Is this why ???????

redvee
redvee Posts: 11,922
edited April 2008 in MTB workshop & tech
My lefthand crank keeps coming loose?

th_44357_DSC00582_122_373lo.JPG

Got a new c/set sorted, looking at a BB on Ebay and need to sort a c/ring. Carrying a toe strap and allen key with me so coming loose on way to work not a major issue, commute only 1.5 miles.
I've added a signature to prove it is still possible.

Comments

  • supersonic
    supersonic Posts: 82,708
    Have a read of this:

    http://www.bikeradar.com/forum/viewtopic.php?t=12564509
    GT ZASKAR CARBON TEAM

    VOODOO CANZO

    Come and see me at https://www.facebook.com/biketyke/
  • god1406
    god1406 Posts: 554
    ouch. That must have taken a fair whack.

    And a crack like that would mean you can't tighten it properly, or if you did it would work loose easily.
    Rocky Ridge

    Stuff
  • redvee
    redvee Posts: 11,922
    edited April 2008
    Yes, time to retire the crank and tapered BB, they've both been through many bikes over the years :)

    Not taken a whack, though using a 3 foot extension on the allen key might somehow explain the crack.
    I've added a signature to prove it is still possible.
  • supersonic
    supersonic Posts: 82,708
    Ah. see the crack now on the close up!
    GT ZASKAR CARBON TEAM

    VOODOO CANZO

    Come and see me at https://www.facebook.com/biketyke/
  • nicklouse
    nicklouse Posts: 50,673
    grease on the taper does that as well.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • supersonic
    supersonic Posts: 82,708
    You a dry fit man too Nick? Same here. been involved in a few 'discussions' about this one. Clean 'n' dry for the tapers me thinks!
    GT ZASKAR CARBON TEAM

    VOODOO CANZO

    Come and see me at https://www.facebook.com/biketyke/
  • nicklouse
    nicklouse Posts: 50,673
    dry is what all the makers say for the old square taper.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • The Big Cheese
    The Big Cheese Posts: 8,650
    sorry for hijack but this is very interesting re: grease.

    Is it only square taper that you do not apply grease to? Or all, I have been greasing my HTII's axle when assembling?
  • nicklouse
    nicklouse Posts: 50,673
    try reading the links in my sig.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • redvee
    redvee Posts: 11,922
    Few more pics, not sure if these are new. Just need the postman to do his bit and deliver my BB.

    th_92077_DSC00585_122_933lo.JPGth_92082_DSC00586_122_402lo.JPGth_92088_DSC00587_122_514lo.JPG

    Got no trust in the bike at the mo. Limiting myself to 1 mile rides at the mo :(
    I've added a signature to prove it is still possible.
  • Rockhopper
    Rockhopper Posts: 503
    Cheesey, its a taper fit, greasing it can allow it to slide too far along the taper and crack it.

    Most of the other types of crank/BB are not taper fit.
  • John Stevenson
    John Stevenson Posts: 962
    Funny, I have been greasing tapers for 20 years with exactly no problems.

    The way to get a crack like that is to repeatedly tighten the bolt.

    Square tapers are light (I think some combination of a Middleburn crank and one of the better titanium-axled bottom bracket units is still the lightest crankset you can buy). But they have problems, one of which is that as you ride them, the crank 'walks' up the taper.

    You can see this because the bolt becomes loose, and there's fine powder in the joint produced by the two surfaces fretting against each other.

    If you then tighten the bolt, you push the crank up the taper some more. Rinse, repeat crack.

    It's immaterial whether the taper's greased or not in this process.

    However, what greasing tapers allows you to do is to correctly tighten the bolt in the first place, because, with the friction thus reduced, you'll get an accurate reading from a torque wrench.

    If you've never used a torque wrench to fit a crank, try it sometime. 35-50Nm is startlingly tight. I suspect a lot of failures of this joint are down to people tightening it with an 8mm Allen key and just not getting it tight enough.

    Once you have it tight in the first place the trick is to leave it alone.
    John Stevenson

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