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I'm replacing the crankset and bottom bracket on my old steel frame road bike, which looks like this one, so I'm guessing it's from around 1985. I picked up a 68 mm square taper bottom bracket and found that I couldn't fit the non drive side bottom bracket cup in. The drive side is fine, but the other one can't fit in at all, even with all the other parts removed (to ensure nothing was getting in the way). The old one (from a cottered crank) fits in fine and rotates without problems, and there doesn't seem to be any deformation or damage. Do I simply have the wrong part? Is the possible the part is defective?

Here is a picture of the bottom bracket. I don't have calipers so I couldn't get a decent measurement, but the left cup seems bigger, and the pictures seems to confirm this.

Bottom Bracket

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  • First, does the cup not fit at all, or does it simply not thread in all the way? If it doesn't fit at all, have you verified that the threads on both cup and bracket housing are right-hand? Where did you get the new BB from?
    – Daniel R Hicks
    Commented Jun 22, 2013 at 17:53
  • I can't even fit it up to where the threads engage. There's a short (1/4 inch?) non threaded part, which, just barely, doesn't fit in to the bike. Also, the bottom bracket has cups on both sides, which is different from this video where they state the drive side should be permanently affixed.
    – Kibbee
    Commented Jun 22, 2013 at 17:56
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    Actually, having the drive side cup permanently fastened to the cartridge is a bit of an aberration, but a common one, since that's how Shimano generally does it. But you may have to find a different cup at your bike shop or wherever. (Does the right cup have the same unthreaded section?)
    – Daniel R Hicks
    Commented Jun 22, 2013 at 23:25
  • @DanielRHicks The right cup does not have an unthreaded section. The left cup, does not fit in either side, and the right cup appears as thought it would fit in the left hand side, but it of course won't go in because of the reverse threading.
    – Kibbee
    Commented Jun 23, 2013 at 0:00
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    Was the box opened? My guess is that they took several BBs out of their boxes, trying to fit a bike, and put the wrong cups back in the wrong boxes. What you have on the left is probably a French or Italian cup.
    – Daniel R Hicks
    Commented Jun 23, 2013 at 13:48

2 Answers 2

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So I took it back to the shop. Turns out that something got messed up at the factory/supplier, and the left hand cups on a bunch of their English bottom brackets was actually Italian, which means they were larger and wouldn't fit.. There were able to find the proper size cup from a bottom bracket with a difference spindle length. But they opened 2 or 3 other boxes and they all had the same problem. They were quite thankful to me to alerting them to the problem.

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Is it possible that you bought an Italian threaded bottom bracket for an English shell or vice versa?

For the two scenarios above, compare the two cups of each bottom bracket to themselves (ie old to old, new to new) by placing them outside down on a flat surface. Now look at the threads. Do they pitch in the same direction or opposite? If the threads pitch in opposite directions then you have an English bottom bracket, which is more common. If they pitch in the same direction, you have an Italian bottom bracket, which is less common, but can be mistaken for English as the drive side cup has the same pitch and TPI as an English drive side cup- the width is just a little different. Here's the best ASCII diagram I can muster:

Italian drive side
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Italian non drive side (same thread direction as drive side)
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||/////|
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----------------------

English drive side
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English non drive side (opposite thread direction as drive side)
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||\\\\\|
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It would be easy to mistake an Italian BB for an English one (or the other way around) as the drive side cup would thread in fine and the width is very similar. Once you get to the non drive side is where you would run into trouble, which matches up pretty well with the problem you described.

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  • It's definitely English, as the right thread is left hand, and fits in, but I'm beginning to wonder if the left hand cup is Italian, as Sheldon's site says that Italian cups are 36mm, which is slightly bigger than 1.37 inches, which is 34.8 mm.
    – Kibbee
    Commented Jun 23, 2013 at 0:20
  • What I was trying to illustrate above is that both English and Italian drive side cups are left thread.
    – joelmdev
    Commented Jun 23, 2013 at 1:05
  • Correct me if I'm wrong, but just to clarify, on English threads, the drive side is left threaded and the non drive side is right threaded. On Italian, both are right hand threads. Where "right hand threads" is standard threading where turning clockwise tightens the part. Since the bb cup that doesn't fit is on the non drive side, both Italian and English would be right hand threaded on that side.
    – Kibbee
    Commented Jun 23, 2013 at 1:15

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