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Main
Date: 10 Aug 2007 01:16:35
From: ron
Subject: Tandem question
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Captain bottom bracket in an eccentric shell. Shell can go in either way.
Should left-threaded threads be on the right side or the left side? My
guess is it should be on the left because that's where the chainwheel is
and because you want the longer side of the spindle to attached to the
crank with the chainwheel. Am I right?
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Date: 10 Aug 2007 11:36:30
From: Clive George
Subject: Re: Tandem question
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"ron" <ranyc2thousand@yahoo.com > wrote in message
news:46bbbc73$0$29703$4c368faf@roadrunner.com...
> Captain bottom bracket in an eccentric shell. Shell can go in either way.
> Should left-threaded threads be on the right side or the left side? My
> guess is it should be on the left because that's where the chainwheel is
> and because you want the longer side of the spindle to attached to the
> crank with the chainwheel. Am I right?
No - BB should be set up as it is on a single bike. ie LH thread on the
right. (Pedals, LH on left, BB, LH on right).
http://www.sheldonbrown.com/gloss_bo-z.html#bottom
The spindle should be symmetrical, ie the bit sticking out beyond the frame
should be the same length. On eg 73mm shimano BBs (well, at least some), the
body of BB is the same length as on the 68mm ones. The extra comes from the
spacer/cup, and the spindle is 5mm longer on that side.
(On our tandem I actually use that to get the two different brands of
chainwheel to work - the LH needs a longer axle than the RH, so I use a 73mm
BB with a 68mm spacer/cup.)
If your chainset requires an asymmetric spindle, all bets are off - do
whatever you need to to make it work. But if you put the shell on backwards,
might be worth taking steps to cope with it potentially undoing -
inspection, loctite, whatever.
cheers,
clive
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Date: 09 Aug 2007 23:05:25
From: Mark
Subject: Re: Tandem question
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ron wrote:
> Captain bottom bracket in an eccentric shell. Shell can go in either way.
> Should left-threaded threads be on the right side or the left side? My
> guess is it should be on the left because that's where the chainwheel is
> and because you want the longer side of the spindle to attached to the
> crank with the chainwheel. Am I right?
You want the threads set up the same as on a single bike, regardless of
which side the chainwheel is on. The spindle turns in the same
direction, so the cups will self-loosen or self-tighten in the same
manner depending on which way the threads are oriented. Assuming it's
an English thread, that's left-hand thread on the right.
The longer side of the spindle is a separate matter; the spindle can be
oriented either way in the cups, whatever spaces the crankarms correctly
is the way you want it.
Oh, I see - if you have a cartridge BB, you may have issues here - if
the threaded "cups" don't separate from the cartridge.
Mark J.
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Date: 09 Aug 2007 19:13:52
From: SMS
Subject: Re: Tandem question
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ron wrote:
> Captain bottom bracket in an eccentric shell. Shell can go in either way.
> Should left-threaded threads be on the right side or the left side? My
> guess is it should be on the left because that's where the chainwheel is
> and because you want the longer side of the spindle to attached to the
> crank with the chainwheel. Am I right?
I'm sure it's as you say. I have a tandem with the same sort of bottom
bracket, and left hand threads are on the left.
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