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PostPosted: Wed Jun 26, 2013 5:58 pm 
Dirt Disciple

Joined: Mon Jan 21, 2013 3:41 pm
Posts: 55
Location: Bromley
What happened:
I went to my lbs ask asked them to remove the bottom bracket from my Mercian and to put it in my Raleigh Royal. I had presumed both were a regular 68mm British bottom bracket.

What they said:
After they removed the bb they said the Mercian was in fact a 66mm bb not a 68mm bb and therefore the bottom bracket they took out wouldn't fit in the Raleigh.

Fine.

However when I got home I had a look at the bottom bracket they took out, and it says R - 68.
Which suggests to me it's a 68mm bottom bracket.
As such such would suggest it would fit in the Raleigh, and the Mercian is in fact a 68mm.



Are they wrong? Or am I missing something.
Normally I'm wrong and the lbs are right but it seems strange to me.

Picture of the bb in question are below.
Any ideas?


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PostPosted: Wed Jun 26, 2013 6:29 pm 
retrobike rider
retrobike rider
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Joined: Tue Jan 29, 2008 11:04 pm
Posts: 1802
Location: A wretched hive of scum and villainy...
I suspect that you're right...

It's possible (but but unlikely) that the Mercian BB shell had been faced short to 66mm. Measure end-to-end across the faces of the BB shell. But that's no reason why the BB wouldn't fit in the Raleigh. That's the beauty of cup and cone BB axles...loads of adjustability/tolerance.

If anything, it would be the Raleigh that was non-standard, not the Mercian, but here it looks like standard BSA threads all round, nothing weird.

If the Mercian BB shell is a little short, giving some chainline trouble, or unequal crank/pedal spacing to the frame, the drive side fixed cup can be moved out a little with a 1 or 2mm spacer, no probs.

All the best,


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PostPosted: Wed Jun 26, 2013 6:43 pm 
Dirt Disciple

Joined: Mon Jan 21, 2013 3:41 pm
Posts: 55
Location: Bromley
Interesting interesting,

You are right, a quick measure shows its 66mm and they in fact gave me 2 1mm spacers in order to fit a 68mm bottom bracket in the future to the Mercian. Perfect.

The Raleigh is defintely a standard 68mm with the same threads. Would have any changes been made to the bottom bracket in the Mercian to make it work with 66mm? I'm trying to work out why they thought it wouldn't work.

It definitely screws in etc as I've just checked to make sure.

Thanks for the reply


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PostPosted: Wed Jun 26, 2013 7:50 pm 
retrobike rider
retrobike rider
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Joined: Tue Jan 29, 2008 11:04 pm
Posts: 1802
Location: A wretched hive of scum and villainy...
Good...looks like they're on the ball.

You may not actually need the spacers. It all depends on whether the missing 2mm of the Mercian BB shell has been taken off one side, or both equally.
I'd assemble the BB as normal (just finger tight will do in this case) but fit the cranks parallel, rather than opposed, and fully tight on the axle. Compare the spacing between the inside faces of the cranks at the pedals, and the chainstays. That way, you can see better if the BB axle needs to be shuffled to the right, using the spacers the LBS has supplied, fitted behind the fixed cup.

You might also want to use the spacers if, even when the cranks are properly spaced, the non-drive adjustable cup sticks out of the lockring when assembled. Doesn't matter mechanically, but looks unsightly.

Once it's all looking nice and even, remove the cranks and refit the whole lot properly tight.

All the best,


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PostPosted: Thu Jun 27, 2013 8:22 am 
r.B.o.T.M. & P.o.T.M. Winner
r.B.o.T.M. & P.o.T.M. Winner
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Joined: Thu Nov 22, 2007 10:51 am
Posts: 2215
Location: Camel Land
BB30, BB86, PF90 anyone :lol: :lol:


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PostPosted: Thu Jun 27, 2013 12:58 pm 
retrobike rider
retrobike rider
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Joined: Tue Jan 29, 2008 11:04 pm
Posts: 1802
Location: A wretched hive of scum and villainy...
Quote:
BB30, BB86, PF90 anyone
True..
Combine that with all the ahead, integrated, semi-integrated, 1.5" tapered, 45-36º etc in headsets and we have a component/frame obsolescence timebomb :shock:

All the best,


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PostPosted: Thu Jun 27, 2013 10:56 pm 
Retrobike Sponsor
Retrobike Sponsor
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Joined: Sat May 22, 2010 10:33 pm
Posts: 2192
Location: Suffolk
That why I like threaded headset and at best 1 1/8" external cup headset and proper threaded BB's for my personal bikes. to be fair the 1 1/8 th intergrated standard is so well established that bearings will be around for a long while and BB30 just uses 6806 bearings which are a standard size used in many applications so no obsleance there. Still too many standards but is not the way it has always been. Just look at all the tyre standards over the years.


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