A left-handed thread

[bertgrower]

I am looking for the following:
Bolt m12 x 100 mm and nut to fit
A left-handed thread
Where i can obtain them?
Purpose to remove adjustable cup on bottom bracket.

[Brucey]

a decent fastener suppliers might have the things you want. Searching on Ebay may reveal what you want too.

However I have a cheapskate suggestion for you; nip down the scrappies and snaffle some track rods off a decent size car or van. Very many use M14 or M12 threaded rod ends with left and right handed threads on them in matched pairs. With a little ingenuity these could be made into a suitable tool.

Needless to say car spare shops and motorsport parts suppliers sell LH threaded nuts to fit common track rod threadings (and this is why many fastener suppliers sell LH nuts, but not LH threaded bolts....). It is worth noting that these threads are usually finer pitch than standard metric threads (at any given diameter) and therefore provide a better self-locking action. Even so this method is not 100% reliable; BB cups can always find a way to slip if they really want to.

If you just want the cup out, there are a few methods that are worth considering as alternatives

1) weld something onto the cup
2) use the 'hammer massage' approach.

The 'hammer massage' comprises holding a heavy (1.5 to 2lb) hammer against one side of the BB shell (as a bolster) and then giving it a smart whack or two on the other side with a 1lb hammer, i.e. 180 degrees away from where the bolster is, so that the BB shell and cup are squeezed ). Then move about 90 degrees or so round the cup and repeat. This will make marks on the BB shell but it does encourage seized cups to relinquish their hold in the BB shell in short order.

cheers

[bertgrower]

I let you know how I get on.

I have no finance interest in the company below.

Left Handed Thread

I obtained stainless Streel rod
100 and 150 mm lengths plus nuts
Total cost about £15?
GWR Fasteners Limited
Unit 1 Weston Farm, Weston Lane, Oswestry, Shropshire, SY10 9ES
Tel: 01691 654979

General Enquiries Email:
jude@gwr-fasteners.co.uk
Manufacturing Enquiries Email:
sales@gwr-fasteners.co.uK
GWR Colourfast Enquiries Email:
jude@gwr-fasteners.co.uk
http://www.gwr-fasteners.co.uk/metric-l ... -287-c.asp

[colin54]

Will a normal right hand thread bolt not work as per Sheldon Brown's method here ( bottom of page ) ?

https://www.sheldonbrown.com/tooltips/bbcups.html

[bertgrower]

Will a normal right hand thread bolt not work as per Sheldon Brown's method here ( bottom of page ) ?

https://www.sheldonbrown.com/tooltips/bbcups.html

No the drive side is a left hand thread.

[colin54]

Will a normal right hand thread bolt not work as per Sheldon Brown's method here ( bottom of page ) ?

https://www.sheldonbrown.com/tooltips/bbcups.html

No the drive side is a left hand thread.

Hi Bert ,yes I realise that . On the fixed side cup he is tightening the bolt to the nut and on the drive-side cup with the left hand

thread he is holding the bolt and tightening the nut. undoing both cups towards the front of the bike in each case .That's how I read

the last paragraphs anyway ( nut on outside in both cases ), worth a try maybe if you haven't already?

[drossall]

Or put on two nuts, one as a lock nut.

[Brucey]

the whole idea is that if the bolt thread is the opposite thread from the cup, the arrangement ought to be self-tightening when the cups are being undone.

In all fairness getting the initial movement is more than half the battle, so there is no reason why a RH threaded bolt can't be used on the NDS cup to get the initial movement , and then unscrewed some other way (at lower torque, hopefully)

cheers

[Mick F]

To get the LH cup out, fit a normal suitably sized nut and bolt through the BB shell and tighten it.
Then, using an extension, fit a socket to the nut on the inside of the cup passing through the BB shell, and turn it clockwise as you look through.
This turns - or attempts to turn - the LH cup anti-clockwise viewed from the outside, to undo it.

[Brucey]

that is a good point; the directions are correct, however the friction coefficients might not be. I think the whole scheme only works (when it works) if the nut binds against the cup but the bolt is still able to turn thus tightening everything. I would suppose that most usually the bearing surface is worn and unplated, and thus the nut can bite into it, but the bolt head is able to slip over the smooth, chrome plated external surface. If the bolt is put through from the inside instead, the nut may slip easily on the outside surface of the cup and the self-tightening effect may not be as good as normal. It would certainly be worth a go though.

cheers

[drossall]

I still think that a locknut tightened to a greater torque than that needed to undo the cup should allow the latter to be shifted.

[Mick F]

Yep.

I reckon that if your really really REALLY tighten the nut and bolt, it will grip enough to undo the cup.