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    BB replacement wont screw in flush with frame (drive side).

    I am working on and old (1991 I think) Peugeot mountain bike. The original is a 68 122.5 bottom bracket as far as I can tell. I have bought a Shimano BB-UN300 to replace it. It screws in easily, can get it in without any tools, however it 'bottoms out' with about a 5mm gap. The non drive side does this also but I have read that it is not so much of an issue for the non drive side, however drive side should be flush with the frame. If I had to guess it seems like the threads on the frame don't go in far enough to accommodate the BB.

    Any insight would be greatly appreciated!
    Cheers.

    by 2goodenough

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    6 Comments

    2. Cyrenetes on

      The drive side should be torqued down first before the left side is in, the left cup shouldn’t ever “bottom out” in the frame because when installed it presses against the cartridge, not the frame. If that’s what you were already doing, I don’t know what the problem could be.

    3. WingChuin on

      I always install the left side a quarter way first to setup as a guide to keep the bb straight. Sometime the cable guide pin or screw is in your way, pop it out for now. If that’s not the case, you may need to visit your LBS to have the bb threads rechased.

    4. Fizzyphotog on

      You have some awful rusty looking threads. You can see where the old one didn’t go all the way through the threads and left some to rust, your new cartridge is probably hitting those and binding up. Run a wire brush in there and polish them up. Are you using a little grease on the threads, anti-seize if you have some? And yeah, it takes lots of torque to get it all the way in. If the same type came out, you know a new one should go in.

    5. Lollerscooter on

      does your bottom bracket come with that blue stuff on the threads that shimano apply? .. I had the same problem as you and it turned out, the blue stuff takes op too much space/is too hard/doesn’t compress.. so it was REALLY hard to thread it in.. the problem was especially where the cup goes over the bearing cassette itself.

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