Torqued my crank bolt, now this is happening . . .- Mtbr.com
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  1. #1
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    Torqued my crank bolt, now this is happening . . .

    I pulled my crankset (Specialized Strongarm II, square taper) in order to service one of the pivot bearings thatís hiding behind there. Finished up, reinstalled the crankset, and tightened it to 30 ft/lbs using a torque wrench.


    All seemed fine, except now when in the middle chainring and smallest cog, the chain will occasionally catch one of the big ringís lifter pins, causing it to skip/pop. Apparently the crankset is slightly farther down on the spindle than it previously was; just enough for it to occasionally get caught by the pin.


    Itís only in this gear combo that it does this. I know the easy option is to simply avoid shifting into this particular gear, but is there something I can do to fix this?
    Attached Thumbnails Attached Thumbnails Torqued my crank bolt, now this is happening . . .-kimg0080-1-.jpg  


  2. #2
    Always in the wrong gear
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    Quote Originally Posted by chakotay View Post
    Apparently the crankset is slightly farther down on the spindle than it previously was; just enough for it to occasionally get caught by the pin.
    My first thought was this too. If that's the case, there's not much you can do. I suppose you might be able to shim it with some very thin metal. Not sure how advisable that is for the health of the crank arm but as proof of concept you could slip a piece of aluminum can in there on at least 2 of the BB spindle faces and tighten it down. If it stops the chain grab, at least you know what went wrong.

  3. #3
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    Not sure if i understand the problem. When you say the crankarm sits further on the spindle...do you mean its the wrong axle length, changing the chainline. If so, you sure its the correct BB shell width and axle length for your bike? Could try to put a spacer on the drive side BB.

  4. #4
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    Tweak the FD adjustment?

  5. #5
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    That happened to me before. I accidentally put my square taper spindle the other way around when I installed it back, the drive side went further inwards messing up the chainline.

  6. #6
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    Quote Originally Posted by joeadnan View Post
    Tweak the FD adjustment?
    Exactly what I was thinking.

  7. #7
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    Is the big ring slightly bent inwards? I've seen that before and definitely makes the ramp pins catch.

  8. #8
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    That's called cross chaining, don't do it, simple as that.

    Quote Originally Posted by chakotay View Post
    .........All seemed fine, except now when in the middle chainring and smallest cog, the chain will occasionally catch one of the big ringís lifter pins, causing it to skip/pop. Apparently the crankset is slightly farther down on the spindle than it previously was; just enough for it to occasionally get caught by the pin.

    Itís only in this gear combo that it does this. I know the easy option is to simply avoid shifting into this particular gear, but is there something I can do to fix this?
    Quote Originally Posted by Harold
    You're doing mtbr wrong, you're supposed to get increasingly offended by the implications that you're doing ANYTHING wrong.

  9. #9
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    That's not a cross over gear... Did you remove the bb spindle? Does it do this while riding or only in the work stand? Do you even use this gear combo when out on a trail?

  10. #10
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    The middle ring/small cog combo should be totally usable. Unless you greased the spindle before you installed the crankarm I don't believe it's possible that you compressed the crankarm too far down the spindle torquing it @ 30 ft. lbs. I'm not sure how the position changed that much from before but a 1mm spacer on the drive side should do the trick, adjusting the front derailleur won't

  11. #11
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    I'm with JB on this one. Nothing should have changed.

    If you've removed the BB, then I'd make sure your spindle is installed correctly, then fix this with neccessary spacers.

    I wouldn't adjust the front derailleur unless its rubbing the chain already, or otherwise needs adjustment.

  12. #12
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    Just for clarification, all I did was pull the crank and reinstall it. I didn't touch the bottom bracket (except to clean the spindle of any grease). The middle ring/small cog combo didn't do this before; so something has changed. Yes, it does it on the stand and during actual riding. The only thing I can think of is that the crank simply wasn't torqued down as much before as it is now. How many times can you pull a crank and put it back on before something stretches out? I guess I could loosen it by pulling it back out a tad; but then it wouldn't be torqued to spec. A shim was the second thing I thought of, but where exactly would it go? (filing the lifter pin was the first thing).

