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The lockring on the bottom bracket keeps loosening up, it's now ~15-20km. What can I do to prevent it?

The steeper the hills I ride the quicker it comes undone - it's a single speed so it's clear and I guess expected that the higher the forces the quicker it will loosen up.

UPDATE: I have lockring tool which I use on my commute rides which is wrong size. The lockring was tightened by bike mechanic 2 weeks ago using a proper tool, but it came loose within 30km.

UPDATE 2: When the lockring becomes loose it causes a click in the BB. If I push the left pedal it will click and then if push the right pedal it will click again. In other words, if I put one of the pedals up I can make the BB click if push/pull the crank towards/away from the seat tube.

UPDATE 3: After I removed the cranks and the locking, it turned out that the non-drive side BB cup is not tight in the BB thread. I really mean the cup, not the spindle. Even when the cup is fully screwed in (so the spindle turns freely but doesn't have any wobbles) I can move the cup up/down/left/right. It's a tiny movement, but it's observable and visible to a naked eye. It's as if the cup is of wrong side. The threads on the cup and inside the BB look ok, but I haven't cleaned them yet.

If I put locking on the removed cup it also isn't tight. It seems it fits, but there is tiny sideways movement.

I don't think this related but after removing the non-drive side cup I still cannot remove the spindle which I think is unusual.

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    How are you tightening it? The lock ring should use a proper tool - looks like you're munching the notches by hitting it with a cold chisel+hammer ? Last resort might be some blue locktite. – Criggie Oct 26 '16 at 23:51
  • I have a lock ring tool but it's wrong size :( The thing is that it was once tightened by a bike mechanic using a proper tool and it lasted a bit longer but still loosened up. – tymtam Oct 27 '16 at 1:14
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    @Criggie - What did you interpret to indicate that he has the wrong size lock ring? – Daniel R Hicks Oct 27 '16 at 2:07
  • Is the BB cup loosening up, or just the lock ring? It seems odd to me that you'd even notice the lock ring becoming loose by itself. – Daniel R Hicks Oct 27 '16 at 2:09
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    One suspects that the lock ring is "glued" to the cup somehow (possibly due to some Loctite on the threads), and tightening the lock ring tightens the cup. If it were only the lock ring coming loose then the bearings wouldn't get looser, and tightening the lock ring would actually loosen the bearings very slightly. – Daniel R Hicks Oct 27 '16 at 20:57
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If it's coming loose so soon after being actually tightened fully, then it's probably one of these 2 things:

  1. The lockring threads are gone or in poor condition, probably suggesting they were that way before or as a result of the last time someone tightened it. The easy fix if this is all that's going on is a new lockring. Most bike shops should have a stray one. They're standard sized.
  2. Some kind of binding or other bearing issue is going on inside the left BB cup that's causing the spindle rotation to turn the entire cup in the loosening direction. Normally how it's supposed to work is the spindle is turning counterclockwise, which makes the ball bearings orbit counterclockwise but individually spin clockwise, transferring forces to the cup in its tightening direction. (Hence why ISO right cups are reverse threaded, and also why Italian right cups are notorious for coming unscrewed.) A retainer installed in the wrong direction may be able to cause this, in addition to chewing up the BB.
  • Re: "Italian right cups" - the bike is a Pinarello (made in Taiwan). – tymtam Oct 28 '16 at 0:19
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    It may be Italian threaded then, but I don't know the story with that on Asian Pinarellos. Usually the right cup has its size stamped on the outside that you can check (36x24 is what you're looking for). Even if it is Italian, that wouldn't normally lead to issues with the left cup or lockring coming loose. All told it sounds like something may be up with the bottom bracket. – Nathan Knutson Oct 28 '16 at 2:03
  • After taking the cranks off, it turns out that the non-drive side cup is wobbly :/ I really mean the cup, not the spindle. I can move it with my fingers in all directions (it's a small movement but an easily observable one) – tymtam Jan 4 '17 at 13:03
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I had the same problem once. I figured out that only the left one would come out no matter how much torque I would give to the bolt. So I went to the bike shop and he asked me if I had replaced it and I anwered yes (because I had). So be told me that this can happen because the bolt on the left side can loosen as it loosens as you ride. So he glued the bolt inside with enough torque and told me to leave it like that for about a day. After that no problems what so ever! (Now if I want to remove it I can but I will need some more torque, it's not that it will never come out again...)

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