Bottom Bracket Threads Failed - Best Solution?

[howfar]

Twenty five miles from home and the UN54 goes looser and looser at both ends! The units been in for years and the frame is about 26 years old and when dismantled the drive side was the problem - it would tighten up to a point then slip. Tried another UN54 and same issue so the frame thread on the drive side is the issue. Must have been fretting for some time.

I'll get the frame re-tapped but expect I'll need something extra - any advice on the best method would be appreciated. Is PTFE wound around the units thread a good idea or should I glue with Lotite epoxy and hope the unit lasts long enough to warrant heating the frame up to 150c when the time comes to replace?

Ian

[NATURAL ANKLING]

Hi,
Plastic padding chemical metal is the best if the threads are now stripped or close to stripping.

http://www.ebay.co.uk/itm/PLASTIC-PADDI ... xyFjNSQhy9
You need to degrease thoroughly

There are Loctite stuff that fills gaps but not sure it will take up all the slop if there has been much movement.
This stuff is resistant to grease and petrol etc.
I have been using it for over 35 years it works.

May be too good if you want to remove later?

[gaz]

Threadless BB? https://www.edinburghbicycle.com/yst-th ... acket.html

[pete75]

It costs about 45 quid for a proper bottom bracket repair at a frame builder like Vernon Barker. http://www.vernonbarkercycles.co.uk/prices_frames.html

[andrew_s]

When my BB threads went similarly, I sent the frame to Argos in Bristol, who reamed out the old threads, brazed in a sleeve, and cut new threads in the sleeve. It's been OK for the 15 years since. Frame respray required.

[Redvee]

When my BB threads went similarly, I sent the frame to Argos in Bristol, who reamed out the old threads, brazed in a sleeve, and cut new threads in the sleeve. It's been OK for the 15 years since. Frame respray required.

I had a KO'd BB repaired by Argos. They reamed and sleeved it with no need for a respray.

[Paul Smith SRCC]

If you can get the correct width and taper the threadless BB unit that 'gaz' referenced would work.

If it's steel a frame builder can cut and shut the BB Shell, they simply cut a slot each side, press the cut shut, retap the threads; job done. They will do this on the under side of the BB shell, so paint damage will be both minimal and in reality out of sight

[howfar]

Thanks for all the pointers everyone - after tapping out I'll see how the unit tightens up. Looks like a thread less unit would be the route of least resistance.

Anyone used Loctite Form a Thread before? It looks like a possible easy solution but sounds too good to be true....

Ian

[Brucey]

threadless units can be troublesome in some cases, and the actual bearings can be of indifferent quality too.

If it were my bike I'd probably use epoxy resin on a standard BB unit. If you use one where there are two separate cups (e.g. sun race, or chin huar, or token) then should the unit fail, you can renew all the parts except the bonded cup provided only the one cup is bonded into the frame.

Another repair method I have applied is to use MIG welding to add material to the inside of the BB shell in a few places. This is dressed back (e.g. by grinding, so that the measured diameter is comparable to the root diameter of the BB threading) and then a BB tap can be run through to make the thread good. This need not require a lot of welding or paint damage; what is required is usually on the lower half of the BB shell in a place where paint damage isn't easily seen. If the RH BB cup is steel, no more than a few small blobs of weld metal is all that is required.

Obviously both the above techniques keep your options open for any later repairs.

cheers

[howfar]

Thanks Brucey

If the thread less units are variable I'll stick to the Shimano UN5x series as they seem to last forever. I don't have the funds for a proper job like sleeving or cut n' shutting and courier costs and don't have access to MIG equipment so am looking at epoxy but am tempted by Loctite Form A Thread as I won't have to heat the frame for removal. Are any of the double cup BB units mentioned at least 50% as good as Shimano?

Ian

[Brucey]

I don't know how well the Loctite product works so I can't comment on that. Nor much on threadless units tbh, except to note that they seem to fail or work loose more than standard types such as the shimano ones.

IIRC the current UN5x models have an integrated steel cup on the RHS. I think that if you fit one of those with epoxy resin, it'll work fine (it always has done for me....).

When removal time comes, the epoxy will be a little degraded anyway. A little heat (not enough to hurt the paint) and high torque ought to shift it. I think (using various horrible tools to remove a seized unit) I have put over 500ftlbs through a bottom bracket tool before now, which ought to shift almost any BB really.

cheers

[bikepacker]

I have had an Acor threadless bottom bracket on my old Galaxy frame now for about 6 years with no problem. The only trouble I did get was after an overall I tried a more expensive bottom bracket. It did not work out as expected and I replaced it with the Acor and it has been okay. Since the replacement I have done a good few miles including a cycle camping trip in Wales