Tandem eccentric bottom bracket conundrum

General bike chat that does not fit elsewhere
bonk man
Posts: 1021
Joined: Sat Mar 20, 2004 22:41 pm

Tandem eccentric bottom bracket conundrum

Postby bonk man » Tue Jun 17, 2008 18:07 pm

I have just acquired a tandem, [apparently a Swallow] with no b/b eccentric. I have one from a Gitane but it is the wrong size, could anyone tell me the correct size.

The dimensions are .. shell width 50mm and closed diameter of the shell is about 53mm. I obviously don't want to shell out [ :? ] for the wrong one.... :roll:

cheers.........................

fatbee
Posts: 558
Joined: Thu Apr 08, 2004 12:09 pm

Postby fatbee » Sun Jun 22, 2008 12:11 pm

I was in your position many years ago, and came up with two budget solutions :

1) Source or fabricate two chunky discs (aluminium probably best) that are the tiniest, tiniest bit larger in diameter than the BB shell when closed. Drill a normal-BB-sized hole identically eccentrically in each, and then epxoy a cheap cartridge unit (I used a plastic FAG jobbie,) into the discs so that their outer faces are the same distance apart as the BB shell's width.

2) Build or adapt a chain doofer (like the ones downhillers and singlespeeders use) and mount it on the "drainpipe" tube that conects the tandem's front and rear BB shells, then adjust it so's it just takes up any slack in the timing chain.

The second idea is easier but looks more Heath-Robinson, but they both work.

Good luck!!

Steve928
Posts: 314
Joined: Sat Jun 07, 2003 16:35 pm

Postby Steve928 » Sun Jun 22, 2008 12:38 pm

I have a s/h eccentric here that should fit - we just scrapped our old Pashley tandem frame.

It's 53mm diameter (using my plastic calipers..) and the clamping area is from 26 to 60mm across i.e. about 5mm would stick out each side of your 50mm shell but there would be plenty inside.

Wouldn't want much for it - PM me if it's any good.

bonk man
Posts: 1021
Joined: Sat Mar 20, 2004 22:41 pm

Postby bonk man » Mon Jun 23, 2008 16:55 pm

Cheers people.......... by the time I cobbled together some diy effort I could have earned the money to buy an eccentric.. my engineering skills are pretty poor :)

The Pashley one sounds too small as the closed diameter of my shell is 53 mm tightly shut. I would think the eccentric should be a few mm bigger than the shell to get a tight fit, what do you think?

Steve928
Posts: 314
Joined: Sat Jun 07, 2003 16:35 pm

Postby Steve928 » Mon Jun 23, 2008 17:12 pm

It's this one here, from a Haden shell. Exactly as pictured:

http://www.sjscycles.co.uk/product.asp? ... rc=froogle

So it tuns out to be 53.5mm in diameter. I would think that it needs to be only marginally bigger than the shell, not a couple of mm..?

bonk man
Posts: 1021
Joined: Sat Mar 20, 2004 22:41 pm

Postby bonk man » Mon Jun 23, 2008 20:34 pm

Yeh maybe a tad bigger would do it, I will do a bit of asking around at my local bike shops etc, let me know what you might want for your eccentric, cheers.

Steve928
Posts: 314
Joined: Sat Jun 07, 2003 16:35 pm

Postby Steve928 » Tue Jun 24, 2008 06:01 am

£10 posted

Steve928
Posts: 314
Joined: Sat Jun 07, 2003 16:35 pm

Postby Steve928 » Fri Jun 27, 2008 15:43 pm

PM sent.

bonk man
Posts: 1021
Joined: Sat Mar 20, 2004 22:41 pm

Postby bonk man » Thu Jul 03, 2008 12:10 pm

Steve928 nice one , got the eccentric today and it fits ,,, glory be :D

Now...... :) ........... I have fitted it and moved on to the rear b-b..... der what the hell is going on here then? it is oversize and I don't know whether this is a joke or just an Italian threaded effort, is it normal to have an oversized shell and what do the makers usually fit if it is?

questions questions...... should I ask in know how? or do any special interesters have a swift answer :)

cheers


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