Thorn Cycles Forum
Community => Thorn General => Topic started by: alcyst on August 06, 2014, 07:34:53 PM
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The chain jumped on my Mercury so I went to adjust the eccentric. Getting the screws off was no problem and they still showed some signs of copper slip. Problem arose then, the eccentric didn't seem to want to budge. The question is should it slide fairly freely, or should it need "encouragement"? I do have the supplied tool.
The photos in the brochure show the eccentric with cranks removed, is that recommended?
I re-slipped the screws and re-installed in the right order to the correct torque. That part of the job is actually easy enough.
In the end I just put on a new chain, so that if I cannot take pride in my bike maintenance I can at least look at the pristine chain. The Park Tools MLP 1.2 is worthwhile.
The Mercury does actually have 3 bottle cage bosses, I had completely missed that until looking through the brochure for this job.
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I adjusted mine this week, having backed all the bolts off all the way. it was initially stiff to move, but a little leverage on the crank arms helped. The tool seems prone to jumping out, so it becomes a three handed job to hold the tool in place, and turn it, and steady the bike. There's a suggestion somewhere on the thorn site that, if it's stiff, place a coin in the gap and tighten a bolt against that, as it will push the jaws open gently.
All this looks like it is manageable with the crank in place.
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whats the idea behind these eccentric bb ,is the purpose just to adjust the chain tension?
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https://www.youtube.com/watch?v=QtHBwbEIgps might help
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https://www.youtube.com/watch?v=QtHBwbEIgps might help
Dave, & Hubs, thanks for that. That frame looks a touch cleaner than mine.
Edit, I use a € 1 cent coin to open my bracket enough to allow the eccentric to move.
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yes, the vertical dropout which holds the Rohloff mini torque arm means that it needs either an eccentric BB or a chain tensioner to adjust tension.
whats the idea behind these eccentric bb ,is the purpose just to adjust the chain tension?
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Thanks hubs that answer was a long time coming ;)
i'm not a fan of rohloff hubs and that bb set up is dire .i cant imagine campagnolo would come up with a design like that to take up the slack of a chair ::)
jags.
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I agree that adjusting the chain on eccentric bottom brackets look crude but it is effective. It would be nice if it could be a thing of beauty but hey ho. Personally I think most derailleur set ups look pretty ugly (Campag apart) and a lot more time consuming to set up right. Both systems have their pro and cons.
Neil.
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Eccentric BB with no chain tensioner needed makes for a nice, clean, straight chain-line and much less drag in your drive-train IMHO.
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Throwing the proverbial spanner into the works: Gates Carbon belt drive anyone?
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but why would you need to adjust it why does the chain come slack in the first place. ::)
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I'm sure someone with more technical knowledge will explain better than me but a new chain seems to require the slack taking up very quickly (maybe 100-200 miles) but then will rarely need adjusting for the duration of it's life. On average a chain lasting say 6,000 miles would need adjusting around 3 or 4 times in my experience.
It only takes 2 minutes to take the slack up and tighten the bolts so the maintenance is minimal.
Neil.
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that il do ;) thanks
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I agree that adjusting the chain on eccentric bottom brackets look crude but it is effective. It would be nice if it could be a thing of beauty but hey ho.
The BEST EBB in my opinion - Bushnell. A real crying shame (literally) that it is about 1-2mm too big for a Thorn shell :'(
(http://www.daveyatescycles.co.uk/uploads/images/Custom%20frames/Ebb.jpg)
(http://construct.typepad.com/.a/6a00d8354dc5ac69e201053696a8cc970b-pi)
No pinch-bolts, just one easy-to-use hex-bolt. Anyone need one, I have a nice new one for sale.
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So the hex bolt tightens things up rather than 2 bolts with points on digging into the soft metal of the EBB?
Sounds a good method if true.
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Although not as neat as the approach above, the Mercury uses a clamping mechanism rather than the two bolts into the EBB of the other Thorns.
On chain wear, I suspect that even Campag chains wear and snap on occasion!