Alloy frame restoration - bottom bracket threads

[jimipolar]

Just wondering if anyone has ever had any success with repairing worn bottom bracket threads on an alloy mountain bike frame.

This bike of mine has been such a fun ride, but it's showing it's age and has developed bad wear in the bottom bracket threads and will no longer hold the cups in place..

Is it time for a new frame? I'd like to repair it if possible.. Any thoughts guys ?








I will get some shots that clearly show the wear n tear Awww..

 

[forest_ninja]

http://www.gripsport.com.au/

Can't recommend Gripsport enough

 

[jimipolar]

Sweet thank you, Gripsport look great! Unfortunately they're aways on XMas holidays till the 3rd week of January - that's just too much Summer to miss out on!

Haha if anyone knows somebody in Sydney who handles this style of engineering / welding please get in touch!

 

[Reubs]

I would think you could pick up a second hand frame in good nick for about the same as it will cost to have your old frame bodged up. I'm sure it's possible to repair but due to the fine nature of a BB thread, there isn't going to be much meat left of the welded new bit. I've had frame repairs done at a local 4x4 bullbar shop in the past. They may be able to fill it all in then you take it to the LBS to tap the thread in. You'll have to ream (or file if you must) after welding to get the bb shell back to the right size for tapping.

 

[miko]

Yeah, I suspect you'd want to really love the frame if you're going to repair it. It's a bit of a pain in the arse job...

 

[boyracer]

Can you get Italian thread externals? it's a slightly deeper pitch, so you can recut the threads in a fubar english frame.
could work. Any 'roadie' shop would have an italian cutter.

 

[miko]

What sort of BB's will that limit him to though?

 

[boyracer]

Italian.
better than not riding?
he can still gripsport it when they reopen.
I'm in Adelaide and have It. cutter.

 

[Fatherpaul]

I assume you have tried various bb cups to check.

I always use plumbers teflon tape on mine to keep them secure. They never come loose this way. You could try it. Depends on the bike and cups but with normal threads and cups i use about 2 to 3 turns of the std white tape. Remember to turn the tape onto the threads in the direction of tightening the cups. There is also the plumbers gas tape which is thicker than the std white tape which may be an option.

 

[jimipolar]

So i got in touch with a couple of specialist bike builders who have had experience with this in the past. Gripsport were great to talk to and have the expertise to do a fine job. Located in Melbourne tho and part of me wants to establish a connection with a local frame builder for any future projects. I have been following Primate frames for a while, i found them on Pinkbike a whiles back. Got in touch with them too. The process is difficult, but not for an engineer with the right tools. Basically it goes like this. Strip the bike down, so the frame can be manoeuvred easily in the jig. The bottom bracket shell gets machined out to a certain degree, leaving the integral strength of the walls intact - as best can be. An insert from steel is then machined to fit within this. It is bonded into place and takes a while to cure completely. Then the steel insert is threaded n chased to turn threads into this new steel insert. Reassemble the bottom bracket bearings, shaft and cups. Tightened into place. Ridden for a few hours then re-tightened. Ridden for a week then retightened. Yep it's not an easy job, it takes time. But done right and with the right tools and approach is 100% effective. Even better strength and rigidity than the original fit. Costly, yes $350 - $400 to complete. Do i love this frame.. Yes. Why. I don't know. I just like keeping things that have aged with me. Other than this old damaged bottom bracket thread fault this bike rides unbelievably well. I'd rather fix something than throw it aways. I've got an eye on a second hand frame if things don't go well. It's my old ride, my new bike has been kicking my ass!!