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  1. #1
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    Chain trying to skip at hight torque on largest cog

    I just built hd3 and having this issue. It only happens at really high torques on punchy climbs or techy punches. To me it seems like the chainline is not ideal when shifted to highest cog, but i followed all instruction and installed everything correctly. It would seem like the angle of chain leaving the cog towards the ring is too big. My cassette is 11 speed 10-42 and chainring is 32 race face, with next cranks. i have 2 spacers on drive side and one on non drive side per instructions. I am thinking of getting rid of one drive side spacer to bias the chainline towards the big cogs. There are no other issues, it shifts flawlessly, all parts are new. Any ideas?

  2. #2
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    In my experience, chainline coming off the big cog will not cause a skip because the chain is properly engaging the cog starting at the bottom where it's fed onto it by the upper jockey wheel. Being fed onto the ring at a large angle could possibly cause a problem with the chain engaging the ring, but if it's not coming off the ring I kinda doubt that's causing a skip. I'd check the rear derailleur alignment and adjustment and check that the axle and rear sus pivots are secure.

    Depending on the crank and ring, some differ for boost, typically the ring having less inward offset. Running a standard offset chainring moves the chainline in 3mm which improves things for the largest cogs. You need to check clearance between the ring and chainstay.

    Here's the RaceFace chainline info: https://www.raceface.com/media/Crank...chainlines.pdf

    Finally, is the chain skipping on the cassette or is the freehub slipping.

    Did you torque the cassette to spec? Sometimes there's quite a bit of friction tightening a cassette on an XD driver and it might require more torque than you think. This wouldn't be the source of skipping as the cassette spline engage the freehub for some distance.
    Do the math.

  3. #3
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    thanks, for the lack of terms i used "skip" but it does not skip really, just a weird metal noise, like it wants to come of off top of the ring or it catches on the tooth it is disengaging. really hard to describe it and hard to tell as i can only replicate the situation on the steep punch and i am unable to be looking back at the cassette to see what is going on.

    the race face guide you linked is what i used to set everything up and i am pretty sure i got this right.
    using race face next cranks with race face ring (not flipped).

  4. #4
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    It's possible your limit screw is not set properly, and maybe causing the chain to try to run on top of the 42t or trying to shift to the smaller cog.
    Ideally the upper pulley must be aligned with the 42t cog, but under stress things tend to flex a bit so try to play with it a bit.
    And as mentioned, give a good wrench on the cassette, without a torque wrench people tend to under tight the cassette and over tight everything else on the bike .

    EDIT: check you cassette for damaged and bent teeth.

  5. #5
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    I have new oval ring on order with 6mm offset instead of 3mm. That should give better chainline even though its not meant for boost. And hopefully will fix the issue. I wanted to try oval anyway.

  6. #6
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    just an update on the issue. got 32t Absolute Black oval ring for 49mm chainline (instead of 52mm suggested for my boost HD). this got rid of the issue i was having on 42t ring but not affected shifting or anything else. the chain line looks better just by looking at it. the only downside is the clearance between ring and chain stay is a bit tight at the maximum ovality, but i can live with that.

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