Yet Another Cycling Forum
General Category => Freewheeling => Tandems => Topic started by: danteetnad on 31 March, 2021, 01:26:05 pm
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Asking the collective: By what method is a 1940s/ 50s gas pipe Tandem Eccentric BB most likely fitted and therefore how to remove it? The fixed and adjustable cups are out. The pinch bolts used to nip up the shell and stop the BB rotating use nuts (not captive threads on the shell - they are free and removed)
Is the eccentric BB threaded into the shell, or is it more likely a press fit and needs persuasion to slide/ forced out? Also got to consider its reinstallation.
Any tips?
Thanks Daniel
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They are notorious for getting stuck.
Sheldon identifies 3 types: https://www.sheldonbrown.com/synchain.html#eccentrics
None are threaded into the shell.
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The eccentric is a slide fit but it is common that corrosion inside the shell or distortion of the pinch bolt ears has locked things up. Photos always help, as does penetrating lubrication.
The first option is to jack the pinch bolts apart. Insert the bolts from the opposite direction (if the pinch bolt ear is threaded) and put disposable washers between the ears. Tighten the bolts until the gap between the ears widens, then tap out the eccentric. Otherwise try to insert a taper (cheap screwdriver?) between unthreaded ears before tapping out the eccentric.
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The fixed and adjustable cups are out.
There's the mistake. Since the eccentric is a sliding fit, if you leave the cups or entire bottom bracket in place you can use a bottom bracket spanner to provide a twist to break any corrosion - remembering of course to undo the pinch bolts first. This has been my technique since I first played with old eccentrics (bottom brackets that is) back in 1970.
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Any tips?
Thanks Daniel
Do it while dressed as the Queen of Sheba?
;D
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Thanks for the replies. Came out without any four letter words being spent on it after working it loose with penetrating fluid and some small wedges between the pinch bolt tabs which allowed some wiggle room.
Next interesting thing is the single side drive- the synch chainwheels are 1/8, but the primary chainwheel
seems to be 3/32- it was working with a 4 speed cyclo freewheel. I was not expecting such a hybrid. Both cranksets are sets are Williams, but the primary crankset is an odd one peice affair, with the 1/8 inner synch chainwheel having a thick 'collar' that fastens it to the crankset to give the required spacing. Neither synch or drive chain wheels are changeable.
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The thought was that having a timing chain that wasn’t designed to derail helped keep it on the chainrings when run a touch too slack. Having a final chain designed to derail helped when changing gears on a multi-speed freewheel, of course.
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Thanks LittleWheelsandBig for the information. I cant run the original 4 sp - the Cyclo block + freewheel is beyond shot, so I think ill put a SA 3 sp with a 3/32 cog + hub brake in there. ebay here i come...
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Spreading the dropouts and/or fitting a 5/6sp freewheel not an option? IanH OTP probably has some knowledge about revamping old tandems.
SA did a tandem-specific 3sp hub but quite a few were equipped with standard AWs. Rogerzilla knows more about that sort of thing than me but I think they lasted ok-ish if you didn’t muscle it too much.
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Could be, but it's a KISS project for flat land pootling, the drop-outs are 126 so there will be something knocking about that is close enough, with a hub brake hopefully, & honestly, I'm not a fan of Derailluers anymore. The only thing I've got with more than three gears is the trike, and the gears on that present more than enough hassle for me!
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It will be fine for pootling around.
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A guy in Swindon CTC ground the planets to bits on a standard AW but I don't know what his lowest gear was, or whether he did it with an all-male racing crew. He was pretty fast on a solo. You could possibly reduce the risk by quartering the cranks, but not everyone likes that.