Crankycrank

I'm not really trying to criticize you here just noting that the shop can possibly use that argument in a dispute. If the chain was just popping that would seem even more evidence that it was the chain coming apart since if the cassette hub or jockey wheels were sticking you would probably feel a slight skip or tug. Worn cassette teeth would also skip. I always just try to encourage people to learn to do their own repairs as it can save a few headaches, time and $$$. No judgement from here if you don't though.

woodcraft

Partial quote cyccommute

"Chainsuck has nothing to do with a cassette. The chain is under tension as it goes over the top of the cassette and can't be "sucked" downward since the chainring is pulling on the chain.



It's not mysterious and is almost predictable. Chainsuck is where the chain sucks up into the frame as the chain leaves the bottom of the chainwheels. The chain holds onto the chainring too long and it gets pulled up. The rear derailer usually has enough tension to pull the chain off the chainwheel but if the chainwheel is damaged, the chain can stick onto the wheel. Even small burrs that develop from a shifting error or poorly adjusted front derailer...like when you hear a "grindy" or "clattery" shift.

I would also disagree that the chain can jam between the lower jockey wheel and the rear derailer cage. There's just not enough room for the chain to jump off the pulley and jam. It would rerail rather than jam.

I do agree that lots of stuff can happen that might not be the mechanics fault.


I can't absolve the mechanic entirely but there are other possible causes that have nothing to do with the mechanic. You said you were in the smallest chainring and went to make a shift. The smallest chainring is the one most likely to have chainsuck problems. The chain is under less tension from the rear derailer spring because the chain is effectively "longer" and more slack in the inner ring. The derailer arm is also flatter so it puts less tension on the chain. If the chain catches on the ring and starts to "suck" upward and suddenly releases, the energy goes into the rear derailer which swings that flatter arm upward and allows it to contact the cassette or catch the chain. That pulls the spring on the hanger upwards and the next thing you know the system jams and goes for a wrong way trip around the cassette."




Thanks for the chainsuck details. I should have said new chain/old chainrings.

Not seeing or able to create on the stand how the RD can swing into the cassette.

I give 50/50 on straightening the hanger. If it goes back into position will likely work OK, but less likely to survive a second bending.

cyccommute 

The disc did nothing to protect the spokes in this case. The dork disc only protects against the chain going behind the cassette on over shifts when the derailer is improperly adjusted. You may have dented the plastic but it offered no protection because your chain was no where near the spokes.


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3000 miles is a lot of mileage. The burrs that form are a random event that can occur in the first 10th of a mile or the last 10th of a mile or anywhere in between. They probably form often but are somewhat self-correcting as the chain pulls off most of them. But, occasionally, they don't.

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No, I wouldn't say the onus is on the mechanic to inspect the cassette and chainrings. You didn't ask them to inspect the chainrings, only to change the chain. They aren't psychic nor clairvoyant. And a burr can be incredibly small. Often, you can only find it by looking closely at each tooth and testing to see if it will hook your fingernail.

Your hanger is twisted way back from where it was originally, which is almost directly under the axle. The twist to the hanger is bad enough but it's also displaced about the width (or more) of the hanger rearward. That means that the dropout has been bent backwards too. Steel is tough but there are limits. I would say that you've passed those limits.

fastk9dad

Not sure if it is a result of the chain-suck and resulting damage but the rear wheel isn't completely seated in the drop out. In the photos you can clearly see where the nut is normally seated, a few mm higher than where it rests now,

Pavol Stromcek

No offense, but I strongly disagree with you on this. The mechanic isn't blind - there's no need for clairvoyance, for christ's sake! A good mechanic can easily look over the cassette and chainrings and assess how worn they are. Besides, it is common knowledge that replacing a chain will often also involve replacing the cassette (and it wouldn't seem far-fetched to also look at the chainrings). The mechanic I dealt with in this scenario did indeed take a quick look at the cassette - no clairvoyance was required! A mechanic who doesn't even bring up the cassette during a conversation about replacing a chain would be a bad mechanic, I think.

Troul 

A test ride or even an applied load on the stand to ensure things are operating properly before handing off the saddle to the customer would, imo, point to whom is most liable.


Should a customer that is getting there automobile's oil changed check over the vehicle's oil level & also verify for adequate filter installation before leaving the shop's garage?
No. That is what you are paying them to do.
If the vehicle is leaking something & the technician turns there cheek to what they saw, whether it is oil, brake fluid, gasoline, etc etc, it is on the shop to make the customer aware of the situation.

ramzilla

Looks like the chain got jammed up in the jockey wheels and, when you continued to pedal the whole derailleur got dragged around to the top of the cogs. Quite a mess. I had an issue once with the jockey wheels on my road bike drivetrain. My bike or my chain somehow picked up a small piece of insulated wire off the road. I noticed a repetitive noise coming from the drivetrain. It was embedded in the rear derailleur. Had to use a pair of pliers to pull it out. Weird stuff happens.

70sSanO

robertorolfo

Impossible to know for sure, but if this happened three blocks away from the shop, it's overwhelmingly likely that it's related to the work done at the shop. Things happen, but that's too much of a coincidence. People make mistakes, so there is no need to go ballistic on the mechanic, but it's looking like it's on him.


