$Id: index.html 39 2009-10-07 10:22:05Z g $
wippermann connex 808 on Brompton 2 speed
After the 2000 km mark I decided to replace the chain to my black Brompton S2 (54T). The sprockets seem fine:
and these are the old SRAM PC10 and new ConneX chains (102 teeth):
(I seem to have gained 20g from the swap. 266g for the SRAM and 286g for the ConneX. Big deal.)
measurements
The old chain wasn't all that worn, side by side over 102 links against the new one it was under half a link longer, that is under 0.5%. The ConneX is declared as 11/128'' as opposed to the 3/32'' required. This is in contrast to what declared on the Wippermann site→, and I wish on-line shops specified the chain width for all chains! The rollers, measured from the scan above (at higher resolution), are exactly the same. The inner plates' spacing seems to differ more than the nominal 8% (1/128''), but that might just indicate wear in the SRAM chain. I checked the chain over the sprockets and chain-ring before installing it and it looked that there was enough clearance even if slightly narrower. The pins, at about 7.14 mm, are 7 thou (or mils if you like, just to add confusion... that is 0.007'' or 0.1778 mm) longer than PC10 ones.
problem: chain skip
And now the problem: in first gear it all runs smoothly, but in second the chain skips under load once in a while. It seems to be just after the ConneX link (a removable link) leaves the sprocket, as if the link contracted (the first action to remove it) and then re-extended itself. Worrying... I will post images of the link soon. In the meantime I think the solution would be to add a normal link. But... can you reuse a chain pin? [answer: it depends, and as show below, it is not needed.]
solution
As the chain skip happens when the connex link leaves the sprocket (and only the small one), I suspected an interference that would cause the links to fold some way, maybe it was dragged by the ramps on the 16T sprocket. Give that the link is not symmetrical, there are two non equivalent ways of installing it: I must have chosen (so to speak) the wrong one:
This is the lower run of the chain, between chainring and tensioner.
Idling around tonight I had a look on the instructions from Wippermann site→ and indeed they show the other way round (although it looks like a casual choice).
The road test proved the conjecture correct. The connex link must be installed so that the plate on the inside (i.e. the one towards the larger sprocket) has its pin leading with respect to the chain movement (as in the figure above). Provando e riprovando, I retested the wrong orientation of the link, and a few metres in the living room show that it indeed skips.