Tandem eccentric bottom bracket conundrum

bonk man

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

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

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

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

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

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

£10 posted

Steve928

PM sent.

bonk man

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

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