Normally yes, that's it's job, but you make it sound like it's impossible that anything else could possibly find it's way into the spokes, and that the disc could ever stop that from happening.

cyccommute 

There is no easy way to visually inspect a cassette or chainwheel and reliably tell if they worn. There is a tool that checks the cassette but it isn't widely used. I can't speak to it's reliability either since it isn't something that is widely used. The difference between a serviceable cassette and a worn cassette is so small that a visual inspection of the cassette will not tell you if the cassette is too worn to mate with a new chain. If you haven't allowed your chain to wear too much, the easiest way to tell if it will work is to put it on the bike and go for a ride...carefully. But that will only get you through about 3 chains...which isn't a hard number by any stretch.

The chainwheels are even more difficult to tell if they are worn past the point of being useable. A chainring with serious shark fin teeth on it may still have a lot of life left in it. As for checking for burrs, again, that requires a lot more time and effort to check.

Finally, there is your part in this. I missed the earlier post that Crankycrank responded to above. If the bike is making a noise it didn't make before after some mechanical work has been done on it, it's up to the user to stop using it and take it back to the mechanic so that they can check it. Again, the mechanic isn't clairvoyant. Perhaps the mechanic made a mistake but you are as much as fault as he is for continuing to ride when you noticed a problem.

TiHabanero

Give me 20 minutes with that frame an I will have the hanger and axle slot fixed. It is very unlikely the dropout will crack or break off from bending it back. I have done it dozens of times over the years.

Pavol Stromcek

But even if the hanger and axle slot can be successfully straightened, surely the strength of that part will be compromised?

Dan Burkhart 

My money is on an improperly installed pin.

Pavol Stromcek

Yeah, I do think that is the most plausible explanation due to the busted link, but also given what happened and the timing of the incident (within a minute of my first ride with the new chain). As a proponent of Occam's razor, that's the simplest explanation. If it can be determined that the busted link in the photo is the one with the joining pin, then I'd say it's a pretty clear-cut case of error on the mechanic's part.

At any rate, I'm hoping to hear back from the shop in a day or two, and I'm really anxious to hear what they say.

Glennfordx4

Anytime we install a new chain we test the bike in the stand and make sure it shifts right, we make adjustments if needed then we always test ride the bike and make sure there is no skipping in every gear combo. I really think ( 99% ) the mechanic is at fault here, he missed something whether he had the pin not all the way installed or didn't check his work when the bike was finished. I hope they take care of it for you as this should have not happened from just a chain replacement.

Glenn

Dan Burkhart 

Easy enough to determine. Look at all the other pins and you see a dimple in the centre. The joining pin will be flat on the end an a slightly darker colour.
This is assuming they used a proper joining pin and did not join the chain by pressing the original pin back in. If they did that, the failure was inevitable.

TiHabanero

Significantly weaken the hanger? Not noticeably. Bend it a couple of more times and it will make a difference.

Pavol Stromcek

Good news! I just got a call from the bike shop and they said the bike is "fixed," and that it was totally their fault so, obviously, no charge. The guy said, "You can't even tell that anything happened to it." I was in the middle of putting my 14-month-old son to bed when they called, so I really didn't get a chance to discuss the details of the repair work, but I plan on going over everything in person when I pick it up. But I'm totally relieved that they took full responsibility for it. I'm curious to see if it truly looks as if "nothing happened."

70sSanO

Kontact 

I wouldn't worry about the hanger. If it didn't break bending it back, it's still more than strong enough.

I'd bet it was the pin as well.

CliffordK

Glad to hear the bike is back in one piece. Let us know the final diagnosis.

One thing, if the derailleur or chain never hit the spokes, then all the damage was done by your pedaling.

If something doesn't feel right, then STOP

Pavol Stromcek

So, I got the bike back today. Unfortunately, the mechanic who installed the chain, and who I believe repaired all the damage (I recognized his voice when he called to tell me the repair work was done), was not there, and the guy who was there couldn't tell me much about it beyond simply what was repaired/replaced.

Obviously, they replaced the chain and the rear derailleur, and they straightened the hanger. Haven't had a chance to ride it yet (super busy afternoon), but you can bet I'll stop at the first, faintest sound, or anything that feels amiss, when I do ride it this weekend.

However, some flecks of paint are missing from the part of the hanger that bent, as well as a few other spots on the chain stay. I don't take this bike out in the rain, ever, but if the roads are wet, this is an area of the bike that's going to get pretty damp and grimy, and since this is steel, I'm worried about rust. I'm thinking about going over these spots with primer and seeing if it's possible to get some touch-up paint. Has anyone done this kind of touching up of a frame before? Should I pester the bike shop about this (they are a Bianchi dealer, after all)?

Aubergine 

Cyclist0108

I bought nail polish for my Bianchi. The best part is one of my students "caught" me doing this. Fortunately, where I work, this buys you credibility.

It didn't work too well for the scratches.

cpach

The probability of the rust being a structural problem is very low. Apparently Bianchi actually distributes celeste touchup paint: https://www.bianchi.com/global/store...tCode=C8810001. I think it'd be reasonable to ask them to get some to touch up your bike. Ride it in the meantime.