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PostPosted: Sat Sep 15, 2012 3:05 pm 
Dirt Disciple
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Joined: Thu Aug 11, 2011 2:46 pm
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Location: Watford
Hi all

I have a rebuilt 3-speed with a 127mm (Shim. UN54) b/bracket as per the recommendations for the replacement crankset (it came to me with caged bearings and loose cottered cranks)

Its slightly out of chainline, as the bike has a chaincase that's held by being sandwiched between the B/B driveside shell and the frame - this wasnt an issue at first but after a year the chain's got enough lateral wear that it vibrates loudly when I put some effort on as the whole assembly is 1mm or 2mm to the right of where it should be due to the extra thickness.

Does anyone know if you can get a 125mm or 126mm sealed-cartridge bottom bracket for 68mm shells and standard threading? I found some for 73mm shells but have only seen a YST threadless BB (which general reviews warn me off buying) for 68mm

Cheers


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PostPosted: Sat Sep 15, 2012 4:27 pm 
Road Moderator
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can you slightly modify the chainguard? or perhaps buy a new chain?


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PostPosted: Sat Sep 15, 2012 4:31 pm 
Dirt Disciple
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Oh certainly I could just remove the chainguard or make some sort of hanger bracket for it off the seatpost and remove the BB-mounted bracket.

Chain replacement is even easier but in the end wasteful. The ideal solution should be to ensure a good chainline.

I'd just like to find a workaround that leaves this bicycle as authentic as can be.


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PostPosted: Sat Sep 15, 2012 4:34 pm 
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With some chainguards you can bend the original bracket enough to allow clearance. Why would you mount it from the seatpost? That would just look stupid :wink:

But yes perfect chainline would be best.


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PostPosted: Sat Sep 15, 2012 4:37 pm 
Dirt Disciple
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Location: Watford
possibly you misunderstand

The chainguard hangs from a bracket with a hole in it. The bottom bracket goes through that hole, sandwiching the chainguard mount between itself and the bicycle BB shell

No amount of bending will make it any thinner therefore either the chainwheel will be too far out by the width of the chainguard supporting bracket... or i must shorten the axle /find a different chainwheel / something else


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PostPosted: Sat Sep 15, 2012 4:40 pm 
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sorry yes re-read the op and I see now. think i should be asleep rather than posting useless advice on here :roll:


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PostPosted: Sat Sep 15, 2012 8:58 pm 
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Joined: Tue Jun 14, 2011 10:51 am
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could you use a 122.5 and then use bottom bracket spacers to move it out to the right place?

http://www.sjscycles.co.uk/wheels-manuf ... prod17701/

they have a 2mm one, not sure if you can use a combination of different sizes I can't see why not. Obviously this would offset your cranks to one side though, so check the left one wont clash the chain stay or anything ( i fitted one to my other halfs Wisp to stop the chain rings scraping the right stay, the left then clashed with the kick stand bracket to that had to be removed).


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PostPosted: Sun Sep 16, 2012 12:37 pm 
Dirt Disciple
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interesting... I'll look into that

Only obvious concern is I'd be restricting the degree to which the drive-side threads of the B/Bracket screwed into the B/B shell on the frame by at least 3mm...

I know that on a standard B/B the pedalling tightens rather than loosens, but is this likely to be a problem?


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PostPosted: Sun Sep 16, 2012 1:53 pm 
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It's just my personal preference, I'm not implying that the other suggestions won't work, but I like to keep things as simple as possible.

So if I was presented with this problem, and being unable to source a wider BB, I'd remount the chainguard hanger.

True, it will no longer be as it left the shop, but the adaptation will be part of the bike's history and barely noticeable anyway.


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PostPosted: Sun Sep 16, 2012 4:59 pm 
Dirt Disciple
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Thanks

I had hoped that someone would point out an obscure supplier of high quality sealed B/Bs with nonstandard axle lengths. I think in the absence of that you certainly have the right solution....


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