Bottom Brackets - full on expert needed!

[development_cycle]

Ok so here is the score, I have a frame that has unfortunately seen better days in the BB thread department. I have had them gone through by my lbs but they tell me they are beyond repair, so the question is what can I do?

Before the barrage of replies suggesting either a Mavic/Stonglight/YST or other threadless bb, I did look into these and found references only to bb's made for 68mm shells where-as mine has a 73mm shell.

So I need ideas, and not temporary ones but what do I do with this frame ideas.

For example, would it be an absolute no-no to have an engineering shop simply take 2.5mm from each side of the shell making it 68mm and go get a threadless bb? Are there modern bb's like the external bearing ones (don't do modern so no idea what they are called) that don't need threads?

Your thoughts are most welcome, well sensible ones anyway!

 

[one-eyed_jim]

What's the frame made of? What cranks are you hoping to use?

 

[development_cycle]

good questions oej, so the frame is steel, prestige I think, and as for cranks, to be honest I have no idea, old, new, whatever were possible depending on what mod's might need to be made to the frame.

 

[Charlieboy28]

here you go, seems the sleeve it then cut a thread into the sleeve

http://www.mountainbikecomponents.co.uk/repair.asp

 

[MikeD]

Get the whole shell replaced? Or, and I haven't thought about this at all so there'll be a good reason it won't work, get suitably-sized bits of tube brazed on to the ends of the existing BB to take a Press-Fit BB. You need 92mm overall width and, er, some internal diameter that I can't remember. 41mm maybe. Don't know if there'd be room enough for sufficient insertion depth for the bearings, though, you're not going to get more than 10mm of new tube each side.

 

[development_cycle]

here you go, seems the sleeve it then cut a thread into the sleeve

http://www.mountainbikecomponents.co.uk/repair.asp

Wow, a helicoil, I had never even considered that someone would do that for a bb shell. Looks like that's the.....oh hold on £55 per side (plus postage both ways), hmm, ok well it is an option, thanks.

 

[Charlieboy28]

Araldite it :shock: :shock:

 

[development_cycle]

Get the whole shell replaced? Or, and I haven't thought about this at all so there'll be a good reason it won't work, get suitably-sized bits of tube brazed on to the ends of the existing BB to take a Press-Fit BB. You need 92mm overall width and, er, some internal diameter that I can't remember. 41mm maybe. Don't know if there'd be room enough for sufficient insertion depth for the bearings, though, you're not going to get more than 10mm of new tube each side.

Ok Mike you've lost me, so this is some sort of modern thing I assume, and could work with a new tube of the right diameter etc inserted, or are you saying that I would need to have the BB shell replaced? To be honest at £55 per side to get a helicoil inserted by a frame builders surely the cost of just getting a new bb sheel welded in wouldn't be mnuch different?

Keep them coming folks (and Mike please try again with that explanation as it went in and then out again) :shock:

 

[development_cycle]

Araldite it :shock: :shock:

Ok, yep, had wondered if there might be some mileage in that, older style seperate cones type BB required I assume though, not sealed cartridge shimano jobby?

 

[MikeD]

That was two separate options

In theory a framebuilder could replace the whole shell.

Or you could go crazy and attempt to retrofit a new threadless BB standard by extending the existing shell in an excitingly untested way with little chance of success

Or helicoil it.

I'd phone a framebuilder and see what they say. THere's not going to be a cheap option (apart from the Araldite).

How chewed is it? There might be a grade of Loctite that'll hold but give you a vague chance of removal one day.

Or cut the front end off and make a stool.