Bottom bracket shell thread repair

Keep_Her_Lit

The threads in the BB shell of my commuting MTB gave up the ghost a few years ago (root cause: a seized BB which needed a very unhealthy amount of force to remove).

Since then, I've been using this handy internally threaded YST BB:



It's cheap and cheerful and works just fine.

The downside is that it's square taper and half decent square taper MTB chainsets are getting hard to find.

Since I'd like to wring a few more years out of the frame if possible, it would be good to restore the threads to allow the use of 21st century chainsets. These folks in Eastside Bikes, Edinburgh (scroll to bottom) will tap the shell out to a larger thread and insert a helicoil to bring it back to 1.37" x 24 TPI. £50 seems OK for a job I'm never going to be able to do myself.

Question: does anybody know of a shop offering this service on this side of the water? Better still, if you've had the job done, how much did it cost and were you satisfied with it?

Any info would be appreciated. Thanks.

morana

I remeber a lad in my old club had a similar issue. He cut a line in the shell with a hacksaw, clamped and welded it and then rethreaded and it was fine. I am sure cliff in Eurocycles sth william st could do something for you..

Keep_Her_Lit

Thanks, that's quite a neat solution! I see that I can get my hands on the right & left hand taps for a mere £500:

http://www.parker-international.co.uk/7252/Park-Tool-BTS1-Bottom-Bracket-Tapping---Facing-Set.html

[Has anyone else noticed that everything on Parker International is sold for "Only" £XXX?]

Better have a word with your man Cliff then ...

pprendeville

You could try contacting an engineering firm to see if they would be able to help. One such firm I used to deal with when I was employed (seems like a long time ago) are JF Dunne Engineering. You'd probably be talking a few hundred quid though unless you can get the helicoils yourself individually as they're an uncommon size and therefore pricy. Try radionics or farnell for them.

Keep_Her_Lit

Thanks PP. A quick sniff around hasn’t uncovered those helicoils. As for the oversized, left hand threaded tap, you’re probably looking at re-mortgaging the house! I’d be amazed if a general engineering shop already had such a tool in stock – unless it has a common application elsewhere in industry – but I think 1.37” x 24 TPI is cycling specific.

Nevertheless, I’ll follow up on your recommendation and give JF Dunne Engineering a call. I may come away with some new ideas on how to approach the problem. I’ll tell them that Mr. (I assume) Prendeville sent me.

As an alternative, I see that some people have got the inside of the shell built up with weld so that the original thread size can be re-tapped.

pprendeville

Keep_Her_Lit wrote: »

Thanks PP. A quick sniff around hasn’t uncovered those helicoils. As for the oversized, left hand threaded tap, you’re probably looking at re-mortgaging the house! I’d be amazed if a general engineering shop already had such a tool in stock – unless it has a common application elsewhere in industry – but I think 1.37” x 24 TPI is cycling specific.

Nevertheless, I’ll follow up on your recommendation and give JF Dunne Engineering a call. I may come away with some new ideas on how to approach the problem. I’ll tell them that Mr. (I assume) Prendeville sent me.

As an alternative, I see that some people have got the inside of the shell built up with weld so that the original thread size can be re-tapped.

Ya unusual sized taps cost a fortune. Little demand = high price in the engineering world or any world for that matter. I did use 1/2" helicoils before and the tap was a fair monster so I'd say the ones you're looking for must be massive.

Ya, tell them I recommended you. Use to work up the road from them with Allied Automation. Good crowd.

Ya, I saw the post about the weld. You'd just want to make sure it's a decent weld. Lots of dodgy self taught people out there.

