Mercury with saggy chain - take out a link or adjust eccentric

[alcyst]

I don't know enough bike mechanics to have an opinion on this so any advice is appreciated.
I have a Mercury, the chain is indicating as not worn, but is loose enough to get thrown off on rough surfaces. How do I go about fixing this? Looks like removing a link or adjusting eccentric is the solution, though a new chain may be appropriate? Is there a single right answer or can any approach be correct?

Thanks

[JimK]

Adjusting the EBB can certainly fix a chain that is so loose that it falls off. Generally you can tighten the EBB a few times before removing a link. When the EBB is at the outer limit, removing a link ought to bring it back near the inner limit. I haven't gotten to that point yet! If the EBB is not near the outer limit, I expect that removing a link will shorten the chain so much that even at the inner limit the chain will be too short/tight.

One fun debate is how frequently to switch chains. A worn chain will push the wear on the sprocket and chainring - that's the theory, anyway. I started out going through a few new chains, switching before the EBB got to the outer limit. But then it seemed that the sprocket and chainring were worn enough that a new chain wasn't fitting so well. At this point I have run out of theories!

[Danneaux]

Hi Alcyst!

In terms of chain slack takeup and service life, the Mercury is aimed at a different audience than Thorn's expedition touring bikes. It is equipped with a different eccentric bottom bracket that offers less adjustment, and indeed chain replacement is required for the Mercury where one could simply get by with an adjustment on, say, a Nomad.

Here are Andy Blance's words on the matter, drawn from page 16 of the Mercury brochure Issue 27, Summer 2013 ( http://www.sjscycles.com/thornpdf/ThornMercuryHiRes.pdf ):

I’ve designed a new mini eccentric for the Thorn Mercury. I wish to state clearly that there’s no intention of offering this on any of the other models.

In order to actually save weight, the eccentric had to be smaller in diameter.  

Being smaller in diameter means that it can only adjust a little more than half a link of chain. When no more adjustment can be made with the eccentric, a new chain must be fitted. By choosing one of the ideal chain ring and sprocket  combinations, the service life of the chain is maximised.
 
I believe that customers, who require a sports bike, will be prepared to replace the chain. Such cyclists will certainly find obtaining and fitting a replacement chain and servicing the mini eccentric, easier than the expedition cyclist. Servicing and preparing
the bike for an important event ought to be normal practice.

So, chain replacement is required followed by a special cross-bolt tightening procedure unique to the Mercury's EBB, also detailed on page 16 at the link above.

Best,

Dan.

[alcyst]

Thank you gentlemen.

Guess the chain checker is superfluous. The spare chain I'd bought is going on tonight.

[macspud]

If you have already used up all the adjustment on the eccentric? It does sound like it's time for that new chain right enough.

[alcyst]

Looking at the KMC chains I noticed the Missing Link Connector & Removal tools, are they worth buying?

[Danneaux]

Hi Acyst!

I've been really pleased with the service life of my KMC chains and their Missing Link connectors especially. I probably go counter to form and disconnect my chain when removing the Nomad's rear wheel for repair or transport. It makes wheel removal easier for me and the bike is much easier and cleaner to transport in a car with wheels off if the chain is residing in a zip-top plastic bag (yes, I carry spare connectors in my underseat bag against the possibility of loss).

If you decide to do the same, be aware there likely won't be sufficient slack in a well-adjusted chain to remove the link on a Rohloff drivetrain. To remove the connector, I just drop the rear wheel until it just clears the dropout and that frees up enough slack to disconnect the link. Exactly one year ago, I made a picture-tutorial showing how these connectors work; you can see it here: http://www.thorncycles.co.uk/forums/index.php?topic=4461.msg23025#msg23025

Best,

Dan.

[Andre Jute]

Looking at the KMC chains I noticed the Missing Link Connector & Removal tools, are they worth buying?

KMC chains come with one missing link connector fitted. It is worth having a spare set or two. I've found the tool useful for getting the missing links on and off.

The supposed "toollessness"  of missing links (anybody's) is marketing guff. It is definitely worth having a tool to deal with missing links, but KMC makes you buy two, one for removal, one for assembly. Instead I bought one tool that does both jobs. Either of these will do.

http://www.chainreactioncycles.com/ie/en/park-tool-master-link-pliers-mlp1-2/rp-prod109888
http://www.chainreactioncycles.com/ie/en/bbb-open-link-closing-link-tool-btl77/rp-prod47439

I don't carry it on the bike. It stays in the pilot's flight case I now use for a bicycle toolbox. It saves frustation and bleeding fingers and broken nails when grit gets into these links, which in my experience is always.