Stripped bottom bracket threads

[Efrogwr]

I have an old mountain bike (aluminium frame) with a 73mm bottom bracket. The NDS thread is stripped/worn so much that the locating ring for the bearing cartridge is a loose push fit... I can't find a 73mm threadless bb cartridge. I suspect that the frame is worn too much to make trying to retap the thread worthwhile.

I welcome your comments and reccomendations.

[mrcharly-YHT]

You could glue a replacement in with epoxy metal putty.

I distorted the shell on a Mercian so much that even a Prestige threadless BB wouldn't stay in. In the end I put epoxy putty in there, sanded it out until the BB fit.

Smeared some epoxy putty in so that it was just proud of the threads, then let it set until it was only just possible to indent with a thumbnail, then screw your BB in place.

That BB isn't going to come out in a hurry, so take care about how you do it. Epoxy softens with heat so it would be possible to remove it, but it would take determination.

[Dave_C]

a related Q popped up elsewhere and someone recommended Praxis or Wheel Manufacturing adapters. Glue these in and fit a narrower BB?

Dave C

[bikepacker]

Argos Cycles in Bristol have a couple of solutions. They did a good job of repairing the BB on my Super Galaxy.

[Torslanda]

Strip it back to a bare frame. Have a machine shop narrow the shell to 68mm - from BOTH SIDES - and fit a threadless conversion or narrowed to 70mm and rethread it to take an Italian BB.

If you decide on the latter make sure the cartridge you want is available in that thread...

[mzjo]

Strip it back to a bare frame. Have a machine shop narrow the shell to 68mm - from BOTH SIDES - and fit a threadless conversion or narrowed to 70mm and rethread it to take an Italian BB.

If you decide on the latter make sure the cartridge you want is available in that thread...

Swiss might be even better than Italian, the threads are left and right handed like British, whereas Italian is right handed both sides (like French). I don't know about the availability of Swiss bbs though.

[LittleWheelsandBig]

I've only ever worked on a couple of bikes with Swiss threads. Italian threaded components are a lot easier to find, particularly for anything made in the last thirty years.

[Brucey]

aluminium frames are not 'for ever' anyway; I'd just use standard epoxy resin to bond a cartridge BB into the frame; if you choose well the BB could outlast the frame.

If you want to make it serviceable, choose a BB with a RH cup that can be removed, so that when the bearings fail, you can leave the RH cup in the frame and change the rest.

To fit a BB with epoxy resin, there is no need to faff about putting on layers and then sanding them down; just clean everything up and bung it in there with the glue coating both surfaces; job done.

If you want to later remove a part that is bonded-in with epoxy, just heat it to about 150 degrees and the glue will soften enough that it will come out using the normal tools.

cheers

[Efrogwr]

I got round to doing the repair three weeks ago, following Brucey's advice.

It worked well; the bike is now rideable.

Thankyou to all who replied with advice, espacially Brucey.