    I supposed the prudent thing to do is pull the crankset back off and reinstall it again and see if it still does it.

  13. #13
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    I have taken them off dozens of times without issue. If it was loose then the square hole in the arm could be sloppy. When that happens you need a new crank. You would probably notice the slop though. It should have been fairly difficult to remove with the crank arm puller.

  14. #14
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    You don't want to loosen the crankarm bolt, that interface relies on a tight connection to maintain integrity. If it was not properly torqued before and ridden loose the square flats on the crankarms (soft aluminum) will deform, sometime drastically and then when you re-torque the crankarm down it will definitely sink farther down the spindle. Once that happens the crankarm will require constant re-torquing and eventually fail completely.

    If done correctly the cranks can be removed & serviced numerous times without problems, but if done incorrectly once is about it.

    It sounds like more than likely they went back on just a fraction more than they were before and are just nicking those rivets. A slight amount of filing may work fine, a 1mm spacer would fit between the drive side cup and the bottom bracket.

  15. #15
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    Quote Originally Posted by dledinger View Post
    I have taken them off dozens of times without issue. If it was loose then the square hole in the arm could be sloppy. When that happens you need a new crank. You would probably notice the slop though. It should have been fairly difficult to remove with the crank arm puller.
    ^That too

  16. #16
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    Pulling the crankset and reinstalling it could make matters worse if you retighten the crankset further onto the spindle. But, Check for wobble in the chainrings before you remove the crank, and make sure to mark the bb spindle and crank to know which square went to which taper. sometimes just changing the attitude of the crankset on the taper will change the wobble and allow the chain to not hang up in the middle/smallcog.
    You might also try to adjust the front deraileur to rub just a bit on the chain when in the middle/smallcog to prevent the chain from catching on the shift pin.
    As for shims, in the "old days" i had cut tiny shims from a beer can to line the square hole of the crankset and keep using a square taper crank that had been overtightened. I had worse chainring wobble problems after that as the shim material was hard to keep in place to allow the crank to set perfectly onto the taper of the BB spindle.
    good luck

  17. #17
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    Shim the bottom bracket at the BB shell, not the crank/BB interface.

  18. #18
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    Quote Originally Posted by chakotay View Post
    How many times can you pull a crank and put it back on before something stretches out?
    This was one of the disadvantages of square taper. You can remove/reinstall it a number of times, but eventually, the interface between the crank/bb will allow the crank arms to settle deeper onto the BB spindle.

    IIRC, the Strongarm II was the OEM crankset on my 2003 Stumpy FSR, except it used the Shimano Octalink interface. How old are yours? How old is your BB? It could be either the crankset or the BB, or it could be both of them. I'd run through checking to make sure the chainrings are plenty tight and anything else that might affect chainline. You didn't mention if the FD cage was rubbing on the chain, helping to push it onto the bigger chainring. I'm guessing not, but I want to be certain.

  19. #19
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    It's a 2003 Rockhopper FSR. The cranks and BB are original. Where exactly would the shim go? I've heard on the spindle (I get this) and on the BB shell (someone will have to explain that.)

  20. #20
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    I would not try shimming the spindle. IMO, that would be very likely to exaccerbate your problems. I've tried it with beer cans too, but on cranks that were worn out and had a very screwed up interface. Even then it was a very temporary fix that never lasted long.

  21. #21
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    Quote Originally Posted by Harold View Post
    You didn't mention if the FD cage was rubbing on the chain, helping to push it onto the bigger chainring.
    I thought briefly about this when reading the initial post....but If everything went together the same, any rubbing in the smallest cog should be on the wrong side of the chain.

    If not, there would be pretty signifigant rubbing in the bigger cogs.

  22. #22
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    Quote Originally Posted by chakotay View Post
    It's a 2003 Rockhopper FSR. The cranks and BB are original. Where exactly would the shim go? I've heard on the spindle (I get this) and on the BB shell (someone will have to explain that.)
    I'm gonna go out on a limb and say it's time for new ones.

  23. #23
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    ugh! It was working just fine . . . then I decided to "fix" it. :P

    Do you think I could get away with just buying a new bottom bracket (the cheapest option)?

