and has an identical chainring:

Despite other components being marked shimano 105, this chainring is not (I assume to keep costs of the build down), so you want to look for:

Shimano FC-RS500 - in this case the variant is the 50t-MH, and annoyingly is quite expensive!

 

[boydj]

For reference - if anyone stumbles across this thread and has an identical chainring:

Despite other components being marked shimano 105, this chainring is not (I assume to keep costs of the build down), so you want to look for:

Shimano FC-RS500 - in this case the variant is the 50t-MH, and annoyingly is quite expensive!

No need to buy a Shimano replacement. A compatible replacement from someone like Spa Cycles will be much cheaper.

 

[Tom B]

After reading this thread decided to have a look at the clunker.

I think I spot a bit of wear.

Rear mech is currently hanging off due to a broken hanger hence the jaunty chain angle. And front mech has been mangled for a while but still works.