New Shimano drivetrain feels tight

Discussion in 'Cycling Equipment' started by Threshold, May 24, 2010.

  1. Threshold

    Threshold New Member

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    About a week ago, I went out riding with my usual group of friends and my original crank finally decided to fall apart.

    The history:
    The crank that I had was the FSA SL-K carbon crank and after doing a lot of research as to what happened, it seems to be a common problem with this brand of crank. While I was riding, I found it weird that I couldn't get the chain to get up on the big ring, so we pulled over and check out what happened and the bolt that hold the crank together (and also the left crank arm) was completely loose. We slowly went back to my friend's house, took the whole thing apart, cleaned, greased, and put everything back together. Started to ride and everything seemed ok until about 10 miles later, where the same exact thing happened, but this time I brough with me the 8mm allen key just in case. So I went to go tighten the bolt and it would just spin and spin. And even with the bolt in place, for some weird reason, the crank arm would just slide right over the bolt and pop out freely. The only thing that was hold it in place was my legs and feet because they were attached at the pedals... lol.

    So anyway... after doing the research and seeing the problems the FSA cranks have, I decided to go with Shimano Ultegra 6700 series compact crank, BB, chain, and pedals. Chain and pedals were a gift to myself since I found them for cheap... lol. So we put everything together and we gave the crank a push in reverse to see how smooth it was and it would only make it about 1/4 to 1/2 turn before stopping, where as my friend, with the same setup, would do about 1.5 turns before stopping.

    Next day, I went out for a ride and the drivetrain felt so tight and stiff. I felt that I was exerting much more force to keep that pace that I usually kept with the other crank and also got fatigued much earlier than usual. Also... when pedaling, I feel a bit of a slight resonance coming through the pedals to my feet. I read somewhere that that usually means the bearings are bad or really worn down, but this components are brand spanking new.

    What could be the cause of this tightness and non-efficiency?
    1. Do you guys think that the BB might be on too tight? Would that make a difference? We didn't have a torque wrench for the spec torque. I called my one other friend that is pretty handy with bikes and he mentioned that maybe we put the BB on too tight.

    2. Do the BB require a certain amount of miles for break-in?

    I will be ordering a BB tool (3/8 drive) that can be linked to a torque wrench so that we can torque the BB to spec and maybe (hopefully) that will fix the tight issue. Can anyone think of anything else?

    Also... while on the BB tool subject... what does BBT-9, BBT-19, BBT-etc mean?

    Sorry for all the questions and appreciate the help.

    Thank You.
     
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  2. Peter@vecchios

    [email protected] New Member

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    Have a bike shop prep the BB shell and then install to spec.
     
  3. CdnRider

    CdnRider New Member

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    Let us know what the problem turned out to be. For future reference.
     
  4. Threshold

    Threshold New Member

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    I actually already bought the BB tool that attaches to 3/8th drive torque wrench. Once that comes in, we're going to pull everything apart again and reinstall everything to spec torque.

    If that fails to work out, then I will probably take it into a shop to check it out.

    Thank You.
     
  5. Threshold

    Threshold New Member

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    Will do.
     
  6. alfeng

    alfeng Well-Known Member

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    What does this mean? Are you impulsing the crank and letting it spin freely OR are you constantly engaging it while you rotate the crank(s) backwards?

    If the latter AND the crank/chain seems to stop in the same place then there may be a problem with the way you installed the chain -- that is, a binding link.

    You can isolate the chain as being the problem, or not, by putting our old BB & crank on just to see how much resistance is present when the bike is in your workstand.

    A mistake which has been documented in another thread is to have the chain skate on outside of the vestigal tab midway between the two pulley wheels rather than freely passing between the pulley wheels ...

    While it is possible that your frame's BB shell needs to be faced, I really doubt that would be the case ... on the few, random frames -- from a mid-80s steel frame, a 90s vintage steel frame, a new/(raw, unpainted) alloy frame, etc. -- into which I've installed External BB cups, none needed facing ...

    YOU can check to see if your BB faces are square by removing the cups & inserting a rolled up piece of typing paper into the BB shell ... make one edge flush with either face, square the other end of the paper & see if there is any deviance between the face of the shell & the edge of the piece of paper that is inside the BB shell. Repeat on the other side.

    [​IMG][​IMG][​IMG][​IMG][​IMG]BBT-9 (good enough)

    [​IMG] BBT-19 (better)
     
  7. Threshold

    Threshold New Member

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    Wow... that is a lot to swallow... lol. I'm not 100% on all the suggestions that you made there, but I will read it over a few times to get a clear understanding of what you mean.

    As far as making the crank rotate backwards... I just give it one good impulse (as you call it). If I keep constant force on the crank to make it continuously rotate, it rotates the whole time without stopping. The chain does not bind anywhere where it would hinder the crank from continuing to rotate. I know that giving it one good push and seeing how much it spins is probably not a good way of gauging if the drivetrain is smooth, but in comparison to my buddy's drivetrain, I figured it would be some what the same.

    Good thing... I bought that same exact BBT-19 piece... Thank You. Is "BBT" and acronym for something?... maybe "Bottom Bracket Tool"?... but what would the number stand for?

    Bit of a noob here but trying to learn the lingo... ;)

    Thanks.
     
  8. xxtimber

    xxtimber New Member

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    For the GXP bottom bracket it's normal to experience drag when it's first installed. After a few rides, it will smooth out. I remember being shocked with the drag when I installed my first one...I'm not sure if that's the problem here.
     
  9. Peter@vecchios

    [email protected] New Member

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    Remember on a 6700 crank, the left hand arm is tightened only hand/finger tight with the little cap in the end of the spindle, LH crank arm, THEN torque the pinch bolts. BTW-All frames need to be faced, if you wish the bearings to be parallel to one another for smoothest running and longest life.
     
  10. tafi

    tafi Member

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    For the cups to sit parallel the most important factor is that the threads in the BB are axially aligned so that the cups will also screw in straight and also be axially aligned to one another.
    The further you place the bearings apart (ie: for modern outboard bearings), the more critical this alignment is.
     
  11. Threshold

    Threshold New Member

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    I know it's been a while but I finally was able to take everything apart and figure out exactly what was wrong with the BB. For the short answer... it was just simply too tight. It was probably tight to the point that the BB side walls were pressing against the bearings and restricting them from rolling freely, which of course caused major friction against rotation.

    I ended up buying the BB socket tool that you can attach to a torque wrench (TW) and let me tell you, because of this experience, it was defnintely worth buying. Before actually removing the BB from the bike, I set the TW to 30 ft-lb (required by spec) and tried to loosen the BB and it didn't budge at all. I then set it to 40 ft-lb, and nothing. Set it to even 50 ft-lb and it didn't come loose. So finally I just used the normal BB tool and removed everything. I then greased everything up again, along with the mating surfaces of the crank arms to the BB and then torqued the BB to 30 ft-lb and everything rotates freely now. I really got excited about this cause I knew I felt something out of place and I was right... so it feels good to know that I've had enough experience to realize that something just wasn't right... :)

    Again... sorry I took so long to get back to everyone, but I finally had some time to get this done.
     
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