Bottom Bracket adjustment on tour

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mjr
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Bottom Bracket adjustment on tour

Postby mjr » 13 May 2019, 6:43pm

I fear I've asked this before but I can't find it: is there a way to tighten up a UN-55-type cartridge bottom bracket cup without removing the cranks while on tour?

Longer version: I've had a crash (someone hitting my bike while I wasn't on it!) knock the non-drive-side cup loose before, but it was the day I returned home so I just rode it gingerly, then removed the crank once at home and tightened it up with a socket, but I do wonder what I'd do if I wasn't about to return home. Find a shop or bike co-op I guess, but that could be some distance away. Is there any way I could make a roadside repair without breaking splines or similar?

It almost makes me wish to convert more bikes to loose BBs, nut-faced adjustable cups and lock rings... but only almost ;)
MJR, mostly pedalling 3-speed roadsters. KL+West Norfolk BUG incl social easy rides http://www.klwnbug.co.uk
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iandriver
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Re: Bottom Bracket adjustment on tour

Postby iandriver » 13 May 2019, 6:56pm

Personally I'd have used something on my multi tool as a drift and tapped it gently. A non drive side cup not being that tight shouldn't be too much of a problem, I wouldn't have thought.
Supporter of the A10 corridor cycling campaign serving Royston to Cambridge http://a10corridorcycle.com. Never knew gardening secateurs were an essential part of the on bike tool kit until I took up campaigning.....

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mjr
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Re: Bottom Bracket adjustment on tour

Postby mjr » 13 May 2019, 7:04pm

iandriver wrote:Personally I'd have used something on my multi tool as a drift and tapped it gently. A non drive side cup not being that tight shouldn't be too much of a problem, I wouldn't have thought.

I was worried that using a screwdriver as a drift might damage splines and render it unrepairable. The cranks were wobbling visibly, but not enough to hit the chainguard.
MJR, mostly pedalling 3-speed roadsters. KL+West Norfolk BUG incl social easy rides http://www.klwnbug.co.uk
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Brucey
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Re: Bottom Bracket adjustment on tour

Postby Brucey » 13 May 2019, 7:57pm

I'm struggling to see how a prang might loosen the BB mountings as you describe. Are you sure that you didn't just notice that the thing was loose when you examined the bike more carefully than usual?

Also FWIW current BB55 units often have a poorly toleranced LH cup so that they are more likely to work loose than normal. If the fit of the LH cup is corrected (eg by throwing it away and using something different instead, that fits properly) then the BB oughtn't come loose.

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mjr
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Re: Bottom Bracket adjustment on tour

Postby mjr » 14 May 2019, 4:26pm

Brucey wrote:I'm struggling to see how a prang might loosen the BB mountings as you describe. Are you sure that you didn't just notice that the thing was loose when you examined the bike more carefully than usual?

It's possible, but I suspect what happened was that the force applied to the RH side was enough to hammer the LH cup out by jumping a turn of the threads. Could that be more likely because of the poor tolerance problem you describe?

Anyway, it's now worked loose again so I think I'm going to take the LH cup right out, check both cup and shell threads for damage and if the shell threads look OK, I'll see if I can find another cartridge LH cup in the shed (or ask an LBS if they have a spare, or just buy a whole new BB :roll: ) that I can try instead. If the shell's damaged, I'll swear. I thought I'd gotten away lightly with no visible damage - maybe it was all tyre into RH crank.
MJR, mostly pedalling 3-speed roadsters. KL+West Norfolk BUG incl social easy rides http://www.klwnbug.co.uk
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531colin
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Re: Bottom Bracket adjustment on tour

Postby 531colin » 14 May 2019, 7:00pm

mjr wrote:.........I suspect what happened was that the force applied to the RH side was enough to hammer the LH cup out by jumping a turn of the threads...........

But the RH side flange prevents the unit from moving within the BB shell.

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Re: Bottom Bracket adjustment on tour

Postby Brucey » 14 May 2019, 9:20pm

the nature of the crappy fit between the LH cup and the BB unit means that the slightest axial movement of the parts (eg via settling) can cause the BB not to be supported against radial loads on the LHS, i.e. it is bound to work loose.

I have wondered if shimano's intention is to cement the square taper BB's position (in their largely imagined hierarchy of quality) at the bottom of the heap by turning a basically good design into an unreliable one by making it very badly. The LH cups on current UN55 BBs fit so badly that I won't use them.

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mjr
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Re: Bottom Bracket adjustment on tour

Postby mjr » 14 May 2019, 9:48pm

That's disappointing. Any suggestions for the current best square taper cartridges?

531colin wrote:But the RH side flange prevents the unit from moving within the BB shell.

Maybe the RH is damaged too? I'll check when I take it out.
MJR, mostly pedalling 3-speed roadsters. KL+West Norfolk BUG incl social easy rides http://www.klwnbug.co.uk
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531colin
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Re: Bottom Bracket adjustment on tour

Postby 531colin » 15 May 2019, 8:42pm

Brucey wrote:….... The LH cups on current UN55 BBs fit so badly that I won't use them...........

Thats a nuisance. I have to replace an old Stronglight unit thats gone rumbly, I was going to use Shimano because they were reckoned to be better units than the Stronglight. Perhaps I should just drill it and bung some SFG in.

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Re: Bottom Bracket adjustment on tour

Postby Brucey » 15 May 2019, 8:58pm

the bearings seem OK but the LH cups I have seen are a bad fit. If you have a cup from an old shimano BB the chances are that it will fit OK. So do some others. It is also possible to install the BB unit with shims and/or epoxy resin between the LH cup and the centre unit.

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