Chain rests on chainring teeth when in extreme gears

[confusedcyclist]

HELP!

On the way into work yesterday my chain started dropping repeatedly. On the way home my chain snapped, as I pulled over at the kerb it rolled off the cassette and fell down a storm drain (there's a tale for the kids!)

Luckily I was near a Halfords and was able to coast most of the way downhill for a replacement chain. The return journey home was a bit smoother, but I still noticed issues while in low gear, particularly when the gears were in extremes. (I don't normally ride with gears in extremes for prolonged periods, just if I get caught by surprise at a light etc.)

I noticed when I got home that sometimes with the cassette on largest cog and chain on the outer largest (ring) the chain mounts the tips of the sprockets. The chainring doesn't look particularly worn, no obvious broken teeth or bends, and stifflinks can be ruled out with the new chain. I tried moving the stop limiter on the FD for the outer chainring but still having problems. I found the image below which seems to resemble the issue, but it's not my bike so don't go by what you can see there. The FD hasn't twisted on the seat post either. What am I missing?

This issue has appeared spontaneously, I haven't done any adjustments to the FD etc and the bike is well serviced and lubricated, the gear cable is relatively new as well, this leads me to believe it might be wear on the chainring, I'll post my own images later if required.

Thoughts?

 

[mjr]

Was it a sudden failure or had that chain been on for a long time?

If you ran a chain until it snapped, it seems quite likely that the chainring has worn beyond tolerance too.

 

[confusedcyclist]

Unlikely, the prior chain was only 5 months old and wasn't worn at all at the last check <1 month ago. I've ordered a new chainring to see if that sorts it though, worst case scenario, I have a spare chainring for when it's needed.

 

[Onyer]

When I bought my Cervelo in September I had the same issue with a Rotor chainring. Except that the chain would sit on the smallest chainring when changing down. I took it back to the shop and their solution was to change it to a Shimano. It's been as smooth as silk since without an issue. I would hazard a guess that like me you have a rogue chainset. Changing the chainring will hopefully solve the problem for you.

 

[youngoldbloke]

Did you shorten the new chain to the same length as the original? BTW the condition is known as chain 'skating'. (I was involved in a long thread about the problem some years ago on 'Bike Forums', but in my case the trouble arose when dropping down to the inner ring, so not quite the same. I solved it eventually by flipping over the inner chain ring which affected the spacing of the chain rings. NB - this was a Campag Veloce 10 speed setup)

 

[confusedcyclist]

Did you shorten the new chain to the same length as the original?

I didn't have the chain to compare as it went down a drain, so I can only hope so. I think this issue of sitting on the teeth was there before it snapped anyway.

 

[youngoldbloke]

see my edit

 

[berty bassett]

i know this is not going to help in the slightest but it doesn't look like the ring is worn to me ! are you sure its the right chain or the right chainring - does it happen a little bit on the inner ring ? - i am really interested to find out why this is happening - told you i was no help - wish you luck - will keep an eye on this to see what the mechanical people think and hopefully learn something

 

[confusedcyclist]

@berty bassett, the photo isn't of my chainring. It's just showing the skating that I have been experiencing. My chainring is however considerably worn compared to the above image (but not quite sharks teeth). It's quite likely that wear is the problem. It's done about 6k miles in our northern (wet & grimy!) weather conditions.

 

[confusedcyclist]

see my edit

Interesting, your post implies your problem started after a change of chainring, am I right? My chain ring was the stock shimano F565 compact crank fitting so I don't think flipping it is a solution? It's been on 6,000 miles without issue, so probably just worn out.

 

[Ajax Bay]

Think we deserve a photo of your chainring @confusedcyclist (acknowledging that you said quite clearly in OP the image wasn't your one) with the new chain on it. If you do allow 'extremes' eg large to large occasionally, and since after being caught at lights you'll be stomping off on the amber (ie peakish power), those episodes over 6k miles may well have shot your large chainwheel and the new chain has complained/revealed that it's time for a new chainwheel. So I'd put the 'spare' chainwheel on pending arrival of the one you've ordered.

 

[confusedcyclist]

Ok, I went down to the garage especially for you so don't say I never did anything for you @Ajax Bay

From drive side after a few rotations while in large and large.

Close up from other side. Yes now I am reflecting on the image, very worn.

 

[Andy_R]

Yeah..your bike is seriously fecked on the chainstay and seatstay. Your saddle is too high making the perineum/ablaster/glute angle all wrong and you will only be able to ride a bike again with years of research and trial. Give me the bike for medical research and I'll see what I can do for you (I hold out no hope to return your bike to you as it may be needed to strip down to component level)

And if you need to move any UK currency to help in this matter, I have a Nigerian uncle who works in the Embassy

 

[confusedcyclist]

I'm paying you to take it away? Do you accept bitcoin?

 

[Andy_R]

teeth are worn worse than Shane McGowan before he got his new bridge...new chainrings sir!