Does this crankset look worn out?

[Jimmy Doug]

Thanks for all the feedback. I took the crankset to my lbs yesterday, and he basically confirmed what everyone here has said: it is slightly damaged but it shouldn't be so damaged as to wear out a chain. He did ask me if my chain was too slack - a question I found surprising because I didn't think a slack chain would cause premature chain wear. What do you guys say about this? In any case, I will change the crankset for a slightly better one - just to make sure.

 

[mickle]

... He did ask me if my chain was too slack ....

Walk away and don't look back, he's obviously an idiot.

 

[amaferanga]

If you run a new chain on a knackered ring you'll knacker the chain.

Please explain

Surely if a chainring is actually knackered then a new chain won't run on it at all anyway.

 

[Cubist]

If it were mine I'd change the middle and outer rings. The gap between the teeth on the middle ring are quite scooped, especially at about 3 o'clock on the second photo. If you were running an old chain I'd leave it, but it'll not mesh well with a new one. Granny's OK.

 

[Jimmy Doug]

If it were mine I'd change the middle and outer rings. The gap between the teeth on the middle ring are quite scooped, especially at about 3 o'clock on the second photo. If you were running an old chain I'd leave it, but it'll not mesh well with a new one. Granny's OK.

I can't change the rings on this crankset - it's a cheapy one.

 

[mickle]

Please explain

Surely if a chainring is actually knackered then a new chain won't run on it at all anyway.

In an ideal world a chain should fit a sprocket (for that is what a chain ring is) snugly. Not too tight and not loose. In use, as each roller meets it's destination tooth it should stop moving. Roller is a bit of a misnomer, you don't actually want the roller to roll. Any mismatch of tolerance causes the chain to shrug around the sprocket. And movement = wear.

 

[Jimmy Doug]

How does a worn chainring eat into a chain? I can't see how that'd happen. A worn chain will wear out a new chainring, but not the other way round as far as I can tell.

I found these simple pictures that for me show clearly what happens. When I look at them, I can see how a worn chain can wear a sproket; and how a sproket can wear a chain:

 

[gbb]

Thanks for all the feedback. I took the crankset to my lbs yesterday, and he basically confirmed what everyone here has said: it is slightly damaged but it shouldn't be so damaged as to wear out a chain. He did ask me if my chain was too slack - a question I found surprising because I didn't think a slack chain would cause premature chain wear. What do you guys say about this? In any case, I will change the crankset for a slightly better one - just to make sure.

Walk away and don't look back, he's obviously an idiot.

Agreed.

Barring the other points made, a slack chain won't cause any more wear compared with a correct chain. Thats because there are a fixed amount of links between the top of the cassette and the top of the chainrings...the only part of the chain thats under stress. All of he rest of the chain under the transmission is not under stress. However many more links there are doesnt matter because they're not under stress...its the stress on the top during pedalling that causes most wear.

 

[02GF74]

How does a worn chainring eat into a chain? .

With a new chain and new rings, all the chain rollers will rest on the chain ring tooth edges. Imagine the teeth are worn i.e. have beome narrower. This is an oversimplification but the chain will rest on one tooth and there will be gaps between the rollers and the teeth after it due to the narrower teeth so they are not sharing the load, the leading tooth will see be more load = more friction = qucker wear on the chain. The rate of wear will reduce once the chain meshes with the teeth.... by which point your ave ruined a good chain.

Try it as report back.

 

[Jimmy Doug]

Well, if a slack chain can't increase wear, that means it can only be the chainring. It was a brand new chain with a brand new cassette. I usually manage to do around 3000 to 4000 kms on a chain, as I clean and lub them often, yet this chain has only done 500 kms. There can be no other cause for this other than the chainring - even if it isn't totally worn out. I really wonder whether it has something to do with those little shards of metal. They don't come out well in the photo, but they're sharp buggers!

 

[amaferanga]

In the real world though a new chain on a knackered chainring just won't be usable - you'd get so much chain-suck that you wouldn't get far enough to wear out the chain.

 

[Jimmy Doug]

In the real world though a new chain on a knackered chainring just won't be usable - you'd get so much chain-suck that you wouldn't get far enough to wear out the chain.

Wouldn't chain suck only occur when changing from the middle ring to the granny gear? If so, I hardly ever use my granny gear, which accounts for the fact that it is the only ring on my chainring which isn't worn.

 

[Cubist]

Wouldn't chain suck only occur when changing from the middle ring to the granny gear? If so, I hardly ever use my granny gear, which accounts for the fact that it is the only ring on my chainring which isn't worn.

Chain suck stops the chain from leaving the chainring smoothly at the bottom, and in extreme cases sticking to the worn teeth and balling up. It isn't just restricted to shifting issues- I had it on a granny ring (it gets used a lot here in the Pennines off road) and it caused running as well as shifting problems, with the chain pushing and pulling at the rear mech.

 

[Jimmy Doug]

Chain suck stops the chain from leaving the chainring smoothly at the bottom, and in extreme cases sticking to the worn teeth and balling up. It isn't just restricted to shifting issues- I had it on a granny ring (it gets used a lot here in the Pennines off road) and it caused running as well as shifting problems, with the chain pushing and pulling at the rear mech.

Could this be what I was experiencing? As I said in my first post, the transmission would often clunk, sometimes quite loudly, as though it hadn't properly engaged. It almost always happened in a low gear and when I put the chain under tension, eg when I'd just changed down, or going uphill. I wrote a post here

 

[Cubist]

Could this be what I was experiencing? As I said in my first post, the transmission would often clunk, sometimes quite loudly, as though it hadn't properly engaged. It almost always happened in a low gear and when I put the chain under tension, eg when I'd just changed down, or going uphill. I wrote a post here

Yep, I reckon so. It's what happened with mine, that clunk as the chain rode up the back of the ring and the rear mech flipping back as the tension released.
In that thread you mentioned a slightly loose jockey wheel. The top one will always have a little bit of designed-in play or float to ensure it meshes properly, otherwise rear mech adjustment would be constantly critical.