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  1. #1
    what?
    Reputation: Padronis's Avatar
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    Skipping chain is going to drive me up a wall!

    Or maybe it won't because it sill skip as soon as I give it any kind of pressure.

    Anyway, I have an 06 Specialized Rockhopper Comp Disc with a RaceFace Evolve X-type crank. I've had the bike for about 3 months and the crank for about 2. My chain tends to skip off of the middle ring and onto the small ring or all the way off as soon as I start climbing on the trail. It's fine when I am just pedaling on the flatness. I have taken it to the bike shop and they checked the derailleurs, casette, chain, rings... The only thing they could come up with is that I had 1 too many spacers on the drive side. So I took one out and added it to the non drive side. Today I went out and at first it seemed like it helped but then it started...and began to skip just as often as it did before. Anyone have some suggestions before I lose my sanity?!

  2. #2
    Blanco
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    If it skips while climibng, this means it skips when you're in the middle ring and large rear cog, right?

    If so, and the obvious stuff is OK (chainring isn't bent, derailleur isn't rubbing, chain doesn't have any tight links), it sounds like your chainline is too wide at the bottom bracket.

    Different cranksets put the chainrings in different places...maybe the Race Face cranks put the rings too far outboard compared to the stock cranks? That's the first thing I'd look at.

    (I don't have time to write an explanation of how to measure chainline, unfortunately. Maybe someone else can help this guy.)

  3. #3
    what?
    Reputation: Padronis's Avatar
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    Thanks. You have my gearing right. I use the middle ring and either the 3 or 4th cog. I rarely go higher than that. I already removed one spacer from the drive side because they said the driveline was a bit extreme. Maybe I need to move the last spacer...

  4. #4
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    Sounds like the chain line is out.

    I think shimano says the middle chain ring should measure 49.5 to 50mm from the center of the frame. Once that it taken care of, check the swingarm alignment. If you are in the middle ring and are on the middle rear cog the chain should be straight or close to it.

    Phil

  5. #5
    Blanco
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    Oh, duh.

    Measuring the front is easy. Flip the bike over and measure your BB -- it's probably 68mm, but make sure.

    Then measure the distance from the far side of the BB to the middle chainring, and subtract half of 68mm (34mm). That'll give your chainline.

    For a standard 135mm rear, 47.5mm is usually the chainline you want -- although you frequently can't get it that far in due to FD clearance, and usually anything under 50mm will work OK.

    Yours is probably much wider, and you may need a shorter BB spindle to fix it if the spacer doesn't get you enough room.

  6. #6
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    Quote Originally Posted by Phantomtracer
    I think shimano says the middle chain ring should measure 49.5 to 50mm from the center of the frame. Once that it taken care of, check the swingarm alignment. If you are in the middle ring and are on the middle rear cog the chain should be straight or close to it.

    Phil
    I had the same problem with new cassette, rings, and chain, old derailer. Guess what the problem was. After my non-expert examination of the derailer, it felt functionaly fine . As the only old part, I changed it. Drivetrain works great now. I suspect one or more of the springs was worn and while stressed could not hold the chain tight causing it to skip and derail.

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