Holyboy

Hi all,

Okie dokie, lets start at the beginning, is your frame steel or aluminium?
If it's steel there are a few more options, but firstly before going down these roads I have to ask why? It is still possible to get a good quality square taper chainset with removable rings, so I'm not sure why you need to start messing with the frame, the thread-less B.B.s are not the best but they do serve a purpose, any way if it's steel the old "cut and shut" that's the cutting, shutting, welding and tapping is an option but one I'm not too found of as the temperature required for welding is usually more than the tubes of the frame are designed to withstand so you end up with an annealed(soft) B.B. shell.
Another option is to ream out and silver solder a piece of tube into the shell and then re-thread it, unfortunately I don't have an oxy set up(yet, I'm learning the basics of frame building before I invest in one),but if you're still hell bent on repairing the frame whether steel or alloy, then it can be reamed and then re-threaded to Italian sized thread but then thinking about it, it might not give you many more options than square taper!
Finally, are you really sure the threads are completely gone??
Hope I've been of some help,

Dara,

<snip>

Keep_Her_Lit

Holyboy wrote: »

is your frame steel or aluminium?

It’s 7005 aluminium (Scott Vail, 1998).

If it's steel there are a few more options, but firstly before going down these roads I have to ask why? It is still possible to get a good quality square taper chainset with removable rings, so I'm not sure why you need to start messing with the frame, the thread-less B.B.s are not the best but they do serve a purpose

I’m looking for a 48-36-26 (or 48-38-28) chainset with 175mm cranks. I don’t want to go with 44T or 42T, since I only use the bike on the road with slicks. Taking Shimano as an example, only their Alivio chainset now meets those requirements in square taper. Square taper has disappeared as an option from all the higher groupsets.

Yes, I’m sure that the Alivio chainset would do the job and I generally look for value for money when replacing parts. That said, I tend to avoid low end components, as in many cases they’re heavier, don’t work as well, don’t last as long and have poorer finish than mid-range components.

A similar trend is evident among other component manufacturers (e.g. Truvativ, FSA, Origin-8), with fewer square taper options available than in previous years. For now, a couple of possible options are…

http://www.origin-8.com/?page_id=91&short_code=Origin8+Trekking+Crankset&cl1=CRANK+ARMS+%26+SETS

… or this 50-34T road compact …

http://www.fullspeedahead.com/products/37/Vero-Compact

The thing is, if the BB shell in my frame can be reconditioned at a reasonable cost and without any complications, then I can still use either of the above but also a whole lot more besides. I suppose my concern is that without a repair, the choice may well be even more limited in another year or so and I’ll end up with nothing but nasty BSO parts to choose from. Either that or having to trawl e-bay for something second hand.

any way if it's steel the old "cut and shut" that's the cutting, shutting, welding and tapping is an option but one I'm not too found of as the temperature required for welding is usually more than the tubes of the frame are designed to withstand so you end up with an annealed(soft) B.B. shell.
Another option is to ream out and silver solder a piece of tube into the shell and then re-thread it, unfortunately I don't have an oxy set up(yet, I'm learning the basics of frame building before I invest in one),but if you're still hell bent on repairing the frame whether steel or alloy, then it can be reamed and then re-threaded to Italian sized thread but then thinking about it, it might not give you many more options than square taper!

Well, I wouldn’t say that I’m "hell bent" on repairing the frame. "Seriously considering it" would probably be closer to the mark. The service offered by Eastside Bikes ticked the boxes for me (see the link in my OP). They’ll restore the thread to its original size, without using heat, for a reasonable charge.

Finally, are you really sure the threads are completely gone?

Only about one third of the threads remained intact after the initial trauma. I still managed to use conventional BB’s for a couple more years after that. But then the chain started rubbing pretty badly against the front derailleur cage one morning on the way to work. That was because the BB had wandered sideways out of the frame by a few mm. I spent the return journey stopping periodically to shove it back into the frame. So yes, the threads are well and truly gone.

Hope I've been of some help,

Yes, you have thanks. The more ideas I get, the more likely I am to make a good decision in the end.

kona

Why bother spending time and effort fluting around with a 13 year old aluminium frame? You could just pick up a frame for a few quid?...

Any Bike shop will have those Taps for the BB threads, Id try retap them and see where that gets you. As has been said, it can be fixed with a Insert then tap the insert out, but it really isnt worth the effort and money.

Holyboy

Ah I used to have a Scott Vail, think I bought it in '98 too, sold it when I moved to London, it was a nice little bike though, but above may be right it might be time to to let go, steel is the way forward, so much more possibilities, but I think I have a Deore LX square taper chainset lying around, I could fit some larger rings to it for you if you want.