Technical > Transmission

How often to adjust the eccentric BB

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RobertL:
Coming up on 24,000 miles on my RST. Around the 21,000 mile mark the chain was getting loose and dropping off on bumps, the bike shop adjusted the eccentric BB with the Thorn tool and using torque wrench. 3,000 miles later getting the same problem.

Is this an eccentric BB age thing? I change the chain every year, and the chainring/sprocket every third year, so coming up this summer.

Fortunately 97% of the journeys are commuting, but am glad this problem is not surfacing on a long distance expedition miles from civilization.

PH:
When it needs it, there's too many factors to put a time or distance on that.
It's a 5 minute simple job, about the same level of complexity as fixing a puncture, do you really need a bike shop to do it for you?

RobertL:
In theory no, but there is a torque required when adjusting or you risk it either slipping again, or damaging the BB? Am guessing you can adjust with screwdrivers, but ideally you would be carrying the dedicated adjustment thingymagig.

UKTony:
As a start I suggest you look at pages 12-14 of this

http://www.sjscycles.com/thornpdf/ThornBikeOwnerManual2Web.pdf

It sounds like you’re waiting far too long to re-tension the chain. It’s quite a simple DIY job.

If the chain slackens very soon after an adjustment it could be that the EBB is slipping because the LBS hasn’t used a high enough torque when tightening the EBB securing screws and/or that the EBB shell screws pointy ends are slipping into the dints in the alu shell made by earlier adjustments. If the dints in the shell from previous adjustments are coalescing then It might be time to replace the EBB shell.

PH:

--- Quote from: RobertL on June 17, 2022, 10:19:50 am ---In theory no, but there is a torque required when adjusting or you risk it either slipping again, or damaging the BB? Am guessing you can adjust with screwdrivers, but ideally you would be carrying the dedicated adjustment thingymagig.

--- End quote ---
In the manual Tony linked the recommended torque is 10 - 17 Nm, that's a huge range and I'd expect that to have a reasonable margin for error.
I don't remember knowing there was a recommendation when I had my set screw EBB, I certainly never used it.  With a standard length spanner, 10-17 Nm is fairly tight without hanging off the spanner like a gorilla.  Maybe try it at home a couple of times with a torque wrench to get an idea of what it feels like. I wouldn't go by feel if it was a precise measure, but aim for 15 and you ought to be able to get within 20% +/-.
Re needing adjustment after 3,000 miles.  That doesn't seem unusual to me, I log such things and get anything between 500 and 4,000, but usually somewhere in the middle of that.  Different makes and models of chain also behave differently, all the KMC chains I've used have needed adjustment after a few hundred miles, I've assumed this was some sort of settling process rather than wear, as they then don't need it again for a long while. I don't get that with SRAM chains and it's a long while since I used Shimano. 

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