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Synch chain tension

Derek Perry2020-10-21 18:06:14

No then folks,

Fitted a new synch/crossover/front chain on my Dawes Discovery Twin . The chain is the one advertised on JD Tandems website. No matter where I put the eccentric the tension isn't right. I found this on the tinternet 


Is this what I need or am I missing something.



Peter David Koch-Osborne2020-10-21 19:48:48

That link is the same length as a normal link so won't make any difference. You could try a spare chainwheel half way along the front chain to take up the slack. It looks odd, just 'floating' between the upper and lower parts of the chain, but can't come off if the chain is then kept reasonably tight. 

Cheers Peter. 

Ted Savoie2020-10-21 20:17:02


I am afraid you have misunderstood.  By removing a pair of links, one inner and one outer, you remove an inch from the chain.  The half link then only adds half an inch back, so reduces chain length by half inch, and it will solve the problem.  I used them 30 years ago for this very purpose.  It happened in my case when I renovated an old tandem and used an alloy eccentric shell to replace the old steel Brampton eccentric, it had less offset than the original one the frame was designed for.

Ted Savoie2020-10-21 20:24:51
Ted Savoie2020-10-21 20:25:25

I still have three in my spare chain bits box as per pic

Chris Bishop2020-10-21 21:43:21

Do you still have the old chain?
Might be worth checking it to make sure you are on the right track.

Derek Perry2020-10-22 18:05:10

Spoke to JD Tandems and the 3/32" half link is the recommended way to go. So awaiting arrival of said item. I'll keep you posted

Derek Perry2020-10-27 18:31:08

So just a bit of closure on this.Before I started my eccentric bottom bracket was adjusted fully forward and I felt the synch chain was to loose. Took out a link and now too tight with the BB fully to the rear. Put the half link in and now adjustment is spot on with the BB in the middle of it's range of adjustment. Every days a school day as they say.