  24. #24
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    If the crankarm is torqued too far down the spindle the problem is with the crank, not the bottom bracket. Just try a spacer. You need to remove the bb and install it between the drive side bb cup and the frame.

    Or don't use that gear.

  25. #25
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    The bottom bracket shaft is hardened steel...the crank is not. If anything is deformed or worn it is the crank arm.

    If the bottom bracket bearings are good you stand to gain nothing by repacing it.

    I agree that its old. But its more a matter of wear and tear on the bearings than age. your chainrings look to be in good shape, so I suspect the BB is just fine.

  26. #26
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    yeah, I've already considered adjusting my RD's limit to exclude that gear, but it will just bug me that it's not fixed. Is there a thread that shows how to add a spacer to the bb? I've never actually removed one before.

  27. #27
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    You don't want to limit your rear derailleur - at least I wouldn't - because you'll still use that gear when in the biggest chainring.

    If that's the route you want to go just don't use the smallest cog when in the middle chainring. The gear is redundant and not needed anyway.

    I know you want this fixed "right", but you have to decide if its worth the headache/time/money.

    The spacer would go between the drive side bottom bracket lip and the shell of the frame. You'll need the splined tool to remove the bottom bracket. You can google "bottom bracket spacer" and see a lot of pictures of how this works.

    On triples and doubles I always figure that not all gear combos are good. For example, there's no need to go big-big, or small-small. There's a lot of redundancy in this setup.

    Personally, I would chalk this problem up to that doctrine and leave it be.

  28. #28
    > /dev/null 2&>1
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    What if you spaced the big ring a little bit outboard with veeeeery slim washers at the chainring bolts? From an FD indexing perspective, it should still work because when you upshift to big ring, the shifter allows you to push a little past the indexing point, until the chain gets up on the big ring, after which you let it rest back down on the indexing point.

    I've never done this, but, it might be worth a try before you go removing and reinstalling the crank, which will just further contribute to the problem on a square taper mount.

  29. #29
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    That's sounds like a good idea Procter. I'll keep you guys posted.

  30. #30
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    You risk having the chain jam between the big and middle rings during a downshift. It could work and it's worth a try.

    This thing is for sure a square taper and not an octalink?

  31. #31
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    I'll go with putting a bb spacer. You need to have the correct chain line anyway. The illustration below shows a different type of bb compared with what you have, but this shows you where to correctly put the bb spacer.

  32. #32
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    OK, I think I fixed it. After careful observation, I noticed that itís just one particular lifter pin thatís causing the problem. It sticks out just a tick farther than the others on the chainwheel. So I took a diamond file and ground it down while at the same time gave it a little beveled ramp for the chain to slide off of. Just enough to keep the chain from grabbing it, but still save the function on the pin. In the 4th picture you can really see how close the chain is to it when on the smallest cog. Everything seems to be working on the stand. Will spin it around the block it tonight.
    Attached Thumbnails Attached Thumbnails Torqued my crank bolt, now this is happening . . .-chain-1.jpg  

    Torqued my crank bolt, now this is happening . . .-chain-2.jpg  

    Torqued my crank bolt, now this is happening . . .-chain-3.jpg  

    Torqued my crank bolt, now this is happening . . .-chain-4.jpg  


  33. #33
    > /dev/null 2&>1
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    Nice fix, putting this in my problems & solutions file

  34. #34
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    Quote Originally Posted by LyNx View Post
    That's called cross chaining, don't do it, simple as that.
    You can safely use the middle ring with whatever cassette cog you want.

    It might not be "as ideal as" using the big ring and the little cog, but converted 1x setups that started as 3x setups all over the world are using every single cassette cog with the middle ring.

  35. #35
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    Quote Originally Posted by Alias530 View Post
    You can safely use the middle ring with whatever cassette cog you want.

    It might not be "as ideal as" using the big ring and the little cog, but converted 1x setups that started as 3x setups all over the world are using every single cassette cog with the middle ring.

    True^ but a 1x setup isn't dealing with interference from another chainring. Most 3x's can use the whole rear cassette but if there is a large tooth count variance between the middle and large ring it makes it tough, and in some (rare) cases impossible.

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