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Tighten Timing Chain

David Nutter2025-08-09 11:16:37
We would like to tighten the timing chain on our tandem, and have this bottom bracket on the front cranks. I don't know the name of it and therefore how to search for instructions, but when we bought it Pete Bird mentioned "tapping some bit of the wedge shaped bit with a hammer". Unfortunately, the bike shop is shut today, so thought we'd reach out to the tandem community for help.
Peter Mynors2025-08-09 11:36:48
There are often a couple of bolts one can slacken underneath the eccentric housing for the front axle.  It is sometimes necessary to remove the bolts entirely and drive in a wedge to further release the grip.  This may be what Pete Bird meant.  See photo attached (this is actually the middle axle on a triplet but the same principle applies).
Robert Lyon2025-08-09 11:43:48
Its an eccentric bottom bracket or ebb. I'm not familiar with that design though so maybe add in wedge. I do think they were known for seizing though so some wd40 might not be a bad start.
Stuart Hibberd2025-08-09 11:54:32

Looks like there are two types with a wedge action to lock the eccentric.

Cannondale 1FG https://www.sjscycles.co.uk/bottom-brackets/eccentric-bottom-bracket-insert-double-wedge-fits-cannondale-rohloff/

Or Bushnell https://problemsolversbike.com/products/bushnell-eccentric-classic-bottom-brackets

Follow the links to see pictures of each type.

Robert Jamison2025-08-09 11:59:19

Hi David,

 

there's probably a you tube video that will help your particular situation if you search something like  'eccentric bottom bracket adjustment'

 

eg.

How to tighten a tandem chain using the eccentric bottom bracket - YouTube

 

Stuart Hibberd2025-08-09 12:00:52
Cannondale 1FG
James Gill2025-08-09 12:04:22

This is the design of Pete's bottom brackets

You need to undo the Allen key bolt and then hit the end of the bolt with a mallet to free up the shims inside. I had to hit ours pretty hard to get it to come loose!

 

https://www.duratec.cz/en/techinfo/technology/eccentric-bottom-bracket/

Stuart Hibberd2025-08-09 12:05:27
Bushnell
Stuart Hibberd2025-08-09 12:07:40
Three types then take your pick!
David Nutter2025-08-09 13:52:43
Thanks all. That's really helpful. It is the duratec one, and once I understood what to do, it was a very straightforward operation. Thanks for the links and advice.