Chain skipping under load after bike service

2200km and the chain is skipping?
Not surprising, Sounds like a worn out drive train to me.

It also sounds like you don't have a very good bike shop. They should easily pick this up and suggest replacement.
 
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RustyIron said:
Your first mistake was taking it to a the bike store boys. You have the tools. You know what to do.

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I appreciate the suggestion, but is not that simple.

I could have done the gear tuning at home, but not sort out the original problems. I did not want to disassemble the motor to clean it. A lot of people had problems after doing that. Now, I could have tuned it by myself but I wanted them to do the job just in case more complex issues raise.

Plus, not everyone has a large home with a large garage where to arrange a nice benchroom like the typical US houses. I moved here recently and temporarily. I am renting and my garage is filled with boxes ready for the next removal.
 
RustyMTB said:
I kind of agree but you haven't experienced a failure, your drivetrain has shifted from working fine to working but with problems. It's what drivetrains do, there are endless threads on the subject in here. What you could do is spend time learning how they work, how to adjust them for best performance, their weaknesses & failure points. That way you wouldn't need a shop nor a thread every time something happens to your bike. Youtube is a digital Narnia for this stuff, there are endless tutorials on how to look after bikes, why not watch a few of them instead of coming here for advice & then questioning it?!
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Another guy in my ignore list. Bye.
 
pagheca said:
I appreciate the suggestion, but is not that simple.

I could have done the gear tuning at home, but not sort out the original problems. I did not want to disassemble the motor to clean it. A lot of people had problems after doing that. Now, I could have tuned it by myself but I wanted them to do the job just in case more complex issues raise.

Plus, not everyone has a large home with a large garage where to arrange a nice benchroom like the typical US houses. I moved here recently and temporarily. I am renting and my garage is filled with boxes ready for the next removal.
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We get that, but there's going to come times where you can't get to an LBS, like when you're on a trip or adventure and the bike starts playing up in a morning when you've got to ride. You really want to learn and gain the experience of getting things better for yourself for these scenarios as it can destroy a great trip and could be something fairly simple. To do the gears you need a stand of some description, which can be as simple as a piece of wood holding the bike seat up so the wheel is off the floor, and a 3mm allen key. That's it really. But there's little nuances that can kill a weekends riding but be fixed in less than 30s of effort.
We're not all saying you need to be a WC level mechanic, but some knowledge is really important in MTBing.
Think about being 1000' up and you stack your bike on a trail and knock the mech out of alignment, you don't have a mech hanger tool, but armed with some knowledge you'll at least get back home.
 
Yeah, I know that. But again: disassembling and cleaning a motor is not the kind of thing you do while "being 1000' up". And I want the shop to fix the problems they created.
 
If ever a thread epitomised the aphorism don't let perfect be the enemy of good. This guy wants his cake & eat it, asks for advice but won't accept it when offered & insists anything that goes wrong with his bike is someone else's problem before throwing his toys out of the pram repeatedly. What a crock.
 
pagheca said:
maybe. You too. 🤷‍♀️
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My point was, your motor wasn't part of the issue of 'skipping'. Unless i'm very confused.

One other point, your rear wheel cannot be misaligned, you've got a thru-axle into a UDH, therefore there cannot possibly ever in any world be a misalignement there. There can of course be a wheel being untrue, or something else causing the issue, but not a misaligned wheel in the old context of a QR axle/dropouts.

But you can't just focus on "i wouldn't fix a motor 1000m up" as that's just crazy talk, that's like saying you wouldn't replace your brake pads, or wouldn't fix a puncture... It's 1 aspect of a working bike. The motor isn't the issue here in this debate, whatever issue that was you were getting 'serviced' isn't part of the problems you're having. Therefore the debate about fixing and knowing about the other things is equally as valid as it ever way, maybe even more so.

MTBs and gears etc are not rocket science, they're something you learn as you need to, without this knowledge, you're on a waiting list at an LBS and in the hands of good/bad mechanics and 16 year olds who don't know what they'e doing.. it's a lesson many of us have learned in the last 10, 20, 30 years and means a lot of us never need to go to an LBS... we're not trying to be superior here or belittle you, we're trying to help.
 
Weeksy said:
My point was, your motor wasn't part of the issue of 'skipping'. Unless i'm very confused.

One other point, your rear wheel cannot be misaligned, you've got a thru-axle into a UDH, therefore there cannot possibly ever in any world be a misalignement there. There can of course be a wheel being untrue, or something else causing the issue, but not a misaligned wheel in the old context of a QR axle/dropouts.

