Confused about bottom bracket cups

Manc33
Manc33 Posts: 2,157
edited October 2014 in Workshop
I have a Shimano UN-55 bottom bracket on my bike, I have rode hundreds of miles on it already, but the way it is on the bike doesn't seem right, as if the cups are the wrong way around!

The BB cup on the drive side has quite shallow holes, the BB cup on the non-drive side has much deeper holes where you can get way more leverage to tighten it. Surely that isn't right? I mean you can tighten up that non-drive side one a lot easier than the drive side one?

Its a British thread so the drive side cup screws in anti-clockwise and the non-drive side cup screws in clockwise.

The problem is that the cup with the deeper holes is on the non-drive side, not the drive side, surely you tighten the drive side up real tight, then screw in the non-drive side cup tight enough after that? I mean it must be the drive side that needs to be the really tight one because the chain on the biggest chainring causes far more flex on that side than on the left side thats just a crank arm?

I just wonder if its possible to be riding around on it with the cups screwed in the right way (they are screwed in the right way) but the cups themselves are swapped around? That is impossible, right? :oops:

Whats annoying is I can't get anything like the same leverage on the drive side cup as I can on the non-drive side!

I wish I had a vice to just rest the whole bike on top of the BBT-22. :roll:

My cups did come loose a few weeks back, because I can't tighten the drive side as tight as the other side.

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That left cup above has the deeper holes - but is it the drive side cup, or non drive side?

Is that bottom bracket above turned in the pic so if it was on a bike you'd be behind the bike on the non-drive side?

It has a "normal" thread on that cup.

Has there ever been a case where the BB shell itself gets manufactured the wrong way? :lol: Imagine how odd your frame would have to look. Well I mean the threads done the wrong way.

It does have "L" and "R" on the bottom bracket, but that means nothing because it doesn't say if thats looking from behind the bike or in front of the bike. :? Essentially there isn't a left or right when you could be standing in front or behind something. They should put "DS" and "NDS" :x I can only guess it assumes you're sat on the bike lol, who knows.

Comments

  • imposter2.0
    imposter2.0 Posts: 12,028
    edited October 2014
    The BB only fits one way, if that helps. As for the 'L' and 'R' - just think in terms of your left and right legs......while facing forwards on the bike, obviously.....
  • Manc33
    Manc33 Posts: 2,157
    Imposter wrote:
    The BB only fits one way, if that helps.

    It is in right, but how come the holes aren't as deep on the drive side cup?

    Do I just need a £30 bottom bracket as opposed to a £10 one or something and it will have deep holes on both sides?
  • imposter2.0
    imposter2.0 Posts: 12,028
    I don't know what 'holes' you are talking about.
  • Manc33
    Manc33 Posts: 2,157
    edited October 2014
    Imposter wrote:
    I don't know what 'holes' you are talking about.

    The 20 slots. The holes for the BBT-22 tool to go into.

    The old way was better where the BB had 3 holes and the tool had 1 pin, it could slip out, but not like these bloody things can. Pretty much impossible to tighten it up without putting the BBT-22 in a vice. Not just any vice but one with acres of space around it. :roll:
  • imposter2.0
    imposter2.0 Posts: 12,028
    The tool is a taper fit in the slots - some tools fit better than others. Co-incidentally, I removed one of these from a frame tonight - I have three different brands of tool for those BBs and some fit better than others, depending on whether the BB is a Shimano, or pattern part...
  • Manc33
    Manc33 Posts: 2,157
    All I know is the old way didn't potentially require a vice. A wooden hammer and good luck maybe. :lol:
  • dj58
    dj58 Posts: 2,221
    Did you clean out the BB threads and lubricate them with grease/anti seize before fitting the cups, and did you start the cups by hand before using the BBT-22 tool to tighten them fully?

    If you are having difficulty tightening the DS Right hand cup, having to use excessive force, then it could be cross threaded. Does it make contact with the BB shell face? Have you tried removing it and inspecting the threads for damage, you BB may need facing and/or the BB threads may need chasing through.

    The last time I fitted one of those BB's using the genuine Shimano tool TL-UN74-S I don't recall either of the cups being particularly difficult to tighten up.
  • k-dog
    k-dog Posts: 1,652
    These BBs shouldn't be difficult to install - plenty of grease, screw in the fixed cup (the R one in your case) so it is flush against the frame, then screw in the adjustable cup to 40Nm - which is pretty tight.

    Done. I think you're overthinking it. The removeable cup doesn't really tighten against the frame - but it tightens against the fixed side which loads everything evenly.
    I'm left handed, if that matters.
  • Manc33
    Manc33 Posts: 2,157
    So the non-drive side is what's actually keeping it tight?

    Thing is if you screw the non-drive side in tight (say 40nm) and you could only manage to get the drive side up to say 25nm, what then? Isn't the non drive side going to make the drive side fully loose again?
  • Sometimes the non driveside splines are deeper because he cup itself is just silver coloured plastic, not metal
  • keezx
    keezx Posts: 1,322
    I've used these things many years and no one ever came loose, really idiotproof.
    The lefthand thread on the driveside prevents coming loose, you must be doing something terribly wrong.
  • Manc33
    Manc33 Posts: 2,157
    The last one I took out of a bike had a plastic cup, but it had splines as deep on the drive side as well I am sure. Had no problem taking it off. Some cheap Kinex thing, like £6 new.

    Not sure what 40nm really feels like by hand, really tight, but I have never had a cassette lockring come loose and I do that by hand just the same way as I would do the BB, I mean just as tight.

    A vice would be ideal and I can see why every bike workshop has one. Resting the entire bike on a vice, it wouldn't matter if it slipped, you're not bashing your hand into something with the force of 40nm. :roll:
  • imposter2.0
    imposter2.0 Posts: 12,028
    As others have said, none of this should be particularly difficult. Put the drive side in first, nip it up and then screw in the NDS cup. I don't have a torque wrench and work on the 'that's tight enough' principle - which hasn't let me down yet...
  • desweller
    desweller Posts: 5,175
    It's unlikely to have been made incorrectly.

    It is easier if you can lay the frame on its side at waist level, e.g. on a workmate, but not essential. You should be able to comfortably exceed 40Nm with a BB spanner.

    Using these tools does require a little refinement of technique though; concentrate on keeping the tool square in the BB and you should not have any problems.
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