Bottom bracket threads stripped on a 27.5 mtb frame-
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  1. #1
    mtbr member
    Join Date
    Feb 2018

    Bottom bracket threads stripped on a 27.5 mtb frame

    Hi all,

    I'm looking for some advice on my 2016 Voodoo Hoodoo 2016 frame. Due to a poorly installed bottom bracket I am left with cross/stripped threads in my frame when trying to install a new BB. I have a local engineering firm taking a look to see if they can rethread later in the week however I'm just investigating options if they can't complete this. I have seen on the web some threadless bottom brackets but them seem to be all in the 68mm shell width and not 73mm (which is what I require 73mm x 118mm). I have read about people that have machined down there frame to fit the 68mm shell size? So maybe this is another option then buy the threadless BB?

    Any help gladly received.
    Many thanks

  2. #2
    Super Moderator SuperModerator
    Reputation: driver bob's Avatar
    Join Date
    Oct 2005
    Any good shop will have frame taps.

    If the threads aren't completely mashed then running the taps through can clean up existing good threads and cut through/square off bad threads.

    We've saved a number of frames over the years when this happen.

    What it can't do is make new threads if the whole side of the frame has been cross threaded all the way through.

  3. #3
    mtbr member
    Reputation: J.B. Weld's Avatar
    Join Date
    Aug 2012
    I'm not sure how you would turn a threaded bb into a threadless one. You don't need an engineering firm, as mentioned above just take it to a shop and have them run some taps through it. Post a pic if possible.
    I brake for stinkbugs

  4. #4
    mtbr member
    Reputation: Redlands R&C's Avatar
    Join Date
    Dec 2013
    Try what driverbob suggested first. I had a customer who used a cheap BB-tap tool on a brand new Soma Wolverine, but he did it backwards! So I told him I'd give it a shot with the Campy BB tap (oooooooh), but didn't guarantee anything. It worked out great in the end.
    Barring that, if that engineering firm/machine shop will narrow your BB shell to 68mm from 73 (I'm assuming, I haven't looked at your specs) you can run this guy and square taper cranks. I've used a fair amount of these in my time at the non-profit shop.
    Silly bike things happening.

  5. #5
    Most Delicious
    Reputation: dr.welby's Avatar
    Join Date
    Jan 2004
    You can tap the frame up to Italian on the stripped side and mix and match the needed parts from UN55 bottom brackets, or just tap up both sides. Italian threads are a little bit larger in diameter so they taps will cut into fresh material. But for sure try running a BSA tap through there first.

    Italian BBs are 70mm so you might have to dig up an old UN-xx left side that doesn't have the bottom-out stop.

    If you can find and older Shimano bottom bracket that has removable cups on both sides you could probably space it on the drive side with a thrust washer between the bearing unit and the shell.

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