Crank arm keeps coming loose

danielsbrewer
danielsbrewer Posts: 123
edited January 2012 in The workshop
I have a Kona Jake 2010 and in the last few months the crank arm keeps coming loose, making the whole peddling mechanism wobbly until I tightened up the screw bit. Here is a photo of the bit that comes loose (apologise for the bike being so dirty, rush job):

6646199635_1387e3d5bc.jpg

They are FSA Omega crankarms. I have taken the crank arm off by undoing the two side screw and the large central one. Cleaned everything, then put a bit of grease on each of the three screw, tightened the big screw then the two side screws. Despite this it still comes loose after a few weeks. Has anyone got any ideas what I am doing wrong or wheather something is going wrong?

Second question! I have used so much force on the large central screw that I have managed to munge the allen key socket, any ideas what that large wide screw is called so I can get a replacement?

Many thanks

Comments

  • danielsbrewer
    danielsbrewer Posts: 123
    This http://www.jejamescycles.co.uk/fsa-gamma-drive-omega-mega-exo-left-hand-crank-bolt-id39743.html looks like it answers my second question. Does that seem right? A FSA Omega crank bolt.
  • The Rookie
    The Rookie Posts: 27,812
    Greasing the lock bolts was a bad idea, you want friction on the threads, how tight are you doing the 2 lock bolts (the ones across the arm) like the stem on the steerer, once those are tight the compression adjusting (big one on the end) bolt is redundant.

    Simon
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • danielsbrewer
    danielsbrewer Posts: 123
    Well with increasing tightness, this time tighter than before. So the idea would be to do up the lock bolts very tight ( I will remove the grease next time!) and the big one not that much. Also should you tighten the big screw or the lock bolts first?
  • nicklouse
    nicklouse Posts: 50,675
    preload the bearings first. Big bolt and then lock into place with the lock bolts.

    see Parktools.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • The Rookie
    The Rookie Posts: 27,812
    Noting that if you don't load the bearings right the arm will work loose as it seats in the bearings even if the clamp bolts stay done up tight........suspect from what you now say that that was your issue, it wasn't the bolts but the spanner...the old holding the allen keys.

    Simon
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.

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