But you can't just focus on "i wouldn't fix a motor 1000m up" as that's just crazy talk, that's like saying you wouldn't replace your brake pads, or wouldn't fix a puncture... It's 1 aspect of a working bike. The motor isn't the issue here in this debate, whatever issue that was you were getting 'serviced' isn't part of the problems you're having. Therefore the debate about fixing and knowing about the other things is equally as valid as it ever way, maybe even more so.

MTBs and gears etc are not rocket science, they're something you learn as you need to, without this knowledge, you're on a waiting list at an LBS and in the hands of good/bad mechanics and 16 year olds who don't know what they'e doing.. it's a lesson many of us have learned in the last 10, 20, 30 years and means a lot of us never need to go to an LBS... we're not trying to be superior here or belittle you, we're trying to help.
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Sorry, but I'd like to put an end to this pointless back-and-forth.

I actually agree with what you're saying: if you own a bike, you should know how to maintain it. But what I'd like people to understand is that not everyone's situation is the same.

I use my bike pretty much every day: for commuting, having fun, training, and everything else. And please don't tell me I should own eight different bikes for all those purposes, because first, I don't want to, and second, I simply don't have the space. I am not telling others what to do either. Other people, other priorities. And other choices.

As for maintenance, you will probably not trust me, but I know perfectly well how to change a tire (I've done it several times), replace brake pads (done that too), bleed the brakes (the only reason I haven't done that myself is because I didn't want to risk making a complete mess in my garage) etc.

One piece of advice, for everyone: please remember that people don't necessarily tell you every detail of their lives. Not everyone's home, family situation, finances (fortunately that's not my case, but it may well be for others), work commitments, or circumstances are the same.

This constant tendency by some forum members to lecture everyone else makes the atmosphere here far less constructive. I'm not the only one who's noticed it. How about trying to make this a more understanding and empathetic place? After all... come on... we're talking about bicycles, not how to survive a war or cure cancer.

A slightly more relaxed, helpful attitude from everyone would go a long way. Yes, I already know the reply: "Well, you're the one who..." Fair enough, maybe that's true, and if so, I apologize.

But let's all try not to turn every request for technical advice into a territorial pissing contest.

Thanks, and apologies for the rant. I'll leave it there unless anyone has something useful to add about the actual technical issue.
 
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what's so funny about that, @Weeksy?

It looks like some people here is still at the primary school. Really. And this forum is becoming a very unpleasant place to be. A pity.
 
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pagheca said:
what is so funny about that, @Weeksy?

It looks like some people here is still at the primary school. Really. This forum is becoming a very unpleasant place to be. A pity.
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mate, i offered you a LOT of ideas, thoughts and suggestions as did everyone else. You asked what it could be but did nothing with the information anyone provided.
Look at the little cable end for example, if someone has serviced that drivetrain, that involves a new gear cable and a new end-cap, but that's not been done. Looking at your high and low screws i suspect they're both wrong too and you've been told about the B screw by multiple people.
You can google and check the B screw by putting the bike in the largest cog and checking what the gap it, either by eye or the little plastic tool... but you're not going to do that, you're going to take it to the same shit shop that did a shit job.
 
Guess how far back through the thread you have to scroll before finding the last time this guy was advised on how to adjust his B tension? Bonus points for who did that. That's right, DIS GUY!
 
Picked up the bike from the shop today. Everything's sorted. A few of the derailleur adjustment screws had been set incorrectly, but they fixed everything and apologized.

I tested the bike on a steep climb, including under the highest torque I can put through it with the motor in Turbo mode, and not a single chain skip.

Thanks to everyone for the advice, it really helped me ask the right questions at the shop and learn a lot.
 
teK-- said:
Agree. How the hell does this shoddy workmanship leave a bike shop after a "service"
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I agree with you, that shops should thoroughly check the function of a bike before returning it to a customer. Having said that, the reality is that there are a lot of sub-par mechanics out there. I've worked in a lot of shops which hired inexperienced young mechanics "groms" who I certainly wouldn't have let work on my own bike, but the owner either needed someone desperately, with few other options, or else they were cheapskates who didn't want to pay the rate that a proper mechanic would require.

I've experienced it myself from the customer side, for example I was on holiday and had rented a Specialized Turbo Levo for 1-week from a local shop. A few days into the trip, the motor started slipping under any sort of high torque riding, either on steep hills, or even relatively flat accelerations when in turbo mode. Luckily it was toward the end of a very long ride with a lot of elevation gain, and I was able to soft pedal it back on mostly flats and downhills. I brought it back to the shop and the first guy I talked to was clearly a young, inexperienced, mechanic. I described the problem, he took the bike out on a parking lot test ride, and brought it back telling me it worked fine! If I didn't have a lot of experience working in shops myself, and was just a random casual cyclist vacationer, I'm not sure what I would have done, but I very nicely asked to speak to the older senior mechanic who had originally rented me the bike, and asked him to take it out again, and be sure to do a few hard accelerations while in turbo mode. Sure enough, he was back in about 30sec, confirming that the teeth on the belts had likely stripped out. Basically, the new employee had only soft pedaled it in eco or trail mode on flat terrain, and had never subjected it to the loads that triggered the symptom. Even more strangely, he explained to me that they had seen a lot of these type of failures on the Turbo Levo, which suggested to me that it should have been obvious to them based on my initial description that my bike was yet another case of a common problem, rather than some mysterious issue that required me to really push in order to get it diagnosed properly.

