Finally replaced the drivetrain on my 2019 yt jeffsy. I replaced the chain and cassette, but seem to be having an issue with the new chain jumping off of the chainring. The new chain is the same length as the old chain, measured it exactly and used a chain breaker to get it to size. It seems to be jumping a bit as I go from high gears to low gears but as I get to the high gears it will jump off

Is the chainring too worn out? am I better off just replacing it, or is a different issue causing this.

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  • 1
    Could you get a pic of the chainring square-on so we can look at the tooth profiles?
    – MaplePanda
    Commented Aug 15, 2021 at 18:43
  • 1
    Any stiff chain links? Though I guess they would have trouble passing through the rear derailleur.
    – Michael
    Commented Aug 15, 2021 at 19:09

1 Answer 1


Great video - shows that your chain is riding up on the teeth of the single chainring, and then dropping back down into the teeth or off to the inside.

I doubt its the chainring teeth, they look fine other than having paint scraped off.

First, get a marker pen and do the same setup as video. Slowly turn the crank and as soon as it steps up onto the peaks, mark the chain at that point (red sharpie pen works on an inner plate)

Then crank again. I suspect you'll find the same place on the chain falls off repeatedly.

This would suggest its a problem with the chain at that location, a stiff link from joining, or a bent link, or something else like a bit of debris caught inside the chain.

  • 1
    So it only rides up when i shift gears, if i am not shifting gears, then it stays on the chainring without issue
    – Bobbygllh
    Commented Aug 15, 2021 at 19:29
  • 3
    One tooth may be bent sideways, just very slightly. Remove the chain, look from above and turn the crank. Observe the teeth.
    – Carel
    Commented Aug 15, 2021 at 19:50
  • 2
    just kidding, it ended up being the quick link not properly attached. Complete miss on my part to not double check that. thank you for the detailed answer
    – Bobbygllh
    Commented Aug 15, 2021 at 21:54

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