Crankset/Bottom bracket issue

Forums Mountain Bike Forum Crankset/Bottom bracket issue

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    • #117286

      Good morning all,
      I own a Trek Cobia from 2011. It has a Octalink BB and a Shimano Alivio crankset with a Sram X5 shifter…OK. What happened was the bolt that holds the non-drive side crank arm to the BB came out and eventually the crank worked its way off. I was riding the bike at the time and the crank spun around wearing the teeth in the crank arm against the BB splines. Then i sent to my LBS to get a bolt (incorrect bolt but it worked) put back in and it worked for a while. Eventually the non-drive side crank loosened again. This time i caught it and found the correct bolt and put it in and torqued it down. Again i went riding and the non-drive side crank arm started loosening. I then changed the BB to a V2 Octalink (which apparently had a bit shorter splines then my original). Since it moved my front derailleur in i had to adjust my front derailleur. So then i put my crank set back on and torqued it down. I had to remove a little metal from the non-drive side crank arm to keep it from bottoming out against the frame/BB. I torqued it all down with a little blue locktite. I rode 15 or so miles the other day and the crank loosened again. I had to tightening it 3 or 4 times during the ride. This time i went back to the LBS and got a new crank, a Shimano Octalink. It appears to be the same size as my old…I install it and torqued it all down. Now the L and H limit screws are maxed out and seems that there isn’t enough travel to adjust it correctly. Could this be? Sorry this is long…any help would appreciated…

    • #117287

      Hehe, I had problems at first following the course of the question.

      "bottom bracket, bottom bracket, bottom bracket, crank arm, bottom bracket, DERAILEUR!!"

      Not all deraileurs(or shifters) will work with all cranksets. It sounds to me like you have wider ring spacing on this new set that will require another deraileur. If you compare the ring spacing with a micrometer or by holding up against each other, do the rings look identically spaced?

    • #117288

      Yeah…the issue is hard for me to follow too and even more difficult to put into words. From what i can tell the two chain rings are spaced the same. I just don’t see how it would cause the front derailleur to have to max out each limit screw. I thought maybe my shifter sequencing was off somehow (can that happen?). I wish that I’d have just replaced it with the exact same crank…finding it on line was cheap and easy. I’m gonna take the bike to my LBS on Tuesday to see what they can do.

    • #117289

      Check the chain line measurement spec for each crank. There are differeent sizes. I went from a 47 to a 50 mm and had to realign my FD so that it shifted correctly. Those 3 mm made a huge difference

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