I bring all that up, because the OP is describing an issue where his bike skips under power. That can have several causes, which have been addressed pretty thoroughly by previous posters, but my point is that if the shop that did the work didn't test it under the power or torque level that triggers the problem, then they would have no idea they were returning the bike to him with a critical flaw.
 
pagheca said:
Picked up the bike from the shop today. Everything's sorted. A few of the derailleur adjustment screws had been set incorrectly, but they fixed everything and apologized.

I tested the bike on a steep climb, including under the highest torque I can put through it with the motor in Turbo mode, and not a single chain skip.

Thanks to everyone for the advice, it really helped me ask the right questions at the shop and learn a lot.
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Glad to hear they sorted it out for you properly, and you are back on the trail!:)(y)
 
TheKaiser said:
Glad to hear they sorted it out for you properly, and you are back on the trail!:)(y)
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thanks!

Actually is one of the two Trek authorized maintenance centers in the area, and have a good reputation here. A mistake is acceptable, as they also apologized. On my side I made the mistake not to carefully test drive my e-MTB before leaving the shop, that is this: Ferretti Bike Shop: vendita bici, e-bike, mtb e accessori per ciclismo maybe not the best in the world, but not exactly the kind of shabby repair shop one may expect.

And by the way, no need to change the cassette and the chain yet. As I guessed, the problem was caused by an incorrect setting after the service. However, I will soon do it anyway.
 
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cozzy said:
B screw has been turned in too far. You don't have enough chain wrap.
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This is the past (about 90 deg wrap) and current (140 deg wrap) setting. The difference is striking. I took some pictures to remember which is the right position.

Thanks again for the advice, folks.

1783063901481.webp
1783063809770.webp


p.s. The friction is still off because I took out the wheel to put it in the car yesterday but it works fine also in this position.
 
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pagheca said:
This is the past (about 90 deg wrap) and current (140 deg wrap) setting. The difference is striking. I took some pictures to remember which is the right position.

Thanks again for the advice.

View attachment 187965 View attachment 187964

p.s. The friction is still off because I took out the wheel to put it in the car yesterday but it works fine also in this position.
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I'm sure it does work fine in that position, that is not its function. It is a friction clutch to stop the chain whipping up and down and causing the lower mech arm to move back and forth. By restricting the back and forth movement, the chain whip is reduced.
 
RustyIron said:
Being the tolerant and forgiving sort of bloke I am, a couple days ago I deleted my Ignore List. Maybe I'll regret the hasty decision, but I can always start a new one.
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So am I but timewasters on missions to teach the world of their sins are to be avoided.
 
pagheca said:
Thanks to everyone for the advice, it really helped me ask the right questions at the shop and learn a lot.
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Good to hear you got it sorted.

Great diagnosis from the members here too.

Not great that you had to point out to a 'professional' shop what the issue might be... that they caused.

58 posts and probably 300yrs+ of real world bicycle experience commented vs an inexperienced mechanic that probably spent 1 year doing bike sales then promoted to bike mech. Surely that would encourage a bloke to learn the simple skills to service/tune the bike and swap out consumable components. Never mind the wasted time of having to take a bike to a shop and having it sit there for a few days.
 
ozzybmx said:
Good to hear you got it sorted.

Great diagnosis from the members here too.

Not great that you had to point out to a 'professional' shop what the issue might be... that they caused.

58 posts and probably 300yrs+ of real world bicycle experience commented vs an inexperienced mechanic that probably spent 1 year doing bike sales then promoted to bike mech. Surely that would encourage a bloke to learn the simple skills to service/tune the bike and swap out consumable components. Never mind the wasted time of having to take a bike to a shop and having it sit there for a few days.
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Thanks for your message. However, personally, I wouldn't be so harsh over a mistake. As I said, that workshop has an excellent reputation in a city like Bologna, where cycling is extremely widespread.

Also, some (not all) of the advice given in this thread turned out to be incorrect. And it was delivered quite aggressively, which, frankly, is something I'd rather not like on a forum and made this discussion very unpleasant.
 
Your cassette is worn af…. The bike shop probably put a new chain on … there lies the problem…. New chain with worn-out cassette = chain slipping under load …. Will happen every time, every bike … and the cassette is worn!
 
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