How does a bottom bracket cup tighten if...

Manc33
Manc33 Posts: 2,157
edited August 2014 in Workshop
I have an English thread bottom bracket shell, where the drive side has a "reverse" thread and the non-drive side has a normal thread.

This means you screw both bottom bracket cups into the shell by turning the cups "backwards".

Here's the part I can't understand - if both cups are screwed backwards and you're pedalling forwards, how do the cups stay tight or as some say "should tighten up if anything"?

My BB cups came loose last night, when I was screwing them back in as tight as I could I realized pedalling looks like it would unscrew them, not tighten them.

I have got the BB in the right way lol. The cup on the non-drive side and the main BB and other cup on the drive side.

Maybe the way its setup with a bar in the middle (the axle) it tightens it up but it just looks odd.

Its lucky that came loose near home because I tend to not carry a BBT-22 with me. :lol:

I don't think I can even get the leverage to make the cups tight enough, that stupid chain whip tool with the 1" hex (SR-1) doesn't help, you can't press against a square piece of metal with 35nm on your hand. :roll:

Comments

  • JayKosta
    JayKosta Posts: 635
    The bearing in the BB act as 'idler gears' which reverse the direction that the force is applied to the bearing cups from the spindle.

    Does your BB have a 'lock ring' on the non-drive? On typical cup-and-cone BBs, the non-drive cup is adjusted to make the spindle turn freely with just a tiny amount of wiggle or 'shake', and the lock ring is tighten firmly against the BB shell to firmly hold the cup in position.

    Jay Kosta
    Endwell NY USA
  • Manc33
    Manc33 Posts: 2,157
    JayKosta wrote:
    Does your BB have a 'lock ring' on the non-drive?

    No, it just sticks up a bit over the one on the drive side.

    With it being a new frame it might need the BB shell re-facing.
    JayKosta wrote:
    On typical cup-and-cone BBs, the non-drive cup is adjusted to make the spindle turn freely with just a tiny amount of wiggle or 'shake', and the lock ring is tighten firmly against the BB shell to firmly hold the cup in position.

    Nothing locks, its just a standard UN-55 square taper bottom bracket.

    Which side should be screwed in tight first, the drive side I assume?

    Is this the right way:

    1. Screw in both cups finger tight.
    2. Screw in the drive side to full torque.
    3. Screw in the non-drive side to full torque.

    It has taken about 300 miles to come loose.
  • keezx
    keezx Posts: 1,322
    A cartridge bottom bracket coming loose is certainly not normal.
    Never ever happened to me in 25 years using these things....
    I would inspect the threads in your bike carefully, are they worn out?
    Is your BB still 68 mm wide?

    About the job: always righthand first full torque, then lefthand full torque (not much required)
  • Manc33
    Manc33 Posts: 2,157
    Yeah it is 68mm. Was never a full bike though... bought as a frame and built up.

    It was just never in tight enough to start with, I was probably all paranoid with it being carbon when installing. :oops:
  • k-dog
    k-dog Posts: 1,652
    One word: precession.
    I'm left handed, if that matters.
  • pinarellokid
    pinarellokid Posts: 1,208
    Apply a little thread lock that will sort it out for you
    Specialized S Works SL2 . Campagnolo Record 11spd. rolling on Campag Zonda wheels

    http://app.strava.com/athletes/881211

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