Unanswered Jam2 6.8+ 2019: Chain jumps occasionally on smallest sprocket

[pegnose]

If I am driving in the highest gear, particularly in acceleration phases, the chain jumps occasionally. Is this normal due to the high torque with motor support, or is it due to new material getting used to each other and will disappear with time?

 

[steve_sordy]

I'm assuming from the wording that the bike is relatively new. If so the chain should not be jumping at all. Therefore there is something wrong with the set up.

First things first, check the the axle is not loose, ie at the correct torque. If it is loose the cassette can move and the shifting is thrown out. Are the limit screws set correctly? If the limit screw is incorrectly adjusted it could be close enough to let the chain engage the small gear, but not enough to let the chain settle properly into place. Is the cable tension slack enough to allow the mech to move the chain over?

 

[pegnose]

Yes, the bike is very new. The chain is not jumping if I step into the pedal very loosely. Just on acceleration phases, e.g. after a red light. I know, I can shift to a lower gear and then everything is fine. But it also happens that, e.g., I want to bypass a front rider, and stand up for more force. Then it happens as well.

I will check in with the bike shop where the bike got deliver to.

Thanks!

 

[pegnose]

So the axle is not loose. The lower limit screw might be a little too far out, though. On my way to the bike shop the chain hopped off completely. Will get checked on, the first service check-up is due anyways.

 

[steve_sordy]

Limit screw adjustment is dead easy! Like really really easy.

 

[MattyB]

Just double check the limit screws and indexing, I suspect your derailleur alignment is just a tad out.

 

[steve_sordy]

Mech hanger alignment can produce symptoms that look like lots of other stuff. Only when all else failed did I even think to check the hanger alignment. Problem is that the hanger is so small that unless the mech is off at a big angle most people never think to check it. You need a proper tool that costs about £25-30 to fix it. Easy to do though, and it doesn't take long.

When I had a 12-speed clockwork bike, the mech was always getting knocked. The tolerances on the 12-speed are very tight and to get smooth faultless shifting the mech alignment needs to be spot on. I never needed to get my hanger aligned until I had a 12-speed system, then it was in he LBS every other month until I bought the alignment tool. Used it once and never had another problem until I used it earlier this week on my 11-speed emtb.

 

[pegnose]

Thanks for the advice, guys! I know it's not hard. And I will be doing it myself in the future. But currently I don't have a proper work space for this and the bike will be at first-time inspection next week anyways.

I'll probably get back to you, if I may, because I don't know half of the terms you are using. I have written scientific theses in English, but I have absolutely no vocabulary for bike parts or mechanical parts and tools, whatsoever. Feeling a little clumsy.

EDIT: Just found a video showing what tool you are talking about for aligning the mech hanger (also a new word for me).

EDIT: What does indexing refer to in this context?

 

[steve_sordy]

"Indexing" means setting up the shifters and mech (derailleur) to change gear properly.

 

[pegnose]

Got my bike back from first-time maintenance today. Turns out they replaced the smallest two sprockets.